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. . thesis entitled .
Three D1men31onal Fluorescence And Capillary

Gas Chromatography Of Neat And Evaporated
Gasoline Samples

presented by
Laureen J. Marinetti-Sheff

has been accepted towards fulfillment
of the requirements for

 

Master Of Science degree in Criminal Justice

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THREE DIMENSIONAL FLUORESCENCE AND CAPILLARY GAS
CHROMATOGRAPHY OF NEAT AND EVAPORATED GASOLINE
SAMPLES
by

Laureen Marinetti-Sheff

A THESIS

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

MASTER OF SCIENCE
College of Social Science
School Of Criminal Justice

1990

647 _ (.2341 0- (.3

Abstract
Three Dimensional Fluorescence Spectroscopy and

Capillary Gas Chromatography 0f Neat And Evaporated
Gasoline Samples

by

Laureen Marinetti-Sheff

Arson is an expensive and dangerous crime in the
United States today. Prosecution of this offense depends
on locating and placing a suspect at the scene. Most of
the physical evidence is destroyed by the fire but usually
the accelerant used can be successfully recovered. The
common method of analysis of accelerants is capillary gas
chromatography.

Capillary gas chromatography and three dimensional
fluorescence spectroscopy were used to analyze nine
assorted brands and grades of gasolines both neat, 50% and
100% evaporated. Capillary gas chromatography could not
distinguish between any of the samples either neat or
evaporated nor could it relate an evaporated sample back to
its unevaporated form.

Three. dimensional fluorescence spectroscopy can
distinguish the samples neat and evaporatedt It could not
relate a totally evaporated gasoline sample back to either
the original neat one or the 50% evaporated one. The
comparisons were made both visually and with a subtraction

program.

ACKNOWLEDGEMENT

First and foremost I would like to thank my husband,
Bernard, who always gave his support and instilled in me
the confidence I needed to complete this thesis. II would
also like to thank my co-workers at the Michigan State
Police Crime Lab in East Lansing for their support and
help.

In addition I would like to send a special thanks to
my parents who greatly simplified this work by providing
personal computer and to my inlaws who happily babysat my
son, Benjamin, while I completed this work.

In conclusion I would like to thank Dr. Jay Siegel for
his help in getting me "up to snuff" in an area that I had
not worked in for a long time. Without his help it would

have been impossible for me to finish this thesis.

Table f QQQE§£E§

 

List Of Tables 0 O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 0 iii
List Of Figures 0 O O O O O O O O O O O O O O I O O O O O O O O O O O O O O O O O O O O O O O O O 0 iv
Chapter 1 - Introduction................................. 1

Chapterz Literature ReVieWOOOOOOOOOOOOOOO0.00.0.0...O. 7

Materials And Methods........ ......... .......18

Chapter 3

Chapter 4 Results......................................21

Discussion And Conclusion....................83

Chapter 5

References. .............. . .......... . ................. ...91

ii

List 9; Tables

 

The excitation and emission wavelengths at maximum
intensity of the neat gasoline samples..............22

The excitation and emission wavelengths at maximum
intensity of the 50% evaporated gasoline samples....23

The excitation and emission wavelengths at maximum
intensity of the 100% evaporated gasoline samples...24

iii

List 9; Eiggres

 

An example of an emission scout spectrum...........25
An example of an excitation scout spectrum... ...... 26

Capillary gas chromatogram of Mobil Unleaded
gasoline neat...... ........ ......... ..... . ......... 27

Capillary gas chromatogram of Mobil Super
Unleaded gasoline neat............. ...... . ......... 28

Capillary gas chromatogram of Shell Regular
gasoline neat ..... .. ..... .......... ......... . ...... 29

Capillary gas chromatogram of Shell Unleaded
gasoline neat..................... ...... ...........30

Capillary gas chromatogram of Standard
Regular gasoline neat.. ................... ....... .31

Capillary gas chromatogram of Standard
Unleaded gasoline neat............. ....... .... ..... 32

Capillary gas chromatogram of Standard
Premium gasoline neat......... ..................... 33

Capillary gas chromatogram of Total Regular
gaSOIine neat....OOOOOOO0.0.0.0.... ...... O... ...... 34

Capillary gas chromatogram of Total Unleaded
gaSOJ-ine neat.....OO ........ 00...... ..... COO-OOOOOO35

Capillary gas chromatogram of Mobil Unleaded
gasoline 50% evaporated..................... ....... 36

Capillary gas chromatogram of Mobil Super
Unleaded gasoline 50% evaporated.. ...... . .......... 37

Capillary gas chromatogram of Shell Regular
gaSOJ-ine 50% evaporatedOOOOOOOOO00.000.000.000...0.38

Capillary gas chromatogram of Shell Unleaded
gasoline 50% evaporated.............. ..... .........39

Capillary gas chromatogram of Standard Regular
gaSOIine 50% evaporatedOOOOOOOOOO0.000000000000000.40

iv

Capillary gas chromatogram of Standard Unleaded
gasoline 50% evaporated............................41

Capillary gas chromatogram of Standard Premium
gaSOIine 50% evaporated.....OOOOOOI...00.0.0000000042

Capillary gas chromatogram of Total Regular
gasoline 50% evaporated....................... ..... 43

Capillary gas chromatogram of Total Unleaded
gasoline 50% evaporated............................44

