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3 1293 013994

“35‘s —LIBRARY
*1 Michigan State
University

 

 

 

This is to certify that the

thesis entitled

Supercritical Fluid Extraction of Polycyclic
Aromatic Hydrocarbons from Soil Matrices

presented by

Mark S. Ruppel

has been accepted towards fulfillment
of the requirements for

M.S. Environmental Engineering

degree in

 

 

WWW/fl 27442234.,

jor professor

Date Jag. 7,, #75”

0-7639 MS U is an Affirmative Action/Equal Opportunity Institution

 

 

PLACE Ii RETURN BOX to romavothb checkout from your record.
TO AVOID FINES return on or baton dot. duo.

DATE DUE DATE DUE DATE DUE

       

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

MSU is An Affirmative Actionféqucl Opportunity imtitmion
Wm:

.-.. __—.

SUPERCRITICAL FLUID EXTRACTION OF POLYCYCLIC AROMATIC
HYDROCARBONS FROM SOIL MATRICES

By

Mark S. Ruppel

A TI—IESIS

Submitted to
Michigan State University
in partial fiJlfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Civil & Environmental Engineering

1995

ABSTRACT

SUPERCRITICAL FLUID EXTRACTION OF POLYCYCLIC AROMATIC
HYDROCARBONS FROM SOIL MATRICES

By

Mark S. Ruppel

The primary objective of this thesis is to analyze the effectiveness of supercritical
fluid extraction (SFE) for the determination of polycyclic aromatic hydrocarbons (PAHs)
in soil. Ottawa Sand is used as an inert material to extract PAHs from using C02
modified with 1% methylene chloride. Soil A is a clean, horizon A soil that is used to test
the extractability of spiked PAHs. Soil C was obtained from an actual coal tar
contaminated site and is used to test the extractability of native PAHs. It was found that
the solubility of PAHs in the supercritical fluid was not a limiting factor. The extraction of
the native PAHs in Soil C was most likely due to diffusion limitations. Addition of an

organic modifier had a large effect on the recovery of native PAHs from Soil C.

Dedicated to:

my high school chemistry teacher, Mr. Schultz

iii

ACKNOWLEDGMENTS

First and foremost, I would like to acknowledge Leslie M. Neilson for her support and
friendship. I want to thank Dr. Susan Masten for giving me guidance and direction during my
research. I also want to thank all of the Faculty and Staff of the Civil and Environmental
Engineering Department for providing me with an excellent learning environment. I would
like to thank Michigan Biotechnology Institute (MBI) for the opportunity to work in the
environmental engineering field and providing me with a means to support myself. Finally,
special thanks to all of the MBI employees that gave me assistance throughout my research,

especially the 8165.

iv

TABLE OF CONTENTS

LIST OF TABLES:
LIST OF FIGURES:

CHAPTER 1: Introduction
1.1 Objective
1.2 Organization of Thesis

CHAPTER 2: Background
2.1 Temperature and Pressure
2.2 Matrix Efi‘ects
2.3 Supercritical Fluids and Modifiers
2.4 Analyte Collection

CHAPTER 3: Methodology
3.1 SFE Apparatus
3.2 Quantitative and Qualitative Analysis
3 .3 Reagents
3 .4 Soil Characteristics
3 .5 Spiking Procedure
3 .6 SFE Procedure
3.7 Soxhlet Extraction Procedure

CHAPTER 4: PAHs Extracted From Ottawa Sand
4.1 Temperature and Pressure Effects

CHAPTER 5: PAI-Is Extracted From Soil A
5.1 Extractions of Fresh Spike using 90 °C and 300 atm
5.2 Extractions of Fresh Spike using 150 °C and 300 atm
5.3 Extractions of Fresh Spike using an Organic Modifier
5.4 Extractions of Aged Spike using 90 °C and 300 atm
5.5 Extractions of Aged Spike using an Organic Modifier
5.6 Extractions of Aged Spike using an Organic Modifier and 150 °C

vii

39
39
39
42
43
52
54

CHAPTER 6: PAHs Extracted From Soil C

6.]
6.2
6.3
6.4
6.5
6.6
6.7
6.8
6.9

Soxhlet Extraction

Fractionated Extraction with SFE at 90 °C and 300 atm

45 Minute Dynamic Extraction with SFE at 90 °C and 300 atm
Fractionated Extraction using an Organic Modifier

45 Minute Dynamic Extraction using an Organic Modifier
Fresh Spike Recovery using an Organic Modifier

Solvent Rinse of Cryogenic Trap

Aged Spike Recovery using an Organic Modifier

Fractionated Extraction using an Organic Modifier and 150 °C

6.10 CD; and Modifier Contact Time

CHAPTER 7: Conclusions and Recommendations

7.1
7.2

Conclusions
Recommendations

APPENDICES
Appendix A: Physical Characteristics and Structures of PAHs
Appendix B: Soxhlet Extraction Procedure for

PAH Contaminated Soil

Appendix C: Cost Comparison of SFE and Soxhlet

Extraction Methods

REFERENCES:
List of References

vi

56
57
57
62
65
65
71
73
75
78
81

86

86
87

9O

93

95

98

Table 2.1

Table 2.2

Table 2.3

Table 2.4

Table 3.1

Table 3.2

Table 3.3

Table 4.1

Table 4.2

Table 4.3

Table 5.1

Table 5.2

LIST OF TABLES

Physical Properties of Commonly Used Supercritical Fluids
Hydrocarbon Recovery from Soil SRS 103-100

Experimental Conditions for the Low and High Recoveries
of 12 PAHs

Supercritical Fluid Extraction Efficiencies Using Different
Modifiers and Modifier Concentrations

Mechanical Characteristics of Soils used in Experiments

Concentration of PAHs Added to Soil A and Soil C for
the Aged PAH Spike

SFE Conditions used for the Extraction of PAHs from
the Soil Matrices

Percent Recovery with Varying Pressure at a Constant
Temperature of 120 °C

Percent Recovery with Varying Pressure at a Constant
Temperature of 150 °C

Percent Recovery with Varying Temperature at a Constant
Pressure of 300 atm

SFE Conditions used for the Extraction of Fresh Spike
PAHs from Soil A

Percent Recovery of PAHs from Soil A with the SFE
at 90 °C and 300 atm

vii

I9

28

30

31

36

36

37

40

42

Table 5.3

Table 5.4

Table 5.5

Table 5.6

Table 5.7

Table 5.8

Table 5.9

Table 5.10

Table 6.1

Table 6.2

Table 6.3

Table 6.4

Table 6.5

Percent Recovery of PAHs from Soil A with the SFE
at 150 °C and 300 atm

Percent Recovery of PAHs from Soil A with the SFE
at 90 °C and 300 atm with 500 pl of Methylene Chloride
Added as an Organic Modifier

Percent Recovery of PAHs from Aged Spike Soil A
with SFE at 90 °C and 300 atm

Concentration of PAHs Determined by Soxhlet Extraction
in Aged PAH Spiked Soil A

Percent Recovery of PAHs by Soxhlet Extraction Based
on Theoretical Concentrations in Aged PAH Spiked Soil A

Percent Recovery of PAHs from Aged Spike Soil A with
the SFE at 90 °C and 300 atm Relative to the Soxhlet
Extraction Recoveries

Percent Recovery of PAHs from Aged Spike Soil A with
the Addition of 700 pl Methylene Chloride as an Organic
Modifier SFE at 90 °C and 300 atm Relative to the
Soxhlet Extraction Recoveries

Percent Recovery of PAHs from Aged Spike Soil A with
the Addition of 700 pl Methylene Chloride as an Organic
Modifier SFE at 150 °C and 300 atm Relative to the

Soxhlet Extraction Recoveries

Concentration of Native PAHs in Soil C Determined by
Soxhlet Extraction

SFE Conditions used for the Extraction of Native PAHs
from Soil C

Percent Recovery of PAHs from Soil C with the SFE
at 90 °C and 300 atm

Percent Recovery of PAHs from Soil C with the SFE
at 90 °C and 300 atm

Percent Recovery of PAHs from Soil C using an
Organic Modifier

viii

43

44

47

49

50

50

52

54

58

59

60

63

66

Table 6.6

Table 6.7

Table 6.8

Table 6.9

Table 6.10

Table 6.11

Table A

Table B

Table C

Percent Recovery of PAHs from Soil C using an
Organic Modifier

Percent Recovery of Fresh Spiked PAHs from Soil C
using an Organic Modifier

Difference in Native PAH and Spiked plus Native PAH
Concentrations

Percent Recovery of PAT-Is from Soil C using an Organic
Modifier and Different Cryogenic Trap Rinse Solvents

Difference in Native PAH and Spiked plus Native PAH
Concentrations as Determined by SFE and Soxhlet Extraction

Percent Recovery of PAHs from Soil C using an Organic
Modifier and Temperature of 150 °C

Physical Characteristics and Structures of PAHs

Soxhlet Extraction Consumables Cost

SFE Consumables Cost

ix

68

72

72

74

77

79

90

96

97

Figure 5.1

Figure 5.2

Figure 5.3

Figure 5.4

Figure 5.5

Figure 5.6

Figure 5.7

Figure 6.1

Figure 6.2

Figure 6.3

LIST OF FIGURES

Fractionated Collection During SFE of Fresh PAH
Spike from Soil A with SFE at 90 °C and 300 atm

Fractionated Collection During SFE of Fresh PAH
Spike from Soil A with SFE at 150 °C and 300 atm

Fractionated Collection During SFE of Fresh PAH
Spike from Soil A with 500 pl Methylene Chloride
Modifier and SFE at 90 °C and 300 atm

Fractionated Collection During SFE of Aged PAH
Spike from Soil A with SFE at 90 °C and 300 atm

Fractionated Collection During SFE of Aged PAH
Spike from Soil A with SFE at 90 °C and 300 atm
Relative to Soxhlet Extraction Results

Fractionated Collection During SFE of Aged PAH
Spike from Soil A with 700 pl Methylene Chloride
Modifier and SFE at 90 °C and 300 atm

Fractionated Collection During SFE of Aged PAH
Spike from Soil A with 700 pl Methylene Chloride
Modifier and SFE at 150 °C and 300 atm

Fractionated Collection During SFE of Native PAHs
from Soil C with SFE at 90 °C and 300 atm

PAH Concentrations Determined by Fractionated
Collection and 45 Minute Dynamic

Fractionated Collection During SFE of Native PAHs
from Soil C with 700 pl Methylene Chloride Modifier
and SFE at 90 °C and 300 atm

41

45

46

48

51

53

55

61

64

67

Figure 6.4

Figure 6.5

Figure 6.6

Figure 6.7

Figure 6.8

Figure 6.9

Figure 6.10

PAH Concentrations Determined by Fractionated
Collection and 45 Minute Dynamic with 700 pl
Methylene Chloride Modifier

Concentration of PAHs Recovered from Soil C with
and without Methylene Chloride Modifier

Aged PAH Spike Recovery fiom Soil C by SFE and
Soxhlet Extraction Methods

Percent Recovery of Native PAHs from Soil C using
Organic Modifier with SFE at 150 °C and 300 atm

Concentration of PAHs Recovered from Soil C with
Change in Static Extraction Time

Concentration of PAHs Recovered from Soil C with
Change in Static and Dynamic Extraction Time

Concentration of PAHs Recovered from Soil C after
Different Extraction Times

xi

69

70

76

80

83

84

85

CHAPTER 1

INTRODUCTION

The environmental industry relies on dependable quantitative analytical methods to
allow for the successfiil protection and remediation of the environment. When
determining contaminant levels, some of the most difficult matrices with which to work
are soil, sediment, and other solid material. Conventional methods, such as sonication and
soxhlet extraction techniques, are commonly used for the analysis of solid material, and
have been approved by the United States Environmental Protection Agency (US EPA) for
this use. Another method that has been gaining attention is supercritical fluid extraction
(SFE). SFE is an analytical tool that can potentially save time, reduce hazardous waste,
and be less expensive than conventional extraction techniques. There is a need for more
research concerning SFE to determine the potential and limitations of this technique for

applications in the environmental industry.

1.1 Objective

The primary objective of this thesis is to analyze the effectiveness of SF E for the
determination of polycyclic aromatic hydrocarbons (PAHs) in soil. PAHs can be spiked
onto soil to develop extraction methods for the quantitation of contaminants, but they may

not have the same matrix interaction characteristics as native PAHs. The term native

refers to the contaminants present in the soil as a result of environmental pollution. In the

case of coal tar contamination, the native PAHs have had time to interact with the soil

matrix and are likely to be more difficult to extract quantitatively than fresh spike PAHs.

Extraction of spiked PAHs will usually result in an overestimation of the extraction

method efficiency. The research results should indicate whether or not the SF E

information gained from spiked PAH extractions can be used as a template for SFE

method development for native PAHs. The above objective was obtained by the

following:

o Extracting PAHs from soil using different SFE temperatures and pressures

o Extracting PAHs from various types of soil

0 Investigating the aging process and its effect on extraction efficiency

0 Conducting experiments which may indicate whether solubility or diffusivity are
limiting physical parameters

0 Comparing the efficiency of SFE vs. conventional methods for the analysis of native

PAHs is soil

1.2 Organization of Thesis

The first part of this thesis describes the general background and technical
information. Chapter 2 provides information on various applications of supercritical fluids
and research that has been done to investigate the parameters that influence SF E

efficiency.

The second part of the thesis describes the experiments performed and summarizes
the experimental findings. The experimental methods and equipment used for this
research are described in Chapter 3. The extraction of PAHs from Ottawa Sand using
SFE is described in Chapter 4. Chapter 5 contains information about the SFE of PAHs
that were spiked onto a clean soil. The SFE of native PAHs from a coal tar contaminated
soil is described in Chapter 6. Chapter 7 summarizes the experimental findings and

presents recommendations for further work.

CHAPTER 2

BACKGROUND

The applications of supercritical fluid technology have been expanding rapidly into
many new areas. There have been new and continuing developments in the application of
SFE for pharmaceuticals, polymers, chromatography, extractions, coal and petroleum
processing, and environmental remediation (Kiran, 1993). In the environmental area, the
. applications for supercritical fluids range from the actual clean-up of contaminated soils to
the laboratory analysis of contaminants (1-45). Supercritical fluid chromatography (SFC)
and supercritical fluid extraction (SF B) have been used both independently and together as
tools for analytical analyses. SFE is a technique that can save both time and money while
reducing the amount of waste generated in the analytical laboratory.

A supercritical fluid is a pure substance that is above its critical temperature and
pressure. When a substance is above its critical point it exhibits physical properties of
both a liquid and a gas. In choosing the appropriate solvent for an extraction process two
important points have to be considered (Engelhardt, 1991):

o Selectivity: In order to avoid additional separation processes, the solvent should
extract only the components of interest.
0 Suitability: The extractor should be removable without loss of the components of

interest. In other words, there should be large differences in the volatility of the

5

extract and the extractor. Also, there should be no thermal strain, excessive heating,

applied to the extracted solvents.
Both of the above criteria can be met by application of supercritical fluids. A table of
physical properties of commonly used substances for the extraction of analytes from
various matrices are shown in Table 2.1. One of the most common supercritical fluids
used for analytical applications is carbon dioxide (C02). The critical temperature and
pressure for C02 are 31 °C and 73 atm. Supercritical fluid extraction (SFE) takes
advantage of the solvating power of substances that are in a supercritical state. The
properties of viscosity and solute diffusivity are more typical of gases than liquids and
contribute to improved mass transfer for solutes in the supercritical state, and therefore,
increase extraction rates (Snyder, 1992).

SFE can be used as an effective analytical tool for the analysis of environmental
contaminants in soil matrices, but care must be taken in developing the SFE method. The
difficult part of applying SFE as an analytical tool is determining how the variables will
effect the extraction performance. The control parameters must be modified to
accommodate the analyte of interest and the matrix. Temperature and pressure are two
important parameters that need to be optimized in order for SFE to be effective.
Changing the temperature and pressure will change the density of the supercritical fluid,
which affects the solvating power of the fluid, thereby affecting the performance of SFE
(Langenfeld et al., 1993). There has been a great deal of research done to investigate the
parameters that effect the performance of SFE. Research investigations on other

parameters such as the matrix, extraction modifiers, and analyte collection have also been

6

conducted (1-45). The rest of this chapter contains information about research done on

these parameters. The research done for this thesis addresses these parameters and how

they affect the SFE of PAHs from soil.

. .. (0

Table 2.1

Physical Properties of Commonly Used Supercritical Fluids

 
    

» (debyes);

 

?' :..:::.:: “7112231:

Dipole ' ' ’ " ‘ ' ' -

   

 

31

 

0

Fat, PCBs, pesticides,
PAHs, vitamins,
polymer additives,
hydrocarbons,
halocarbons, aromatics

Meats, soil, Tenax,
PUF, polymers,
air particulates,
sedimentatry rock

 

COz/MeOH

41*

74*

Pesticides, priority
pollutants
(semivolatiles)

Soils, plant tissue,
sludge

 

N20

37

72

0.2

Amines, dioxin,
dibenzofurans

Soils, fly ash

 

CHCle

96

49

1.4

PCBs, PAHs

Sludge, soils

 

 

CzHo

Tc - Critical Temperature
Table of information taken from Snyder. 1992

32

 

 

48

 

0

Pc - Critical Pressure

2.1 Temperature and Pressure

 

PAHs

 

Sediment, fly ash,
air particulates

* - Modified with 5% (v/v) methanol

Changes in temperature and pressure during SFE will result in variations in the

density of the supercritical fluid, thereby affecting the solvation power of the supercritical

fluid. The solubility of a solute in a supercritical fluid will increase with increasing density

(Snyder, 1992). An increase in pressure will increase the density of a supercritical fluid

and it is possible to achieve densities that are higher than those of some liquids (Snyder,

 

7

1992). Temperature has the opposite effect on density; increasing the temperature will
decrease the density, therefore decreasing the solvation power. However, higher
temperatures may be appropriate for analytes with low vapor pressures (Snyder, 1992).
There has been a significant amount of research done on how temperature and pressure
affect the extraction of analytes during SFE. Various results have been reported on a
variety of compounds and matrices.

Lopez-Avila et al. (1992) used a standard reference soil, (SRSlO3-100) purchased
from Fisher Scientific, for experiments to determine the effect of temperature and pressure
on the recovery of TPH. The SFE conditions tested included three pressures, 150, 250,
and 350 atm, and two temperatures, 55°C and 90°C; results are shown in Table 2.2. The
recovery of total petroleum hydrocarbons (TPH) from the PAH contaminated soil
increased with an increase in pressure. However, the recovery appears to be inversely

dependent on temperature (Lopez-Avila et al., 1992).

Table 2.2

Hydrocarbon Recovery from Soil SRS103-100

 

 

 

 

 

 

55 °C 77% 96% 98%
90 °C --- 85% 82%

* 150 atm and 55 °C - extraction time 120 minutes
* All other conditions - extraction time 60 minutes

 

8

The higher pressure resulted in a shorter extraction time required to obtain quantitative
results, however the increase in temperature actually lowered the extraction efficiency of
the TPHs from the test soil.

Ho and Tang (1992) conducted SFE experiments using a 23 factorial design to test
the effect of three factors at two levels. The three factors tested were temperature,
pressure, and extraction time. The two levels tested for each factor were temperatures of
40 °C and 80 °C, pressures of 100 atm and 300 atm, and extraction times of 10 minutes
and 40 minutes. There was also a middle value tested: 60 °C, 200 atm, and 20 minute
extraction time. A total of 29 compounds, including PAHs and organochlorine pesticides,
was extracted from a commercially available liquid-solid extraction cartridge. The
extraction cartridge contained 500 mg of silica gel with chemically bonded C18 octadecyl
groups. Pressure was found to be the most influential variable that affected the recoveries
of all the compounds. An increase in the pressure resulted in an increase in recovery of
the analytes. At moderate pressure conditions from 350 to 400 atm and extraction time
from 20 to 35 minutes, most of the analytes were quantitatively recovered from the C18
cartridge (Ho et al., 1992). Temperature affected the recoveries of only a few
compounds. It had a positive effect on compounds such as chrysene, benzo[a]anthracene,
and phenanthrene. Table 2.3 contains a list of 12 PAHs and the specific variables that had

a statistically significant effect on the recovery of each individual PAH.

Table 2.3

Experimental Conditions for the Low and High Recoveries of 12 PAHs

Compound _ -.

 

, _ . 01m:

:52 9".‘Lowand mgr i? g. 3.:9 i 3.: 432:; .' ~ - ' ~
Mean Recovery" . .fi' _
. (ti/Q) I £1512.“ {iii'E-ffi'iifi£5513"it :3": .. -. .. .. .. 423352- 5. 3'f.'-i;.i¥-'

. T:
1;
’-. .3-

 

.. Naphthalene i i

25

19.97
83.5, 84.7

low

high

 

HLI-LMMM

 

Acenaphthylene

25

0.26
94.56

low
high

LHL
HLH

 

Acenaphthene

25

0.3, 0.5
101

low

high

LLL, LHL
MMM

 

Fluorene

25

0.10, 0.18
100

low
high

LLL, LHL
IHL,FHH.,IH,FLFHH1,RWM

 

Phenanthrene

25

low

high

0.24, 0.25
93.8

LLL, LHL, LHH
MIVIM

 

Anthracene

25

0.0
93.7

low
high

LLL, LHL, LHH
MMM

 

F luoranthene

25

0.0
85.0

low
high

LLL, LHL, LHH
HHL, HHH, MMM

 

Pyrene

25

0.0
89.04

low
high

LLL, LHL, LHH
HHH

 

Chrysene

25

low
high

0.03, 0.25
74.99

LLL. LHL, LHH
HHH

 

Benzo[a]anthracene

50

0.0
70.03

low
high

LLL, LLH, LHH
HHH

 

Benzo[b]fluoranthene

25

0.0
87.4

low
high

LLL, LHL, LHH
HHH

 

 

Benzo[a]pyrene

50

 

 

0.0
31.0

low
high

 

LLL,LLH,LI-IL,LHI-I,I-HL,HI~IL

 

HHH

*For PT eT. (LHL) represents low level for pressure; high level for temperature; and low level for
extraction time. and (MMM) represents middle level for all factors.
“Table of data from Ho and Tang (1992)

10

Extractions were performed by Langenfeld et al. (1993), on three different
materials to recover PCBs from river sediment and PAHs from soil and air particulates.
The extractions were carried out using two different temperatures, 50 °C and 200 °C. At
50 °C, pressures of 350 atm and 650 atm were tested, and at 200 °C, pressures of 150
atm, 350 atm, and 650 atm were tested. At 50 °C, raising the pressure from 350 atm to
650 atm had no effect on the recovery efficiency for any of the samples. The river
sediment (NIST SRM 1939) was contaminated with PCBs and efficient extractions were
obtained only when the temperature was raised to 200 °C. Quantitative extractions were
obtained in 40 rrrinutes, regardless of the temperature, for a soil highly contaminated with
PAHs (“US EPA Certified” PAH Contaminated Soil, Lot No. AQ103, Fisher Scientific).
In contrast, a PAH contaminated air particulate sample (NIST SRM 1649) showed an
increase in recovery when both higher temperatures and pressures were used. Their
results indicate that temperature is more important for achieving high extraction
efficiencies than pressure when the pollutant molecule interaction with the sample matrix
is strong. In contrast to the urban air particulates, PAHs from the highly contaminated
soil were quantitatively extracted using mild temperatures (50 °C), indicating that these
PAHs are not strongly bound to this sample matrix and very little energy is required to
desorb them from the sample matrix (Langenfeld, 1993). There was a large difference in
the concentration of PAHs in the air particulate sample and the soil sample. The PAHs on
the soil were 33 to 200 times more concentrated than those on the air particulates. When
there is a low concentration of PAHs, the percentage of PAHs bound to strong reactive

sites will be high. This is because the reactive sites outnumber the PAHs available. A

11

lower percentage of PAHs will be bound to strongly reactive sites when a high
concentration of PAHs is present. In this case the PAHs outnumber the available reactive
sites. Also, the processes by which the two samples were contaminated are different. The
PAHs were spilled onto the soil, while the air particulates and PAHs are likely to be
formed together with soot during the combustion of vehicular firels (Langenfeld et al.,
1993)

Levy et al. (1993), came to a similar conclusion about analyte association with the
matrix and the variables that affect efficient recovery using SFE. They state that, “SFE
strategies are dependent on the solubility or kinetic limitations, which relates to the level
of association of the target analytes with the respective heterogeneous sample matrices”.
SFE was performed on a soil contaminated with PAHs. The temperature held constant at
75 °C during SFE. Three different pressures (250 atm, 350 atm, and 450 atm) were
investigated to determine their affect on analyte recovery. All three pressures gave
acceptable results for the lower molecular weight PAHs, but the highest pressure resulted
in the best efficiency for extracting all of the PAHs.

Levy et a1. (1993) investigated the affect of temperature on extraction efficiencies.
Marine sediment and a river sediment contaminated with PAHs were used for this
experiment. Pressure was held constant at 475 atm while the temperature used for the
extractions was varied. The marine sediment was extracted at 65 °C, 80 °C, and 150 °C.
The river sediment was extracted at 40 °C, 100 °C, and 150 °C. The best recoveries were

obtained using the highest temperature of 150 °C for both the marine and river sediments.

12

It was determined from the results that raising the extraction temperature and pressure will
increase efficiencies for the extraction of PAHs from soils and sediments.

Hawthorne and Miller (1986) investigated the extraction efficiency for PAHs on
Tenax-GC traps. They were able to quantitatively recover PAHs from Tenax-GC traps
using CO; with a 15 minute extraction time, a temperature of 45 °C, and a pressure of 200
atm. Myer et al. (1992) investigated the effect of temperature on the extraction efficiency
of PAHs from soil. The pressure was held constant at 350 atm and the total extraction
time was 120 minutes. The extract was collected in three fractions; the first after 30
minutes at 90 °C, the second after another 30 minutes at 90 °C, and the final fraction after
60 minutes at 120 °C. The more volatile PAHs were recovered during the first of the
three fractions collected, at 85-125% efficiency. The higher molecular weight PAHs
required longer extraction time, but were all quantitatively recovered (>95%) by the end
of the second fraction, except benzo[a]pyrene. Furton and Rein (1992) noted that SF E of
small quantities of analytes from solid matrices may be diffusion controlled rather than
solubility limited, but the relative importance of diffusion and solubility are highly
dependent on the analyte and matrix being extracted.

The conclusion drawn from the literature reviewed is that the effects of
temperature and pressure are highly dependent on the matrix from which the analyte is
being extracted and on the type of analyte being extracted. TPHs were extracted
efficiently from soil SRS103-100 at low temperatures and high pressures. PAHs can be
extracted from sand, glass beads, Tenax, and similar non-reactive materials with moderate

temperatures and high pressures. In this case, the limiting factor is the solubility of the

13

PAHs, if present at high concentrations. If the PAHs are on soil, river sediment, or air
particulates it may be necessary to increase the temperature of the extraction to desorb the

analyte from the matrix, because in this case the PAHs may be diffusion limited.

2.2 Matrix Effects

The matrix from which the sample is being extracted plays a critical role in the
development of an effective SF E method. To accomplish a rapid extraction, the
optimization process should consist of two steps. First, the extraction conditions of
pressure, temperature, and/or co-solvent need to be optimized to ensure that retention of
the target analytes on the matrix does not occur; this is termed the elution process
(Pawliszyn, 1993). The key to this first step is to ensure that the solubility of the analyte
in the supercritical fluid is high compared to that in the matrix. This will prevent the
analyte from partitioning back onto the matrix at the fluid-matrix interface. Second,
further optimization must be made to ensure that rapid mass transfer of the analytes from
the matrix to the fluid can occur; this is termed the desorption process (Pawliszyn, 1993).
The analyte must be desorbed from the matrix and brought into contact with the fluid-
matrix interface. The more that is known about the analyte interactions with the matrix
the easier it will be to make an educated estimate about the optimization procedure.

Consideration must be made as to how the analyte is associated with the matrix. If
the analyte is at or near the surface of the matrix, the supercritical fluid will have adequate
contact with the analyte and solubility will most likely be the limiting factor. If the analyte

is entrained within crevices, voids, or adsorbed within the matrix, the extraction may take

14

more time and be dependent upon desorption. When analytes are encapsulated within the
matrix only a small fraction of solvent will reach these sites and the sample may need to be
broken up or disrupted so that the solvent can reach the analyte (Pipkin, 1992). Soil and
air particulate matter contaminated with PAHs are good examples of how an analytes
association with the matrix is dependent on the type of media that is contaminated. PAH
contamination of a soil most likely occurs by spilling or placing the contamination on the
existing soil resulting in the PAHs being associated with the surface of the soil particle.

As air particulates form they are contaminated by PAHs from vehicular exhaust and the
PAHs are entrained within the particle and on the surface (Langenfeld, 1993).

The presence of water also affects the extraction of analytes. Water may help or
hinder the process depending on whether the analyte is polar or nonpolar. Water will help
bring polar compounds into solution by competing for active matrix sites, but water may
hinder the extraction of nonpolar compounds by sheathing the surface of the matrix and
acting as a barrier to supercritical fluid penetration (Pipkin, 1992). The affect of water is
also dependent on whether the water is acting as a wetting or non-wetting fluid, which is
dependent on the surface of the matrix.

Burford et al. (1993) studied four different spiking procedures to try to mimic the
native PAHs in a real world sample, but none of the procedures were completely
successful. The interactions of the spiked PAHs and the native PAHs with the matrix
were different because of the aging process and solvents used to introduce the spiked
PAHs. Although the spiking procedures do not mimic the real world sample, extracting

spiked analytes from a matrix can provide usefirl information. To determine whether the

15

limiting process is elution or desorption a standard solution of selected deuterated PAHs
(d-PAHs) can be spiked onto a sample matrix and be extracted along with the native
PAHs (Levy, 1992). The native PAHs undergo both the desorption and elution processes,
because the contaminants have had time to adsorb and interact with the active sites of the
matrix. The spiked d-PAHs will only undergo the elution process. Levy et al. (1992)
determined through the above process that extraction efficiencies of PCBs from river
sediment and low molecular weight PAHs from urban air particulate matter are primarily
limited by the slow desorption process of the analytes from the matrix. The extraction
efficiencies of the PAHs and PCBs showed a dependence on the modifier identity, which
indicates that either the desorption was enhanced or readsorption was prevented, possibly
by competing for active matrix sites. Work conducted by Langenfeld et al. (1993) using
the same samples as used by Levy et al. (1992) showed that increasing temperature was
much more important than increasing pressure. This supports the argument that
desorption is the rate limiting step, because an increase in the temperature would allow the
chemical to overcome the energy barrier of desorption. The increase in pressure would
have increased the solubility of the analytes, but the pressure increase was not as

important as the increase in temperature for improving the extraction efficiency.

2.3 Supercritical Fluids and Modifiers
The main limitation of the most often used supercritical fluid, C02, is its limited
ability to dissolve polar analytes even at very high densities (Levy, 1992). Supercritical

fluid C02 is compatible and miscible with a large range of organic modifiers. The addition

16

of organic modifiers to C02 can overcome solubility limitations. The simplest method of
using modifiers is to add the modifier directly to the sample in the extraction cell.
Modifiers can also be mixed into the supercritical fluid by using an additional pump, which
may mean mechanically altering the SFE apparatus. An alternative is to buy SFE CO;
with the modifier already mixed in the tank of C02 by the supplier. Scott Specialty Gases,
Inc. is one company that will make special order C02 tanks with modifiers. The limitation
with this last alternative is that the modifier type and concentration cannot be changed.

It is important to ensure that the modifier type and concentration will be suitable
for the analysis that is being performed. This will depend on both the analyte of interest
and the matrix from which the analyte is being extracted. A common mistake in selecting
a solvent modifier for SFE occurs when the selection is based on prior experience with
conventional extraction techniques (Pipkin, 1992). A popular modifier that has been used
in many SFE experiments is methanol, but this is not considered to be the best modifier for
all analytes and matrices. Development of the SFE method should take into account the
option of a variety of modifiers that are available for use and the effect of interactions with
the matrix that occur with the analyte and modifier. In addition, derivatization reagents
are available that can be used to increase extraction efficiencies by competing with the
analyte for active sites on the matrix. There is also the option to choose a supercritical
fluid besides CD; that may be better suited for the extraction process.

Hawthorne and Miller conducted experiments to determine the length of time
required to recover PAHs quantitatively from SRM 1650 diesel exhaust particulates using

C02 and C02 modified with 5% MeOH (v/v). The results showed that the supercritical

17
C02/ 5% MeOH extraction of the PAHs was essentially complete during the first 30

minutes (based on the lack of detectable PAH in the 30 to 60 minute sample), while the
extraction using supercritical C02 required 90 minutes (Hawthome, 1986). Ho and Tang
showed poor recoveries of high molecular weight PAHs such as Chrysene,
benzo[a]pyrene, benzo[a]anthracene, and dibenzo[a,h]anthracene when pure supercritical
CO; was used at moderate pressures for extraction from a C18 cartridge (Ho, 1992). The
same high molecular weight PAHs were extracted from an inert matrix (Celite) at
pressures of 300 and 400 atm with pure C02 and quantitative recoveries were obtained in
15 minutes. They concluded that matrix effects were the cause of the low recoveries of
the high molecular weight PAHs from the C18 cartridges. After adding various amounts
of methanol to the extraction cartridge the recoveries were greatly improved and
satisfactory quantitative recoveries were obtained (Ho and Tang, 1992).

Burford et al., did sequential extractions on samples with pure CC; for 30 minutes,
followed by C02 modified with 10% methanol (v/v) for 30 minutes, and finally by
sonication in methylene chloride for an additional 14 hours (Burford, 1993). They found
that the alkanes from the samples were extracted almost completely with the pure C02,
while the native PAHs were found in the pure C02, COz/methanol, and methylene chloride
extracts. The three samples used in this experiment were petroleum waste sludge, SRM
1649 urban air particulate matter, and railroad bed soil. The COZ/methanol extraction
yielded recoveries >8 5% of the native PAHs from the air particulate matter and railroad
bed soil, but not from the petroleum waste sludge. PAH solubility was not the major

limiting factor in the extraction process, as the majority of the spiked d-PAHs could be

l8

quantitatively recovered (>85%) from the petroleum waste sludge and urban air
particulate matter using pure C02, whereas only about 25-75% of the native PAHs were
recovered (Burford, 1993). It was concluded that the modification of the C02 with
methanol increased the extraction rates by increasing the polarity of the supercritical fluid
and by increasing its ability to interact with the matrix to compete with the analyte for
matrix active sites. Langenfeld et al. (1994) tested nine different CO; and organic
modifier mixtures to recover PAHs from urban air particulate matter. The type of
modifier proved to be more important than the modifier concentration for increasing
extraction efficiency. Shown in Table 2.4 are the results of the extraction efficiencies of
PAHs from air particulate matter for two of the modifiers tested at different modifier
concentrations. Although there is no definite theory that explains modifier selection for
SF B, it appears that modifiers should be selected on the basis of matrix characteristics and
the target analyte (Langenfeld et al., 1994).

The option of using a derivatization agent may be attractive when the analyte of
interest is bound tightly to the matrix from which it is being extracted. The derivatization
agent has the capability to displace the analyte from the matrix. Hills and Hill added
commercially available derivatization reagents to two standard reference materials prior to
SFE with CO; to evaluate for the analytical determination of PAHs. The addition of
hexamethyldisilane (HMDS) and trimethylchlorosilane (TMCS) as a 2:1 mixture was
found to enhance the extraction efficiency of PAHs from National Institute of Standards
and Technology (NIST) standard reference material (SRM) 1649 and National Research

Council of Canada (NRCC) SRM HS-3 (Hills, 1993). Hills and Hill used four sample

 

Supercritical Fluid Extraction Efficiencies Using Different
Modifiers and Modifier Concentrations

 

19

Table 2.4

 

« ~2 - d ..
E .- - . :1/0 —.i
. .L: :;“:;.if‘:;;: . - -' -: :- z. 5 ..
. y, -_-,', .

 

 

 

 

 

 

 

 

 

 

 

phenanthrene 4 5 (7) 85 (4) 90(4) 89 (3) 100 (2)
fluoranthene 7.1 (7) 79(6) 83 (5) 82 (4) 96(2)
pyrene 7.2 (7) 64 (6) 70 (5) 66 (3) 81 (2)
benz[a]anthracene 2.6 (12) 63 (7) 78 (3) 67 (11) 94 (4)
Chrysene + triphenylene 5.3 (5) 62 (10) 77 (2) 59 (6) 9o (4)
benzo[b,k]fluoranthene 8.2 (5) 56 (1 1) 87 (8) 60(3) 108 (8)
benzo[a]pyrene 2.9 (17) 18 (16) 41 (4) 20 (8) 60 (8)
benzo[ghi]perylene 4.5 (24) 6(8) 18 (9) 6(3) 26 (1 1)
indeno[123-cd]pyrene 3.3 (15) 9(9) 39 (13) 10 (5) 57 (13)

 

 

 

 

 

 

*Results shown as percent recovery of certified concentration

"The number in parentheses indicates the percent relative standard deviation (%RSD)

 

20

compounds, phenanthrene, fluoranthene, pyrene, and Chrysene, and found that the reactive
modifier increased the extraction efficiency by six times over that of pure C02 and by two
times over that of C02 modified with 10% methanol.

Hawthorne and Miller tested a variety of supercritical fluids to determine their
effectiveness for extracting PAHs from three common environmental solids; urban dust,
fly ash, and river sediment. Supercritical N20 with 5% methanol modifier gave the best
recoveries of PAHs from all three samples when compared to supercritical C02 with 5%
methanol, N20, C02, and ethane (Hawthorne, 1987). The poorest recoveries were
obtained when either ethane or pure CO; were used for the extractions. N20 without
modifier provided better recoveries than ethane or C02, but the addition of methanol as a
modifier increased the extraction efficiencies when CO; or N20 were used. In most cases,
30-60 minute extractions of the river sediment and fly ash with supercritical N20/5%
methanol gave better recovery of the deuterated PAH spikes than the recoveries obtained
by using 4 hours of sonication or 8 hours of Soxhlet extraction with either benzene or
methylene chloride (Hawthome, 1987).

In SFE, matrix interactions with both solvent and analyte exert a powerfiil
influence on the extraction process and must always be considered when selecting a
solvent (Pipkin, 1992). The effect that the modifier has on the supercritical fluid must also
be considered, especially when working at moderate temperatures and pressures.
Depending on the modifier identity, the nature of the analytes of interest, as well as the

type of sample matrix, there is a need to apply an equilibration period when using

21

modifiers in SFE (Levy, 1992). If the modifier does not have sufficient contact time with
the matrix and analyte the firll effect of the modifier may not be achieved. This can
especially be a problem when adding modifiers directly to the extraction cell instead of
mixing the modifier into the supercritical fluid. The modifier can be displaced from the
extraction vessel by the supercritical fluid and end up in the collection vial before it can

interact with the matrix.

2.4 Analyte Collection

When using the SFE on-line with another instrument there is no sample handling,
but if using the SFE in the off-line mode there are many options for sample collection.
After optimizing the SFE to extract the analyte from the sample, the next step for off-line
analysis, is to make sure that the method of sample collection is efficient. The analyte
collection techniques that will be discussed below include collection in an empty vial, a
vial with organic solvent, and a cryogenically cooled trap. The analyte of interest, the
flow rate of C02 during extraction, and the type of analysis to be used after collecting the
sample are some of the variables that will have a bearing on which collection method is
employed.

Miller et al. (1993) conducted experiments to determine the effectiveness of using
an empty vial for the collection of a variety of compounds. They developed a method that
does not use a flow restrictor by collecting the analytes in an empty vial after a static
extraction. Once the static extraction was complete the CO; was depressurized through a

178 um i.d. stainless steel tube into a capped vial that had a single hole punctured in the

22

septum with a 1/16 inch stainless steel rod. The compounds that were tested included
alkanes (Cs-€30), PAHs, PCBs, gasoline, and diesel fiiel. The alkanes > Cm were
recovered at 96-99% and the C6-C9 alkanes had recoveries of 39, 70, 88, and 94%,
respectively. The PCBs recoveries for the di- through hepta—chloro congeners ranged
from 90-97%. Efficient recoveries of the PAHs proved to be more difficult than the
alkanes and PCBs, but it was mainly due to the PAHs not being extracted from the matrix.
Initially, the low molecular weight PAHs were recovered at >90%, but the larger
molecular weight PAHs chrysene and benzo[b]fluoranthene showed recoveries of 60 and
74%. When the spiked sand was extracted sequentially three times, the recoveries of the
two higher molecular weight PAHs were increased to 84 and 82%. The recovery of
gasoline hydrocarbons (TPH) was 73% and recovery of diesel fuel hydrocarbons (TPH)
was 92%.

Studies were done by Lopez-Avila et al. (1992) on the use of organic solvents for
the off-line collection of petroleum hydrocarbons from various soil samples after SF E.
The organic solvents tested included Freon-113, perfluorohexane, hexafluorobenzene,
Flon S-316, carbon tetrachloride, and PCE. The collection solvent for the extracted
material must be compatible with the IR detemrination, and it should have the solubilizing
properties of Freon-1 13, be nonflammable, nontoxic, have a boiling point higher than 100
°C (so that little will be lost through volatilization during the carbon dioxide
depressurization step), and a freezing point below -30 °C (which is the typical temperature
of the collection solvent during the 30 minute extraction when no heat is applied to the

collection vial) (Lopez-Avila, 1992). The perfluorohexane had poor solubilizing

23

properties for the analytes of interest compared to Freon-113, but it was a good solvent
because 80% remained after bubbling carbon dioxide through it for 30 minutes at a flow
rate of 1 ml/min (as liquid). The hexafluorobenzene cost was too high so it was eliminated
immediately, hexafluorobenzene is $1780/L whereas Freon-l 13 is only $3 8/L. Flon S-3 16
(a tetrachloro-hexafluorobutane) had only 14% volatilization afier carbon dioxide had
been bubbled through it for 60 minutes at the same flow rate mentioned above. It is a
good solvent for hydrocarbons, but it is about five times more expensive than Freon-113.
Carbon tetrachloride worked well as a collection solvent, but it is listed by the EPA as a
probable carcinogen, and thus its use is generally not recommended. PCE is an even
better solvent than Freon-113 for petroleum hydrocarbons containing 30 or more carbon
atoms. It proved to be a good collection solvent and was compatible with the IR analysis
as well. As a result of the study, Lopez-Avila et.al., recommended PCE as a collection
solvent for TPHs.

Ashraf—Khorassani et al. (1992) carried out studies comparing an empty vial, a vial
with solvent, and a cryogenic trap as methods of collection after SFE. Initially, they
extracted a mixture of phenanthrene and pyrene and collected the analytes with each of the
three methods for off-line collection. The collection efficiency using the empty vial was
very low, but recoveries were improved when methylene chloride was added to the vial.
Others have reported good collection efficiencies using organic solvents, but it should be
noted that the flow rates were relatively low (< 1 ml/min). The flow rate in this study was
2 ml/min and it is thought that the loss of analyte in the solvent filled vial was due to the

formation of an aerosol. Collection efficiencies of greater than 90% were observed when

24

a cryogenically cooled trap was used. The high percent recovery obtained with a
cryogenically cooled adsorbent trap is due to two factors: (a) freezing the analytes in the
trap upon decompression, and (b) retaining the analytes on a bed of silanized glass beads.
Two wash solvents used to rinse the analytes from the cryogenic trap were also compared.
Lower percent recoveries were obtained when methanol was used as compared to the
recoveries obtained when methylene chloride was used as the wash solvent. The effect of
the temperature of the cryogenic trap on collection efficiency of aliphatic hydrocarbons
was also evaluated. A temperature of -45 °C compared to -20 °C increased the efficiency
of decane trapping, but the collection efficiency of the rest of the test compounds
remained unchanged. For volatile compounds the trap temperature is an important
parameter that will affect collection efficiencies. Overall, the cryogenic trap was much
more effective than the empty vial or solvent filled vial. Also, the flowrate of C02 through
the extraction vessel did not have any effect on the collection efliciency of the cryogenic

trap.

CHAPTER 3

METHODOLOGY

3.1 SF E Apparatus

A Suprex PrepMasterTM and AccutrapTM SFE with cryogenic collection purchased
from the Suprex Corporation, Pittsburgh, PA, USA, was used throughout this research
project. The SFE had the capability of reaching pressures of 500 atm and temperatures of
150 °C for the extraction of samples. A 3 ml stainless steel extraction vessel was used for
all of the extractions. The restrictors used were stainless steel and were kept at 150 °C to
prevent plugging. The SFE C02 used had helium headspace and 1.0% MeClz modifier,
purchased from Scott Specialty Gases, Inc., Plumsteadville, PA, USA. The nitrogen used
for purging the cryogenic collection trap was purchased from AGA Gas Inc., Cleveland,
OH, USA. Also purchased from AGA was C02 with a siphon, which was used to control

the collection trap temperature.

3.2 Quantitative and Qualitative Analysis

Two instruments were used for the qualitative and quantitative analysis of the
samples collected from the SFE. A Hewlett-Packard GC/MS was used for qualitative
analysis, Hewlett-Packard, Palo Alto, CA, USA. The GC was a 5890 Series and the MS

was a 5972 Series. The mass spectrometer was operated in the scan mode and a mass

25

26

range of 10 to 500 atomic mass units (amu) was scanned. The column used was a HP-S
M.S. (Hewlett-Packard, Palo Alto, CA, USA) that was 30 m long and had a 0.25 mm ID
and a 0.25 um film thickness. The initial column temperature was 60 °C and the final
column temperature was 300 °C. The temperature program ramped the column
temperature from 60 °C to 300 °C at a rate of 5 °C/min. The column was held for 2.0
minutes at 60 °C before the temperature ramp was begun and also held for 2.0 minutes at
300 °C at the end of the temperature ramp. The injector was held at a constant
temperature of 250 °C.

Varian 3400 GC/FID with a Varian 8100 Autosampler was used for the
quantitative analysis (Varian, Walnut Creek, CA, USA). The column used was a Supelco
SPBm-S that was 30 m long and had a 0.53 mm ID and 0.50 pm film thickness (Supelco,
Inc., Bellefonte, PA, USA). The initial column temperature was 60°C and the final
column temperature was 300°C. The temperature program ramped the column
temperature from 60°C to 300°C at a rate of 8°C/min. There was no initial hold time at
60°C, but the column was held at the final temperature of 300°C for 20 minutes. The
injector had an initial temperature of 30°C and was held initially for 0.2 minutes before the
100°C/min temperature ramp program started. . The final injector temperature was 320°C
and was held at that temperature for 46.9 minutes. The FID was held at a constant

temperature of 320°C.

27
3.3 Reagents

Solvents used with the SFE were methylene chloride (GC Resolv) and methanol
(HPLC Grade) and were obtained from Fisher Scientific, Pittsburgh, PA, USA. Solvents
used for the Soxhlet extractions included the same grade methylene chloride as mentioned
above as well as cyclohexane (HPLC Grade) and pentane (Capillary GC/GC-MS Solvent)
both of which were purchased from Baxter Diagnostics Inc., Mc Gaw Park, IL, USA.
The extraction thimbles used were Whatman 43 mm x 123 mm single thickness cellulose
extraction thimbles (Whatman International, Ltd, Maidstone, England). The Soxhlet
extraction clean-up procedure required the use of sodium sulfate (Anhydrous Granular 12-
60 mesh, J .T. Baker Inc, Phillipsburg, NJ, USA) and silica gel (Davidson 923 100/200
mesh, Supelco, Bellefonte, PA, USA). The PAH standard used for GC calibration curves
was the Supelco TCL Polycyclic Aromatic Hydrocarbons Mix with 2000 rig/ml of each
PAH in methylene chloridezbenzene (50:50). PAHs used to spike soils were naphthalene,
phenanthrene, pyrene, and benzo[a]pyrene. The naphthalene (99%) and benzo[a]pyrene
(98%) were purchased from Sigma Chemical Company, St. Louis, MO, USA and the
phenanthrene (98%) and pyrene (99%) were purchased from Aldrich Chemical Company,

Inc, Milwaukee, WI, USA.

3.4 Soil Characteristics
Three materials were used in this study: Ottawa Sand, Soil A, and Soil C. The
mechanical characteristics of the soils are shown on Table 3.1. The Ottawa Sand was

used as an inert material from which PAHs could be extracted. Soil A was a clean,

28

uncontaminated horizon A from a site near Collins Road and Forest Road in Lansing, MI,
USA. The Soil A was used to test the extractability of PAHs from a matrix that was more
representative of a real world matrix than the Ottawa Sand. There were two methods
used to spike known amounts of PAHs onto the soil: (1) PAHs were spiked onto the soil
just prior to extraction (fresh spike), and (2) PAHs were spiked onto the soil and were
then allowed to age for over one year (aged spike). The spiking procedures are described
in the next section of this chapter. Soil C was a soil from a coal tar contaminated site,
which was contarrrinated during the time period from the late 1800’s until approximately
the late 1940’s. Soil C was monitored for 16 PAHs. Appendix A contains physical
characteristics and structures of the sixteen PAHs. The presence of native PAI-Is in the
soil was significant for this research, but in some cases additional PAHs were spiked onto

the soil; both fiesh spike and aged spike.

Table 3.1

Mechanical Characteristics of Soils used in Experiments

 

 

 

 

 

 

 

 

' 3611A 8611c
Organic Matter (%) 10.8 7.8

Sand (%) 81.3 58.6

Silt (%) 12.4 24.0

Clay (%) 6.4 17.4

Soil Type Loamy sand Sandy loam

 

29

3.5 Spiking Procedure

As stated earlier naphthalene, phenanthrene, pyrene, and benzo[a]pyrene were
used as the model PAH compounds for the spiking procedures. The two spiking
procedures, fresh spike and aged spike, were used in this research to introduce the PAHs
onto the soil matrices. The procedure for the fresh spike was to weigh out the soil
sample, place it in the extraction vessel, and then spike the soil sample with the PAHs. An
amount of 200 pl of a stock solution containing 1000 rig/ml of each of the four PAHs in
methylene chloride was added to the soil sample in the extraction vessel. The extraction
vessel was then immediately connected to the SFE and the extraction procedure carried
out. An amount of 4.0 grams of Ottawa Sand was used for the fresh spike extractions of
PAHs from the sand matrix. For both Soil A and Soil C, an amount of 2.0 grams of freeze
dried soil was used for the fresh spike extractions.

The aged spike consisted of adding the four model PAHs to 100 grams (dry
weight) of soil to obtain a concentration of 200 u g of each PAH] g of dry soil. The stock
solution used to spike the soil contained approximately 1000 rig/ml of each PAH in a
50:50 (v/v) mixture of methylene chloridezbenzene. The concentrations of the PAHs in
the stock solution were determine by GC analysis and the results are shown in Table 3.2.
Afier adding the stock solution to the soil, the methylene chloride and benzene were
allowed to volatilize from the soil over a 16 hour time period. The samples were stored in
glass bottles, placed in a refiigerator at 4 °C, and protected from exposure to light. The

first month the samples were shaken once a week to mix the soil with the spiked PAHs.

30

The samples were shaken once every two or three months for the remainder of the aging
process. The samples were not used for any extraction procedures until over 15 months
of aging time. For both Soil A and Soil C aged spike samples, an amount of 2.00 grams of
freeze dried soil was weighed out, placed in the extraction vessel, and the extraction

process carried out.

Table 3.2
Concentration of PAHs Added to Soil A and Soil C for the Aged PAH Spike

l Concentration * " ’ ‘ ' ' ’

   

 

 

 

 

 

 

P (ugongofdsmI) ' '
Naphthalene 220 i 15
Phenanthrene 220 i 14
Pyrene 220 :1: l6
Benzo[a]pyrene 200 i 11

3.6 SF E Procedure

The SFE conditions used for the extractions are listed in Table 3.3. The pressure,
temperature, and extraction time were variables that changed depending on the experiment
being conducted. The pressures used for the extractions ranged from 200 to 400 atm and
the temperatures ranged from 60 to 150 °C. The dynamic extraction times ranged fi'om 5
to 45 minutes. Specific information about the pressure, temperature, and extraction time
will be provided along with the results for each of the experiments conducted. The
extractions were performed in triplicate and standard deviations are provided with the

results.

 

Table 3.3

SFE Conditions used for the Extraction of PAHs from the Soil Matrices

 

 

 

 

 

 

 

 

Prepmaster Method

Pressure varied
Temperature varied
Extraction Time varied
Extraction Vessel Size 3 ml
Accutrap Method

Collection Temperature -20 °C
Desorption Temperature 15 °C

 

Desorption Rinse

3 ml of methanol
at 1.0 ml/min

 

 

 

Flush Temperature 15 °C

Flush Rinse 5 ml of methanol
at 1.0 ml/min

Restrictor 150 °C

3.2 ml/min flowrate

32

In some cases, the organic modifier concentration was increased by adding
methylene chloride directly to the soil sample in the extraction vessel. When additional
organic modifier was added to fresh spike extractions an amount of 500 pl of methylene
chloride was added. This resulted in a total of 700 pl of methylene chloride being added
to the soil; 200 pl of methylene chloride from the PAH stock solution plus the additional
500 111 of methylene chloride. When organic modifier was added to the aged spike
samples, an amount of 700 pl of methylene chloride was added to the soil. It was
assumed that the solvent used to spike the PAHs onto the soil had volatilized from the
aged spike soil samples. This assumption was based on the fact that the solvents were
allowed 16 hours to volatilize from the soil afier spiking the PAHs onto the soil.

Ottawa Sand was used as an inert material from which PAHs could be extracted
using SFE with C02 modified with 1% methylene chloride. The extractions carried out
with the sand were useful for determining whether the SFE was firnctioning properly. The
extraction efficiencies of the PAHs from the sand, at specific operating parameters, were
used as a QA/QC check on the SFE system. The QA/QC extractions were done at
various points during the research to ensure that the results obtained were not a result of
the SFE firnctioning improperly. The reason for starting a QA/QC protocol was because
of problems encountered at the beginning of the research project. Extraction recoveries of
PAHs from the Ottawa sand were low at first. There were four problems found with the
SFE that needed to be addressed before any data could be collected.

First, the nitrogen purge line for the cryogenic trap was fixed, because it was not

hooked up correctly. The ferrule on the nitrogen inlet line to the SFE was not seated

33

properly and the rinse solvent in the cryogenic trap was not being expelled into the
collection vial. Second, the vent line on the SFE that releases the pressure from the
system between the restrictor and the extraction vessel was plugged. When the dynamic
extraction is completed, the manifold switches the SFE back to the static mode. There
continued to be a volume of pressurized C02 behind the restrictor that was trying to exit
the system and the only path for it to take was through the cryogenic trap. This resulted
in excessive gas flow into the collection vial while the rinse solvent was being dispensed
and caused some of the rinse solvent, and PAHs, to enter the vent line of the collection
vial. It may also have contributed to the volatilization of naphthalene, which showed the
poorest recovery.

Third, the temperature of the cryogenic trap during the desorption and flushing
stage was lowered from 40 °C to 15 °C. This was done after talking to a representative at
Suprex about the problems encountered with the recovery efficiencies. The representative
mentioned that the restrictor temperature (150 °C in this case) may cause the solvent to
vaporize. If the cryogenic trap temperature is not low enough to cool the solvent back
down then it may still be in the vapor form as it goes through the trap. Finally, the rinse
solvent was changed fi'om methylene chloride to methanol. The amount of methylene
chloride being dispensed during the trap rinsing was not precise because the seal on the
pump was not compatible with methylene chloride. The pump had to be taken apart and
the methylene chloride evaporated from the seal. This allowed the pump to fiJnction
properly again, although only for a limited time. Methanol will not cause any problems

with the pump, but the solubility of PAHs in methanol is lower than it is in methylene

34

chloride. This may or may not cause problems in the fiJture when trying to rinse analytes

from the trap, and should be taken into consideration if recoveries are low.

3.7 Soxhlet Extraction Procedure

A general description of the Soxhlet extraction procedure is described below. A
more detailed, step-by-step set of instructions are given in Appendix B. Soil samples were
weighed out, placed in extraction thimbles, and freeze dried for 12 to 16 hours. The
Soxhlet extraction of the samples was conducted for 16 to 20 hours using 300 ml of
methylene chloride and were done in triplicate. After the extraction was complete, an
amount of 200 ml of cyclohexane was added, and the methylene chloride was boiled off.
The cooled sample was then poured through a drying column containing silica gel and
sodium sulfate. The column of silica gel was rinsed with 60 ml of pentane to displace the
cyclohexane from the column. The analytes were then removed from the silica gel using a
60:40 (v/v) mixture of pentanermethylene chloride and collected in a flask. The
concentration step was then carried out using a water bath at 65 - 70 °C to boil off the
solvents. Methylene chloride was then added to a specific volume, the sample transferred

to GC vials, and stored at 4 °C until the analysis could be performed.

CHAPTER 4

PAHs EXTRACTED FROM OTTAWA SAND

4.1 Temperature and Pressure Effects

The next set of extractions carried out, using Ottawa Sand as the media, tested the
effect of using different temperatures and pressures on the extraction efficiency for PAHs.
The total dynamic extraction time was 10 rrrinutes. An amount of 4.0 grams of Ottawa
Sand was placed in the 3 ml extraction vessel and spiked with 200 pl of PAH stock
solution. The recoveries from the sand were compared to the concentration of the PAH
stock solution, both of which were determined by GC analysis. Temperatures of 120 °C
and 150 °C were tested with three different pressures of 200, 300, and 400 atm (Table 4.1
and Table 4.2). A pressure of 300 atm was used to test the effect of four temperatures:
60, 90, 120, 150 °C (Table 4.3).

The results of varying the pressure during the extraction at 120 °C showed that
changing the pressure does not have a large effect on recovery efficiency for this matrix.
All of the PAHs were recovered with efficiencies > 89%, with the exception of the
benzo[a]pyrene when the SFE pressure was 200 atm. The recovery of benzo[a]pyrene
was only 70% at 200 atm, but the standard deviation between the three extractions was

relatively high compared to the rest of the results.

35

36

Table 4.1

Percent Recovery with Varying Pressure at a Constant Temperature of 120 °C

' T991800   '7 i.

g
- 159998992

120 " ’ ’ “

PWSSW' "(WW-331i 900‘ 5 ~ - : ‘

Standard f 7
I 0998999 ’

‘ “ 120 ’
.300 ~
iAverage »
899mm ;

Standard .,
: LDeViatiQIl; .5

. Average A
,Recovery .i

* 120

71.5 Standard

: Deviation f;

 

 

Naphthalene

93

94

89

 

Phenanthrene

96

101

99

 

Pyrene

97

103

100

 

 

 

 

Benzo[a]pyrene

 

70

 

 

105

 

bWWL/I

103

 

 

 

Table 4.2

Percent Recovery with Varying Pressure at a Constant Temperature of 150 °C

Empire) “

,1 13835511119, (atm) i, ‘

3mg

“5:150 '

200

"Recovery .'

eévsztanW»;

,‘Deviation, ,

”1‘50
. .300 m w

Average  -

, Standard... 7 3
”Deviation ; -' '-

* 9 Standard
Deviation;

 

 

Naphthalene

84

88

\O

15

 

Phenanthrene

98

99

7

 

Pyrene

98

Ar—ON

103

8

 

 

Benzo[a]pyrene

 

 

81

O

113

 

 

MAUI

 

 

l4

 

37

Table 4.3

Percent Recovery with Varying Temperature at a Constant Pressure of 300 atm

1

 

 

 

 

 

 

Pressure (atm) f _ 300 — 300g 373‘ 300 . ’_ 300
I 1 Avg Recovery Avg Recovery Avg Recovery Avg Recovery}
KL 3‘}: .. iStd Dev :1: Std Dev :1:- Std Dev ,9; Std Dev. ,
Naphthalene 97 i 9 101 :1: 18 94 :t 5 88 i 19
Phenanthrene 102 i 1 103 i 2 101 d: 3 99 :1: 5
Pyrene 104i2 103i1 103i3 103i4
Benzo[a]pyrene 102 i 6 109 i 7 105 a: 4 113 i 5

 

 

 

 

The recovery of the PAHs increased slightly when the temperature was increased
to 150 °C. A statistical analysis using the Student t test with a 95% confidence interval
was done and there was no statistical difference in the recoveries obtained at pressures of
300 or 400 atm pressure. Both of the higher pressures resulted in a statistically significant
increase in the recovery of benzo[a]pyrene compared to the recovery obtained when 200
atm was used.

When the pressure was held constant at 300 atm and the temperature was varied
there was no change in recovery of any of the PAHs. Recoveries were all >94%, with the
exception of the naphthalene recovery being 88% when the conditions were 300 atm and
150 °C. However, there was no statistical difference in the recovery of naphthalene
obtained when either 120 °C or 150 °C were used.

These results indicate that the PAHs are not limited by solubility at the

concentrations that were spiked onto the sand. An amount of 4.0 grams of sand was used

 

38

for the extractions and 200 111 of PAH stock solution was added to the sand. The stock
solution concentration contained 1000 ug/ml of each of the four model PAHs, therefore

200 ug of each PAH was extracted using C02 modified with 1% methylene chloride.

CHAPTER 5

PAHs EXTRACTED FROM SOIL A

5.1 Extractions of Fresh Spike using 90 °C and 300 atm

PAHs were extracted from Soil A after adding PAHs to this matrix using the fresh
spike technique. The SFE conditions are shown in Table 5.1. Note that the collection of
the analyte was fractionated in order to plot the rate of analyte recovery versus time
(Figure 5.1). The overall PAH recovery was >87% for naphthalene, phenanthrene, and
pyrene, but the recovery of benzo[a]pyrene was only 66% (Table 5.2). The predominant
difference in the recovery of the PAHs from Soil A as compared to that observed with
Ottawa Sand is that the benzo[a]pyrene was not as easily extracted in Soil A. It only took
10 minutes to quantitatively recover the benzo[a]pyrene from the Ottawa Sand, but afier a
30 minute extraction of Soil A the benzo[a]pyrene was recovered at less than 70%. Since
solubility was not a problem, it is believed that the slow desorption of the benzo[a]pyrene

from Soil A limits the extraction efficiency.

5.2 Extractions of Fresh Spike using 150 °C and 300 atm

The temperature of the extraction was increased to 150 °C to try to the efficiency

at which benzo[a]pyrene can be extracted from Soil A. All other experimental conditions

39

40

Table 5.1

SFE Conditions used for the Extraction of Fresh Spike PAHs from Soil A

 

 

 

Prepmaster Method
Pressure 300 atm
Temperature 90 °C

 

Extraction Time

1 min Static

5 min Dynamic
5 min Dynamic
10 nrin Dynamic
10 min Dynamic

 

 

 

 

Extraction Vessel Size 3 ml
Accutrap Method

Collection Temperature -20 °C
Desorption Temperature 15 °C

 

Desorption Rinse

3 ml of methanol
at 1.0 ml/min

 

Flush Temperature

15°C

 

 

Flush Rinse 5 ml of methanol
at 1.0 ml/min
Restrictor 150 °C

3.2 ml/min flowrate

41

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42

Table 5.2

Percent Recovery of PAHs from Soil A with the SFE at 90 °C and 300 atm

     

 

 

 

 

 

 

 

 

Emacuon . — * ~ .

gTimMmini :5 w z 20 30
Naphthalene 77 d: 13 87 i 6 87 i 5 87 3: 5
Phenanthrene 80 i 12 92 :1: 7 93 2t 5 93 i 5
Pyrene 74 d: 10 89 :t 6 94 i 3 94 :t 3
Benzo[a]pyrene 40 i 5 52 d: 6 64 i 6 66 d: 6

 

 

were the same as listed in Table 5.1. The result was that the naphthalene, phenanthrene,
and pyrene were recovered at efficiencies of >94%, but the recovery efficiency for
benzo[a]pyrene remained only 62% (Table 5.3). The standard deviation between the
triplicate samples decreased for all of the compounds except benzo[a]pyrene. The rate of
extraction was increased slightly for all the compounds except benzo[a]pyrene (Figure

5.2).

5.3 Extractions of Fresh Spike using an Organic Modifier

Since the benzo[a]pyrene was not extracted satisfactorily by increasing the
temperature, an organic modifier was added to the extraction cell and the temperature was
reduced to 90 °C. The supercritical fluid C02 already had 1% methylene chloride mixed
into the gas cylinder and methylene chloride was used as a solvent for the PAHs spiked

into the soil. Therefore, methylene chloride was chosen as the organic modifier to be

 

43
Table 5.3

Percent Recovery of PAHs from Soil A with the SFE at 150 °C and 300 atm

 

 

 

 

 

 

 

 

 

 

Extraction 975::  ’ A » ‘ ? i- y . ‘ ‘ i . : -» _ . - . . ‘
Naphthalene 92 i 3 97 :1: 3 97 i 2 97 :1: 2
Phenanthrene 88 :t 6 95 :t 3 95 :1: 3 95 :t 3
Pyrene 80i8 922t5 94i3 943:3
Benzo[a]pyrene 40 i 10 51 i 11 59 :i: 11 62 i 9

added directly to the extraction cell. An amount of 500 111 of methylene chloride was
added immediately after the 200 111 PAH spike was added to the soil. The extraction cell
was then attached to the SFE for extraction. The result was that the benzo[a]pyrene was
extracted at a recovery of 99% (Table 5.4). The phenanthrene and pyrene were recovered
at >100% and the naphthalene was recovered at 89%. The rates of recovery were also
improved greatly when the organic modifier was added to the extraction cell (Figure 5.3).
The phenanthrene and pyrene were completely recovered after the first 5 minute dynamic
extraction step. The naphthalene and benzo[a]pyrene had 89% and 94% recoveries after a

total of only 10 minutes of dynamic extraction time.

5.4 Extractions of Aged Spike using 90 °C and 300 atm
In experiments in which the PAHs were to be extracted from the aged spiked Soil
A the SFE conditions were the same as those listed in Table 5.1. An amount of 2.0 grams

of the aged spike Soil A was placed in the extraction cell for the analysis. The recoveries

 

44

of phenanthrene and pyrene were 80% and 87%, respectively. Naphthalene and

benzo[a]pyrene were not recovered very efficiently with only 33% and 38% recoveries,

respectively (Table 5.5). Also, the rate of extraction was slower for the aged spike than

for the fresh spike (Figure 5.4).

The naphthalene recovery may be better than the calculated value, because the

percent recovery was based on the amount of naphthalene spiked into the soil and not the

actual amount of naphthalene lefi in the soil after one year. After it was spiked with the

PAHs, the soil sample was left open to the atmosphere overnight to allow the solvent to

evaporate from the soil. It is likely that some of the naphthalene volatilized and was lost

from the sample. It is also possible that some of the naphthalene was degraded during the

aging process by microorganisms present in the soil. An indication that the actual

Table 5.4

Percent Recovery of PAHs from Soil A with the SFE at 90 °C and 300 atm
with 500 pl of Methylene Chloride Added as an Organic Modifier

 

 

 

 

 

 

Cumulauve a   , y y e """"

Extraction "i “ .' ‘ f * ’-
Trrne(mln) 3:5 f '10: is 220' . p» i 30
Naphthalene 87 :t 3 89 i 4 89 :1: 4 89 d: 4
Phenanthrene 101 :t 1 104 :1: 2 104 d: 2 104 :1: 2
Pyrene 101i 2 1073:] 107 i] 107i]
Benzo[a]pyrene 86 i 7 94 i 5 98 a: 4 99 :1: 4

 

 

 

 

 

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47

Table 5.5

Percent Recovery of PAHs from Aged Spike Soil A with SFE at 90 °C and 300 atm

Ex“ L ~:  2: .. , . ; :. : . a +.. ~ -_ ,,,,, ; ~ .; ~  ...: . i ; e ~ -- . i . 1 , -

 

 

 

 

 

 

 

 

 

 

Naphthalene 25 i 2 30 fl: 1 32 :1: 1 33 i 1
Phenanthrene 60 :t 5 74 :1: 4 79 :1: 4 80 :t 4
Pyrene 59 d: 5 79 i 4 86 :1: 4 87 i 4
Benzo[a]pyrene 13 d: 2 23 i 3 34 i 4 38 :t: 5

 

concentration may be lower than actually noted is the flattening of the extraction rate
curve for naphthalene in Figure 5.4. In the first 10 minutes of the dynamic extraction it
appears that all of the naphthalene was extracted from the sample. The other compounds,
phenanthrene, pyrene, and benzo[a]pyrene could have been subject to biodegradation as
well, but based on the recoveries and extraction rates it was less likely to be as important
of a factor as it was for naphthalene. The sample was kept in a dark place so that
photodegradation should not have been a factor.

The aged spike Soil A was then analyzed using a Soxhlet method (Appendix B),
which provided a comparison for the SFE method to something other than the theoretical
concentrations of PAHs. The results of the Soxhlet extraction of the one year aged PAH
spike Soil A are shown in Table 5.6. The results indicate that the naphthalene was much
lower than the theoretical value of 220 ug/g of dry soil. The concentrations for the

phenanthrene, pyrene, and benzo[a]pyrene are close to the threoretical values of 220, 220,

48

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49

Table 5.6

Concentration of PAHs Determined by Soxhlet Extraction
in Aged PAH Spiked Soil A

PAH~Ccm<ungAHIgfdryl>

 

Naphthalene 92 i 15

 

Phenanthrene 173 :t 25

 

Pyrene 177 i 27

 

 

 

Benzo[a]pyrene 152 i: 20

and 200 ug/ g of dry soil, respectively. While the small differences in the concentration
values of phenanthrene, pyrene, and benzo[a]pyrene as determined using Soxhlet
extraction and the theoretical values may be due to inefficiencies of the Soxhlet method,
this is unlikely to be true for naphthalene (Table 5.7). If the SFE recoveries are compared
to the Soxhlet recoveries the extraction efficiencies with the SFE at 90 °C and 300 atm are
greatly improved over those calculated by comparing the SFE recoveries to the theoretical
values (Table 5.8). The benzo[a]pyrene recovery remains low and needs to be improved.
The rates of extraction of the PAHs by SFE (relative to the recoveries using Soxhlet

extraction) are shown in Figure 5.5.

 

50

Table 5.7

Percent Recovery of PAHs by Soxhlet Extraction (18 hour extraction time) Based on
Theoretical Concentrations in Aged PAH Spiked Soil A

 

 

 

 

 

 

PAH ‘i , , , Percent Recovery
Naphthalene 4] i 7
Phenanthrene 79 2t 12
Pyrene 81 i 12
Benzo[a]pyrene 77 i 10

Table 5.8

Percent Recovery of PAHs from Aged Spike Soil A with the
SFE at 90 °C and 300 atm Relative to the Soxhlet Extraction Recoveries

 

 

 

 

 

 

 

 

 

 

;Extt99ti9n~w ‘ ' .i ‘. ’
Timetmin) -; i 5'   f 10 - ; ’ 20 _ 30
Naphthalene 59 i 5 73 d: 3 78 i 3 80 i 3
Phenanthrene 76 d: 7 95 i 5 100 i 5 101 i 5
Pyrene 74i6 98i5 106i5 10815
Benzo[a]pyrene 17 i 2 30 i 3 44 :t 5 49 :1: 6

 

 

51

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52
5.5 Extractions of Aged Spike using an Organic Modifier

The addition of an organic modifier to the fresh spike Soil A resulted in an increase
in the extraction efficiency of the benzo[a]pyrene. Therefore, the addition of an organic
modifier was used to attempt to increase the extraction efficiency of benzo[a]pyrene from
the aged spike Soil A. After the sample was placed in the extraction vessel, an amount of
700 u] of methylene chloride was added as an organic modifier. The SFE conditions were
the same as those listed in Table 5.1, with the temperature at 90 °C and the pressure at
300 atm. While the addition of the organic modifier increased the recovery of
benzo[a]pyrene, the recovery was still only 77% based on the soxhlet extraction results
(Table 5.9). The extraction rates of the PAHs increased compared to the rates when no

organic modifier was used at 90 °C and 300 atm (Figure 5.6).

Table 5.9

Percent Recovery of PAHs from Aged Spike Soil A with the
Addition of 700 11.1 of Methylene Chloride as an Organic Modifier
SFE at 90 °C and 300 atm Relative to the Soxhlet Extraction Recoveries

 

 

 

 

 

 

 

 

 

 

Cummulatrve . .. .. . ., .
:EsExrraction: 3 3i, ' w ~ ‘ ‘  ; . ~ . ; .
mom) 5* ‘ ~110 29 ' 30‘
Naphthalene 71 i 6 83 i 5 86 3: 6 86 i 6
Phenanthrene 92i6 110i6 115i6 115i6
Pyrene 95i7 115:1:5 ll7i5 117d:5
Benzo[a]pyrene 59 :1: 5 70 i 5 75 i 4 77 i: 4

 

53

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5.6 Extractions of Aged Spike using an Organic Modifier and 150 °C

54

Since the benzo[a]pyrene recovery remained relatively low the extraction

temperature was raised to 150 °C and methylene chloride was used as an organic modifier.

The extraction conditions were the same as those listed in Table 5.1, with the exception of

the 150 °C temperature. The results show that the benzo[a]pyrene recovery had increased

to >90% (Table 5.10). The extraction rate curves are shown in Figure 5.7. In order to

extract the PAHs from Soil A after one year of aging it was required to raise the

temperature and add methylene chloride as an organic modifier.

Percent Recovery of PAHs from Aged Spike Soil A with the

Table 5.10

Addition of 700 pl of Methylene Chloride as an Organic Modifier
SFE at 150 °C and 300 atm Relative to the Soxhlet Extraction Recoveries

 

 

 

 

 

 

 

 

 

 

i'Cuiri'rfrnulatiVe-i . _ , _ _ ..
ij“EXtr7action * .

Time (min) . 5   10 20 30
Naphthalene 72 i 4 85 :t 4 88 :t 4 88 d: 4
Phenanthrene 105i3 116i4 117d:4 117i4
Pyrene 100i5 ll3:t6 116i7 117i8
Benzo[a]pyrene 70 :t 7 85 i 5 91 i 5 93 i 5

 

55

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CHAPTER 6

PAHs EXTRACTED FROM SOIL C

Soil C was obtained from an actual coal tar contaminated site, but the specific site
description is confidential. The contamination was the result of the disposal of the coal tar
waste in open, unlined pits from a time period between the late 1800’s to approximately
the late 1940’s. The term native PAHs is used to describe the contamination present in
the soil as a result of the disposal of the coal tar. The relevence of Soil C for this research
is that the PAHs have been in contact with the soil for 50 to 100 years. These native
PAHs from the coal tar have had time to interact with the soil matrix and are likely to be
more difficult to extract quantitatively than fresh spike PAHs. PAHs that are spiked onto
soil to develop extraction methods for the quantification of contaminants may not have the
same matrix interaction characteristics as native PAHs. Extraction of spiked PAHs will
usually result in an overestimation of the extraction method efficiency. The advantage of
using spiked PAHs is that the concentration of PAHs is known. If a soil with native PAHs
is used to develop a SFE method the actual concentration of PAHs is not known. For this
research, the native PAH contamination of Soil C was determined by Soxhlet extraction
and the SFE method was compared to the Soxhlet results. The actual efficiency is not

known for either method, because the true PAH concentration is not known.

56

57
6.1 Soxhlet Extraction

Soxhlet extraction was performed on Soil C using the method outlined in
Appendix B. The results of triplicate samples are shown in Table 6.1. There were a total
of 12 PAHs (out of the 16 PAHs included in the Supelco standard) at concentrations high
enough for quantitation. The benzo[b]fluoranthene and benzo[k]fluoranthene peaks co-
eluted and are reported as a total concentration of the the two compounds; the same was
true for indeno[1,2,3-c,d]pyrene and dibenzo[a,h]anthracene. The higher standard
deviations for phenanthrene, fluoranthene, and pyrene are most likely due to greater

baseline noise near their retention times than in other areas of the chromatogram.

6.2 Fractionated Extraction with SFE at 90 °C and 300 atm

The SFE results from Soil A aged PAH spike showed that both organic modifier
and increasing temperature resulted in better recoveries of PAHs. The SFE of native
PAHs from Soil C were conducted using the same series of extraction conditions used to
test Soil A. The series of conditions included 90 °C and 300 atm; 90 °C, 300 atm, and
organic modifier; and 150 °C, 300 atm, and organic modifier. Results should indicate
whether or not the SFE information from Soil A can be used as a template for SF E
method development for Soil C.

The first SFE condition tested was 90 °C and 300 atm with no organic modifier
(Table 6.2). Concentrations determined by SFE were reported as percent recovery based
on the concentrations obtained by Soxhlet extraction (Table 6.3). The rates of extraction

are shown in Figure 6.1. The recoveries of naphthalene and phenanthrene were well over

Table 6.1

Concentration of Native PAHs in Soil C Determined by Soxhlet Extraction

. ; . 991189999999 (.11 OfPAH/ghadryti‘ifli

 

 

 

 

 

 

 

 

 

 

 

 

Naphthalene 1 1 i 3
Phenanthrene 82 i 20
Fluoranthene 75 :1: 15
Pyrene 93 2t 22
Benzo[a]anthracene 57 d: 7
Chrysene 63 :t 6
Benzo[b]fluoranthene & 89 i 6
Benzo[k]fluoranthene

Benzo[a]pyrene 60 :i: 8
Indeno[1,2,3-c,d]pyrene & 59 i 9
Dibenzo[a,h]anthracene

Benzo[ghi]perylene 55 i 4

 

 

59

Table 6.2

SFE Conditions used for the Extraction of Native PAHs from Soil C

 

 

 

Prepmaster Method
Pressure 300 atm
Temperature 90 °C

 

Extraction Time

1 minute Static

5 minutes Dynamic
5 minutes Dynamic
10 nrinutes Dynamic
10 minutes Dynamic

 

 

 

 

 

 

 

 

Extraction Vessel Size 3 ml

Accutrap Method

Collection Temperature -20 °C

Desorption Temperature 15 °C

Desorption Rinse 3 ml of methanol
at 1.0 ml/min

Flush Temperature 15 °C

Flush Rinse 5 ml of methanol
at 1.0 ml/min

Restrictor 150 °C

3.2 ml/min flowrate

60

Table 6.3

Percent Recovery of PAHs from Soil C with the SFE at 90 °C and 300 atm

       
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

_T,,,,;,If,z(,,,1n) ___________________

Naphthalene 125 i 33 177 i 36 194 :t 40 198 a: 42
Phenanthrene 88 at 18 1 13 i 22 126 i 22 130 i 22
Fluoranthene 52 d: 3 76 2t 6 94 :1: 6 101 i 5
Pyrene 54i6 80i8 102i8 110:7
Benzo[a]anthracene 20 at 5 28 i 10 42 2t 10 48 :t 1 1
Chrysene 18:2 27i6 43:6 52:5
Benzo[b]fluoranthene & 8 i l 13 d: 4 22 i 5 29 :t 6
Benzo[klfluoranthene

Benzo[a]pyrene 7 d: 3 13 i 2 20 2t 4 25 :1: 6
Indeno[1,2,3-c,d]pyrene & 2 i 1 3 :1: l 5 i 1 7 i 1
Dibenzo[a,h]anthracene

Benzo[ghi]perylene l :t l 2 :t 1 4 i 1 6 i 2

 

61

 

 

 

 

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62

100% of the Soxhlet values. The high standard deviation for naphthalene may be due to
its volatility. The high standard deviation for the phenanthrene may be due to baseline
noise in the region of the chromatogram were the peak elutes. F luoranthene and pyrene

were both extracted at 100% efficiency, but all other compounds had recoveries of <50%.

6.3 45 Minute Dynanmic Extration with SFE at 90 °C and 300 atm

The next set of extractions were performed using the same SFE conditions listed in
Table 6.2, except that the collection of the analyte was not fractionated. Instead, one 45
minute dynamic extraction replaced the fractionated dynamic steps. This was done for
two reasons: (1) fractionated collection of analytes makes the concentrations in the
samples low and this was a concern with regard to GC analysis, and (2) the longer
extraction time might increase recovery of the higher molecular weight PAHs. The results
of the extraction are shown in Table 6.4. The results of the 45 minute dynamic extraction
and the fractionated collection are compared graphically in Figure 6.2. It appears that the
GC analysis of the fractionated samples was accurate, as the 45 minute dynamic recoveries
were only slightly higher than the fractionated results. This was most likely the result of
the extra 15 nrinutes of dynamic extraction time, which allowed a larger volume of CO; to

be used as extractant for PAH recovery.

63

Table 6.4

Percent Recovery of PAHs from Soil C with the SFE at 90 °C and 300 atm

 

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Exam...» "
Tim: (mu!) £25}

 

Naphthalene

231:50

 

Phenanthrene

140:1:4

 

Fluoranthene

110:1:20

 

Pyrene

129i 12

 

Benzo[a]anthracene

60:5

 

Chrysene

61:1:5

 

Benzo[b]fluoranthene &
Benzo[k]fluoranthene

37:3

 

Benzo [a]pyrene

27i2

 

Indeno[1,2,3 -c,d]pyrene &
DibenzoLa,hlanthracene

llil

 

 

Benzo[ghi]perylene

 

9i1

 

64

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65

6.4 Fractionated Extraction using an Organic Modifier

The results of the fractionated extraction using methylene chloride as an organic
modifier with the SFE at 90 °C and 300 atm are shown in Table 6.5. The SFE conditions
were the same as those listed in Table 6.2. The Soil C sample was placed in the extraction
vessel and 700 pl of methylene chloride was added directly to the soil. The recoveries of
the higher molecular weight PAHs were increased compared to the recoveries obtained
without methylene chloride as a modifier. The rates of extraction are depicted in Figure

6.3.

6.5 45 Minute Dynanmic Extration using Organic Modifier

The results of the 45 minute dynamic extraction with methylene chloride as a
modifier and the SFE at 90 °C and 300 atm are shown in Table 6.6. SFE conditions were
the same as those listed in Table 6.2, with the exception of a 45 minute dynamic extraction
replacing the fractionated extraction steps. The results of the 45 minute dynamic
extraction and the fractionated collection are compared graphically in Figure 6.4. Also, a
graphical comparison of the 45 minute dynamic extraction with and without organic
modifier is shown in Figure 6.5. The modifier had the largest effect on the recovery of the

higher molecular weight PAHs.

66

Table 6.5

Percent Recovery of PAHs from Soil C using an Organic Modifier

igéCummulatix/e
§ggExtraction
Time (min)

1

 

 

Naphthalene

150i51

171i53

179:53

1793:54

 

Phenanthrene

129i 15

144i 14

1503: 13

150i l4

 

F luoranthene

761:9

862t10

93i9

96i9

 

Pyrene

901:12

102$ 12

112$”

116$”

 

Benzola]anthracene

Sli6

56i6

60i6

60i7

 

C hrysene

463:4

523:4

5913

65i3

 

Benzo[b]fluoranthene &
Benzo[k]fluoranthene

36i7

41i7

462t7

49i8

 

Benzo[a]pyrene

32i5

35i8

39i9

4li9

 

lndeno[ 1,2,3-c,d]pyrene &
DibenzoLa,hjanthracene

241:5

25i5

25i6

263:6

 

 

Benzo[ghi]perylene

 

l7i5

 

18i5

 

192t5

 

20d:5

 

67

 

 

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68

Table 6.6
Percent Recovery of PAHs from Soil C using an Organic Modifier

Tme (m) A

 

 

Naphthalene 202 :t 25

 

Phenanthrene 162 :t 2

 

Fluoranthene 109 :t 9

 

Pyrene 129 i 6

 

Benzo[alanthracene 68 i 4

 

Chrysene 71 i 4

 

Benzo[b]fluoranthene & 57 i 4
Benzo[k]fluoranthene

 

Benzo[a]pyrene 52 i 3

 

Indeno[1,2,3-c,d]pyrene & 33 i 4
Dibenzoghknthracene

 

 

 

 

Benzo[ghi]perylene 26 i 1

69

 

 

  
 
   
 
  

 

 

 

 

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Figure 6.4
PAH Concentrations Determined by Fractionated Collection and 45 Minute Dynamic

with 700 pl Methylene Chloride Modifier

70

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71
6.6 Fresh Spike Recovery using an Organic Modifier

The low recoveries of some of the PAHs could be a result of solubility limitations
of the PAHs in the supercritical fluid. To determine if solubility is a limiting factor a fresh
PAH spike was added to Soil C. The fresh PAH spike of 200 pl was added to the soil
sample in the extraction vessel and then 500 pl of methylene chloride was added as
organic modifier. The sample was extracted with the same SFE conditions as shown in
Table 6.2, with the exception that the dynamic extraction time was 45 minutes, instead of
the analyte collection being fractionated. The results are shown in Table 6.7. The
recoveries indicated that the solubility of the PAHs was not a factor affecting the efficient
extraction of PAHs.

The recoveries were calculated by subtracting the PAH concentrations determined
by SFE of the native PAHs from the concentrations of the spiked plus native PAHs in Soil
C. The SFE conditions were the same for the extraction of the native PAHs and for the
spiked plus native PAHs. The calculation was done for all PAH compounds that were
quantitated. Only four of the PAHs were in the fresh spike solution. The results show
that the concentration of the remaining native PAHs were within i 4 p g/ g for the two SFE

extractions performed (Table 6.8).

72

Table 6.7

Percent Recovery of Fresh Spiked PAHs from Soil C using an Organic Modifier

 

 

 

 

 

 

aficamaaaaaaaa '
EmaCti-Ofl . .
grime (mm) ‘ = 45
Naphthalene 80 i 11
Phenanthrene 1 13 i 21
Pyrene l 10 2t 21
Benzo[a]pyrene 81 2t 6
Table 6.8

Difference in Native PAH and Spiked plus Native PAH Concentrations

 

 

 

 

 

 

 

 

 

 

 

 

‘ wave—if ‘.iisaikadaNativaii Dace
jg} (pg/g. 'of’soil) ' 9;: (pg/g 05ml), 32‘?) (p g/gg: of soil) ‘ ‘ [

Naphthalene 22 d: 3 85 d: 10 63 i: ll
Phenanthrene 133i2 214:1:21 813:2]
Fluoranthene 82 3c 7 80 :l: 7 -3 :1: 9
Pyrene 119 i 5 203 d: 20 84 i 21
Benzo[a]anthracene 39 i 3 43 i 6 4 2t 7
Chrysene 45 d: 3 44 i 7 -l i 7
Benzo[b]fluoranthene & 50 i 3 51 i: 5 1 :t 6
Benzo[k]fluoranthene
Benzo[a]pyrene 3| i 2 89 i 6 58 i 6
Indeno[1,2,3-c,d]pyrene & 19 i 3 23 i l 3 i 3
Dibenzo[a,h]anthracene
Benzo[ghi]perylene 14 i 1 17 i l 3 i 1

 

 

 

 

73
6.7 Solvent Rinse of Cryogenic Trap

The other parameter that might have had an impact on extraction efficiencies was
the type of solvent used to rinse the cryogenic trap. Methanol had been used because it
was compatible with the delivery pump. Methylene chloride may be a better rinse solvent
for PAHs, because PAH solubility is higher in methylene chloride than in methanol. The
results of using methylene chloride and methanol as rinse solvents are shown in Table 6.9.
Extractions were performed using an organic modifier with the SFE conditions the same
as in Table 6.2, except a 45 minute dynamic extraction was used instead of fractionated
steps. A statistical analysis using the Student t test was performed with a 95% confidence
interval and there was no statistical difference in PAH recovery between the two rinse

solvents.

74

Table 6.9

Percent Recovery of PAHs from Soil C using an Organic Modifier
and Different Cryogenic Trap Rinse Solvents

e .

Exaracu anaemia) .,

 

Cwogeuc’l‘rap
a ' ' » -_..~ 32:44‘1i-9f-iflif 2;, 313335490“ .

..............................................................

 

Naphthalene

202 i 25

l74i31

 

Phenanthrene

162i2

154i10

 

Fluoranthene

109:1:9

llZilO

 

Pyrene

129i6

123i6

 

Benzo [a]anthracene

68i4

753:6

 

C hrysene

712t4

683:5

 

Benzo[b]fluoranthene &
Benzo[klfluoranthene

57i4

53i4

 

Benzo[a]pyrene

52i3

522t5

 

Indeno[1,2,3-c,d]pyrene &
Dibenzo [a,h1anthracene

33i4

3l:t7

 

 

Benzo[ghi]perylene

 

263:1

 

282t6

 

 

75

6.8 Aged Spike Recovery using an Organic Modifier

The fresh PAH spike extraction from Soil C indicated that solubility was not a
limiting factor affecting the SFE efficiency for the PAHs. The extraction process could
instead be limited by the diffusion of the analytes from the matrix. The aged PAH spiked
Soil C was used to show any indications that diffusion limitations may possibly be the
cause of the low recoveries of the native PAHs. The extractions were performed using
both SFE and Soxhlet extraction techniques. The SFE conditions were the same as those
listed in Table 6.2, with the exception that the dynamic extraction time was 45 minutes
and the sample collection was not fractionated. The results were compared to the
theoretical PAH concentrations determined from the amount of PAHs spiked onto the soil
(Figure 6.6). The results were obtained by subtracting the native PAH concentrations
from the native plus aged spike concentrations, as determined by both SFE and Soxhlet
extraction (Table 6.10). The results indicate that diffusion may be a limiting factor for the
SFE conditions used as the ring size and molecular weight of the PAHs increase. The
Soxhlet extraction results show less of a dependence on ring size and molecular weight,
but the Soxhlet extraction has a higher deviation in the triplicate samples extracted than

the SFE.

76

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77

Table 6.10

Difference in Native PAH and Spiked plus Native PAH Concentrations as
Determined by SFE and Soxhlet Extraction

SFE : ' SoxhletExtractron

V "   : if .2 ’ I rag/aaraam i ‘ i. x ‘ (pg/gofsofl) i

 

Naphthalene

4li6

113:10

 

Phenanthrene

253$ 12

121i82

 

Fluoranthene

Zill

-4:t29

 

Pyrene

132i l6

96i79

 

Benzo[a]anthracene

-li5

-12i 18

 

Chrysene

-3:l:4

-11i20

 

Benzo[b]fluoranthene &
Benzo[k]fluoranthene

-7i9

-ll:l:18

 

Benzo [a]pyrene

57:1:17

128d: 54

 

Indeno[1,2,3-c,d]pyrene &
Dibenzo [a, h] anthracene

ai4

-7:tl4

 

 

Benzo[ghi]perylene

 

-2:l:3

-10:l: 12

 

 

78

6.9 Fractionated Extraction using an Organic Modifier and 150 °C

The indication that diffusion may possibly be a limiting factor for the extraction of
the native PAHs led to the decision to increase the extraction temperature. Increasing the
extraction temperature could be beneficial for a system that is limited by diffusion. The
higher temperature could provide the energy necessary to overcome the diffusion energy
barrier that may exist. TheSFE conditions were the same as those listed in Table 6.2, with
the exception of the temperature being 150 °C instead of 90 °C. The results of the
fractionated collection are shown in Table 6.5 and Figure 6.7 and are based on the PAH
concentrations obtained from the Soxhlet extraction of Soil C. The increase in the
extraction temperature did not satisfactorily increase the recovery of the native PAHs from

Soil C compared to the results obtained at 90 °C.

79

Table 6.11

Percent Recovery of PAHs from Soil C using an Organic Modifier

and Temperature of 150 °C

Cummulatlve ” ' "

Tune (mm) _

 

 

Naphthalene

144117

207:1: 15

230i 17

234i17

 

Phenanthrene

122i20

146i7

153i7

153i7

 

Fluoranthene

69118

83i10

93i7

953:6

 

Pyrene

79il7

97i9

111i5

115i5

 

Benzo[g] anthracene

49il3

56ilO

63i8

66:1:8

 

Chrysene

4421212

533:8

64i7

69i4

 

Benzo[b]fluoranthene &
Benzo[k]fluoranthene

37ill

42:1:8

49i8

53i7

 

Benzo[a]pyrene

36i9

40i7

453:6

47i5

 

Indeno[1,2,3-c,d]pyrene &
Dibenzo[a,h]anthracene

242t6

25:1:5

26i5

263:5

 

 

Benzo[ghi]perylene

 

21i7

 

22:1:6

 

24i6

 

253:6

 

80

 

 

 

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81

6.10 C02 and Modifier Contact Time

The addition of methylene chloride modifier had a large effect on the recovery of
native PAHs from Soil C. The largest difference in recovery was noticed in the first five
minutes of the extraction process. The methylene chloride added to the extraction cell
was most likely flushed from the cell during the first 5 minute dynamic extraction. The
contact time of the methylene chloride was changed by changing the static extraction time
prior to the dynamic extraction to try to increase the recovery of the native PAHs. The
results of changing the static and dynamic extraction times are shown in Figure 6.8 and
Figure 6.9. There was a statistically significant increase in the recovery of phenanthrene,
fluoranthene, pyrene, benzo[a]anthracene, chrysene, benzo[b]fluoranthene, and
benzo[k]fluoranthene when the static extraction time was increased from 1 minute to 5
minutes with a 5 minute dynamic extraction time. Again, the Student t test with a 95%
confidence interval was used to test the data. There was no a statistically significant
increase in the recovery of the PAHs over that obtained by the 5 minute static/5 minute
dynamic'when the dynamic extraction time was increased to 10 minutes.

The addition of methylene chloride to the 5 minute static/5 minute dynamic
extraction was then compared to the 45 minute dynamic extractions with and without
methylene chloride added (Figure 6.10). As the molecular weight of the PAHs increases,
there was a larger affect noticed from the addition of methylene chloride modifier. The 5
minute static/5 minute dynamic extraction with methylene chloride modifier showed a

statistically significant increase in the recovery of benzo[a]pyrene, indeno[1,2,3-c,d]pyrene

82

& dibenzo[a,h]anthracene, and benzo[ghi]perylene when. compared to the recovery
obtained using a 1 minute static/45 minute dynamic without methylene chloride modifier
added to the extraction cell. When compared to the 1 minute static/45 minute dynamic
with methylene chloride modifier added, the 5 minute static/5 minute dynamic had
statistically lower recoveries for all the PAHs except naphthalene and indeno[1,2,3-

c,d]pyrene & dibenzo[a,h]anthracene.

83

 

 

 

 

 

I5 min Static/5 min Dynamic

'.‘u

1 min Static/5 min Dynamic

 

 

 

 

 

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....................................

 

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120

 

 

 

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Figure 6.8
Concentration of PAHs Recovered from Soil C with Change in Static Extraction Time

84

 

 

 

 

 

 

 

 

 

 

 

  
 
 

 

 

 

 

    

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Figure 6.9
Concentration of PAHs Recovered from Soil C with Change

in Static and Dynamic Extraction Time

85

 

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Concentration of PAHs Recovered from Soil C after Different Extraction Times

CHAPTER 7

CONCLUSIONS AND RECOMMENDATIONS

7.1 Conclusions
Ottawa Sand was used as an inert material from which PAHs could be

extracted using SFE with C02 modified with 1% methylene chloride. Initially, extractions
were done to determine the reproducibility of the SFE extraction efficiencies. Recoveries
were initially low, but various changes were made to the SFE apparatus that increased the
PAH recovery from the Ottawa Sand. The changes made to the SFE included fixing the
nitrogen purge line, changing a plugged vent line, lowering the cryogenic trap desorption
temperature, and using methanol instead of methylene chloride as a rinse solvent. A
variety of temperature and pressure combinations were then tested to determine the effect
on PAH extraction from the Ottawa Sand. The only effect noticed was the increase in
benzo[a]pyrene recovery when the pressure was increased from 200 atm to either 300 atm
or 400 atm. The recoveries for all four compounds were >85% at all temperatures and
pressures tested, except when 200 atm pressure was used.

The extraction of the freshly spiked PAHs proved to be a little more difficult when
the matrix was changed from Ottawa Sand to Soil A. Naphthalene, phenanthrene, and
pyrene were all extracted with recoveries > 85% at 90 °C and 300 atm, but

benzo[a]pyrene had a recovery of only 66%. Increasing the temperature did not increase

86

87

the benzo[a]pyrene recovery. The addition of methylene chloride as an organic modifier
did increase the recovery of benzo[a]pyrene, with the temperature at 90 °C and pressure at
300 atm. The recovery of the PAHs from Soil A that had aged for over a year was
affected by both the organic modifier and temperature. The addition of methylene
chloride as an organic modifier increased the recovery of benzo[a]pyrene from 49% to
77%. Increasing the extraction temperature from 90 °C to 150 °C and adding methylene
choride increased the benzo[a]pyrene recovery from 49% to 93%.

The native PAHs in Soil C proved to be much more difficult to extract than the
freshly or aged spiked PAHs in Soil A. The SFE recoveries were compared to the Soxhlet
extraction recoveries. Not only was the overall recovery of PAHs increased when
methylene chloride was added as an organic modifier, but the rate of extraction was also
increased. In the first ten minutes of extraction with an organic modifier, all of the
recoveries were at or above the recoveries obtained after 30 minutes of extraction without

methylene chloride being added to the extraction vessel.

7.2 Recommendations

The development of a SFE method for PAHs in soils will be dependent upon the
matrix from which the PAHs are extracted. The difficult part of applying SFE as an
analytical tool is determining how the variables will effect the extraction performance. In
many cases known concentrations of analytes are spiked onto the matrix and extracted to
determine recovery efficiencies. This method can give a false recovery efficiencies, which

will be higher in most cases than the recovery efficiencies of the native PAHs.

88

Future work could include trying to determine a method by which extraction
efficiencies could be determined. This might consist of obtaining a variety of soil samples
from contaminated sites and performing SFE analysis to determine contaminant
concentrations. A database of information about the mechanical characteristics of the soil,
the age of the contamination, the SFE variables, and other conditions that affect the
recovery of analytes from the soil would be useful. This database could be accessed when
a SFE method is needed to analyze a contaminated soil sample. It would serve as a
starting point for the method development and also provide an indication of what type of
recoveries should be expected. Comparison to other extraction methods, such as soxhlet
or sonication, would also be a helpfiil addition to this database.

Although comparing SF E to conventional extraction methods can be beneficial,
one of the reasons for using SFE is to eliminate the use of conventional methods that
produce large amounts of organic waste. The SFE results could be compared to toxicity
information instead of being compared to conventional extraction methods. The basis of
cleaning up contaminated soils is that there is a hazard due to the toxic effects of the
pollutants present. If a link between SFE extraction recoveries and toxicity data could be
developed it would prove to be a helpful database of information.

Finally, there could be more work done to determine the effect of modifiers on the
extraction efficiencies obtained with SFE. There was a large affect seen in this research
when methylene chloride modifier was added to the extraction cell. The financial
limitations made it impractical to order more than one concentration of methylene chloride

mixed into the tank of SFE C02. It would be interesting to see how the increase in

89

methylene chloride concentration in the SFE C02 tank would affect the recovery
efficiencies by having a continual supply of the modifier at a higher concentration. The
type of modifier that is used for the extraction could be investigated as well. The modifier
seemed to play the most important role for increasing the extraction efficiencies of the

soils tested in this research.

APPENDICES

APPENDIX A

APPENDIX A

PHYSICAL CHARACTERISTICS AND STRUCTURES OF PAHS

‘ commune

Table A

Physical Characteristics and Structures of PAHs

' Emma-at

Formula

Weight; :- 2 F .

‘Moiaaurar

‘ (ig/maIr-l

. i Pointéi_ -

. __ Point-E13535: .

(C) I _

Structure

.......

 

 

Naphthalene

CIOHS

128.16

80.2

217.9

 

Acenaphthylene

C12Hs

152.20

92-93

265-275

 

Acenaphthene

CI2H10

154.21

95

279

 

 

Fluorene

 

C13H10

166.21

 

 

116-117

295

 

 

 

90

 

 

91

Table A (cont’d)

 

 

 

 

 

 

 

 

 

Phenanthrene C ”Hm 178.22 100 340

Anthracene CHHIO 178.22 218 342

Fluoranthene Cmfllo 202.26 NA 375 ©'©

O

Pyrene C15H10 202.24 156 404 ©©©©

Benzla]anthracene ClsHu 228.28 162 435 O
©©©

Chrysene Clan 228.28 254 448 O

 

 

 

 

 

 

 

j . Compound: ‘ ,

92

Table A (cont’d)

' :igEm-piriical ‘
“mm .

Moi. '

melting
_ . Pom-8.1.9.23
1if?}?li¥‘;(°C)Fiii???

113991118 :

' . Structure

Pomt
Eil(°C) -f:ji;;s§?;:.j; g. ' : -. ;_ ;:

 

Benzo[b]fluoranthene

CZOH 12

252.32

163-165

NA

%
.Q
Q

 

Benzo[k]fluoranthene

C20H12

252.32

215-217

NA

0
e
<98

 

Benzo[a]pyrene

C20H 12

252.30

l79-179.3

310-312

 

Indeno[123-cdlpyrene

C22H12

276.34

NA

NA

E58

 

Dibenzlahlanthracene

C22Hl4

278.35

266-267

524

90
©
96

 

 

Benzo[ghi]perylene

C2231:

 

 

276.34

 

277-279

>500

 

 

 

 

APPENDIX B

APPENDIX B

SOXHLET EXTRACTION PROCEDURE FOR PAH CONTAMINATED SOIL

I. Extraction
II. Clean-up
III. Concentration

I. Extraction Procedure for PAH Contaminated Soil

Extraction

1. Pour 300 ml of methylene chloride (MeClz) into the round bottom flask.

2. Add a few boiling chips to the flask.

3. Place the thimble containing the soil sample in the soxhlet extractor and connect
glassware.

4. Turn heating blocks on high and turn cold water on to the condenser.

5. Extract samples about 24 hours.

Solvent Exchange

1.

After the extraction is complete, remove the thimble from the soxhlet extractor and
discard the Mer contained in the thimble holder. Allow the MeClz containing the
analyte in the round bottom flask to cool before disconnecting the thimble holder.
Squirt methanol on the outside of the glassware in order to assist the cooling
process of the vapors in the round bottom.

Distill the remaining Mer in the round bottom flask until there is approximately
100 ml left. Avoid concentrating the liquid to a level where solids form or attach
to the walls of the flask.

Remove the unit (cooling the glassware again before disconnecting any joints) and
add 200 ml of cyclohexane to the flask. Distill off the rest of the MeClz.

Remove the unit (cool the glassware) and place a ground glass stopper on the
flask.

The Clean-up Procedure can be started.

93

II.

III.

94

Clean-up Procedures for PAH Extraction Samples
**Before starting this procedure, turn the water bath on**

Pour the cyclohexane containing the analyte from the round bottom flask into the
drying tube (2 cm x 20 cm) containing 30 g of freshly activated silica gel and 15 g
of sodium sulfate. The sodium sulfate is placed on top so that the cyclohexane
comes in contact with it before reaching the silica gel. Use glass wool to plug the
bottom of the drying tube.

Rinse the silica gel column with pentane, approximately 60 ml. The last few drops
of pentane should be clear, if not, then add more pentane until the eluate is clear.
Rinse the silica gel with 60% pentane/40% MeClz (v/v) to remove the PAHs.
Collect the liquid in a clean flask. Use 200 ml of the 60/40 mixture to rinse the
PAHs from the silica gel.

Take the flask containing the PAHs in the 60/40 mixture of pentane and Mer and
proceed with the concentration operation.

Concentration Operation for PAH Extraction Samples

Assemble the concentrator tube and the boiling flask using a teflon sleeve at the
ground glass joint.

Pour the sample into the boiling flask and add a small boiling chip. Rinse the
sample flask out with Mer and pour into the boiling flask.

Attach the Snyder column, pour 10 ml of Mer down the snyder column, and
mount the assembly above the water bath clamping onto the neck of the flask.
Lower the assembly into the water bath and secure with clamps.

Once the evaporation/concentration is complete (to a few mls), remove the
assembly and wipe off the excess water at the base of the flask and around the
concentrator tube.

Squirt methanol on the glassware to assist in cooling and then remove the Snyder
column and add 1 or 2 ml of Mer to the flask and spin. This should rinse down
the sides of the flask.

Rinse the joint between the flask and tube with MeClz and then remove the flask.
Be sure to remove the teflon sleeve also.

Add MeClz to the sample to obtain the desired volume. For most purposes the
total volume will usually be 6 ml or 10 ml, note the volume used.

Fill two or three GC vials with the sample and discard the rest into the waste
bottle. Store the GC vials in the freezer until they can be analyzed on the GC.

APPENDIX C

APPENDIX C

COST COMPARISON OF SFE AND SOXHLET EXTRACTION IVIETHODS

The costs for consumable items of both the SFE and Soxhlet extraction methods
are listed in Table B and Table C. Included in the costs are only those items which are
non-reusable. For instance, neither extraction method has the cost of glassware included
in the cost analysis. Also, labor costs and waste disposal cost have not been included.
The cost of the Soxhlet extraction would increase significantly more than the SFE method
if waste disposal were included.

The SFE cost is a conservative number and may be actually lower for most
samples. This is due to assumptions made about the amount of SFE C02 used per sample,
the number of frits used per sample, and the number of restrictors used per sample. The
two most expensive items for the SFE analysis are the restrictors and SFE C02. The
assumption made was that the dynamic extraction time would be 45 minutes with a flow
rate of 2.2 ml/min. This is highly dependent on the type of matrix and analyte of interest.
The number of samples that can be processed using the same restrictor is also dependent
on the sample type. The restrictors need to be replaced if and when they become plugged.
There may or may not be waxes and other materials within the sample that can plug the
restrictor.

95

96
Table B

Soxhlet Extraction Consumables Cost

 

7 QFCOStPerg$fimpla

» «tag.

 

 

Extraction Thimble,
Cellulose, 43 x 123,
1.5 mm wall thickness 5.?-

$60.00/box of 25
thimbles

1 thimble

$2.40

 

Methylene Chloride,
99.9%, HPLC Grade ‘1

$155.00/l6 L

380 ml

$3.68

 

Pentane, 99.9%,
Capillary GC Grade ‘I’

$266.15/16 L

200 ml

$5.32

 

Cyclohexane, 99.9%,
HPLC Grade 1‘

$120.80/8 L

200 ml

$3.02

 

Sodium Sulfate, 99+%,
granular, ACS reagent ‘1’

$16.35/500 g

15g

$0.50

 

Silica Gel, 99+%,
Davidsil grade 644,

$110.50/kg

$3.32

 

 

100-200 mesh 1*

Total Cost   I .. >

”MNWUb .

 

L51 Supelco, Bellefonte,PA, USA M H
‘1’

Aldrich, Milwaukee, WI, USA

 

 

 

 

9 7
Table C

SFE Consumables Cost

Maternal 57:55?Priceii?fixifiiir. * " AmwntUsed 1] CostperSample
;. ..:-:‘-:':Iii-52']? i5; . . 53:1 ‘:i_?§;i:i.?!i'_'f:: i per Sample iii-iii .féégiiéfig};

 

Septa, heavy duty, $19.80/pack of 100 1 septa $0.20
0.01” PTFE bonded
over 0.09” silicone 1’

 

Restrictors, $3 54.60/pack of 6 1/25 samples $2.36
Stainless Steel 53

 

Extraction Cell Frits 3 $80.10/pack of 12 1/25 samples $0.27

 

SFE C02 w/ 1% Mer $494.00/ 17.69 kg 70 g $1.95
Helium Headspace ii

 

Bone Dry C02, 99.8% i? $35.00/27.22 kg 270 g $0.35

 

Nitrogen, 99.99%, $36.00/Cylinder Size K 1 tank/200 $0.18
High Purity ii samples

 

Methanol, 99.9+%, $109.20/16 L 8 ml $0.06

 

 

-ACSHPLC Grade _‘ .. .

 

 

 

TotalCost ‘ “man-«$530

"7’ Fisher Scientific, Pittsburgh, PA, USA

if. Suprex, Pittsburgh, PA, USA

i? Scott Specialty Gases, Plumsteadville, PA, USA
"‘ Aldrich, Milwaukee, WI, USA

 

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