Capillary gas chromatogram of Mobil Unleaded
gaSOJ-ine 100% evaporated....OO0.00.00.00.000 ....... 45

Capillary gas chromatogram of Mobil Super
Unleaded gasoline 100% evaporated............ ...... 46

chromatogram of Standard Regular
evaporatedOOOOOOO...0.0.0.0...IO..00047

Capillary gas
gasoline 100%

chromatogram of Standard Unleaded
evaporatedOOOOOOOOOIOOO0.0.0.0000000048

Capillary gas
gasoline 100%

chromatogram of Standard Premium
evaporated..OOOOOOOOOOOOOO0.0...O...049

Capillary gas
gasoline 100%

chromatogram of Total Regular
evaporated.....OOOO0.00.0.0.0... 00000 50

Capillary gas
gasoline 100%

chromatogram of Total Unleaded
evaporated....OOOOOOOOIOOOOOOOOOOOO0.51

Capillary gas
gasoline 100%

Three dimensional fluorescence stacked emission
plot of Mobil Unleaded gasoline neat...............52

Three dimensional fluorescence stacked emission
plot of Mobil Super Unleaded gasoline neat.........53

Three dimensional fluorescence stacked emission
plot of Shell Regular gasoline neat................54
Three dimensional fluorescence stacked emission

plot of Shell Unleaded gasoline neat...............55

Three dimensional fluorescence stacked emission
plot of Standard Regular gasoline neat.............56

Three dimensional fluorescence stacked emission
plot of Standard Unleaded gasoline neat............57

Three dimensional fluorescence stacked emission
plot of Standard Premium gasoline neat.............58

Three dimensional fluorescence stacked emission
plot of Total Regular gasoline neat................59

Three dimensional fluorescence stacked emission
plot of Total Unleaded gasoline neat...............60

Three dimensional fluorescence stacked emission
plot of Mobil Unleaded gasoline 50% evaporated.....61

Three dimensional fluorescence stacked emission
plot of Mobil Super Unleaded gasoline 50%
evaporated..00.0.0.0...OIOOOOOOOOOOOOOOOOOOOOOO0.0.62

Three dimensional fluorescence stacked emission
plot of Shell Regular gasoline 50% evaporated......63

Three dimensional fluorescence stacked emission
plot of Shell Unleaded gasoline 50%
evaporated.....OOOOOOOOOOOOOOOOOOOOO0.0.0.... ...... 64

Three dimensional fluorescence stacked emission
plot of Standard Regular gasoline 50%
evaporated.................................... ..... 65

Three dimensional fluorescence stacked emission
plot of Standard Unleaded gasoline 50%
evaporated..OOIOOIOOOOOOOOOOOO 000000000000 O... ..... 66

Three dimensional fluorescence stacked emission
plot of Standard Premium gasoline 50%
evaporated.. ............... .... .......... ..........67

Three dimensional fluorescence stacked emission
plot of Total Regular gasoline 50% evaporated......68

Three dimensional fluorescence stacked emission
plot of Total Unleaded gasoline 50% evaporated.....69

Three dimensional fluorescence stacked emission
plot of Mobil Unleaded gasoline 100% evaporated....70

Three dimensional fluorescence stacked emission
plot of Shell Unleaded gasoline 100% evaporated....71

Three dimensional fluorescence stacked emission

plot of Standard Unleaded gasoline 100%
evaporated................................. ........ 72

vi

Three dimensional fluorescence stacked emission
plot of Standard Premium gasoline 100%
evaporated.....OOO ...... OIOOOOOOOOOOOOOOOOOOOO ..... 73

Three dimensional fluorescence stacked emission
plot of Total Unleaded gasoline 100% evaporated....74

The resultant subtraction plot of Standard
Premium neat minus Standard Unleaded neat... ....... 75

The resultant subtraction plot of Standard
Premium 50% evaporated minus Standard Unleaded
50% evaporated...OOOOOOOOOOOOOOOOOO0.00.00.00.00..076

The resultant subtraction plot of Standard
Unleaded 100% evaporated minus Standard Premium
100% evaporated.....OOOIOOOIOOOOOOOOOOOOOOOOOOOOOOO77

The resultant subtraction plot of Total Regular
neat minus Shell Regular neat......................78

The resultant subtraction plot of Mobil
Unleaded neat minus Shell Unleaded neat............79

The resultant subtraction plot of Total
Unleaded neat minus Shell Regular neat.............80

The resultant subtraction plot of Mobil Super
Unleaded 50% evaporated minus Mobil Super
unleaded neat....OOOO0.000000000000000.0.000000000081

The resultant subtraction plot of Total Unleaded

100% evaporated minus Standard Unleaded 100%
evaporated.....OOOOO ........ OOOOOOOOOOOOOOOOOOOO00.82

vii

Chapter One
Introduction

Arson is a very serious crime in the United States
today. It costs Americans billions of dollars each year in
damages, not to mention thousands of deaths and injuries.
Despite the fact that arson is so widespread, arrests of
the perpetrators of these crimes are alarmingly low. Out
of 5,497 arson crimes in Michigan in 1987 only 8.9% were
cleared by arrests(1). This is due to the nature of arson
itself.

Arson involves the malicious destruction of property
or material goods by intentionally setting it on fire.
This usually involves the rdeposit of some type of
accelerant to start and maintain the fire. The accelerant
is placed on, in or around the area or item to be burned.
It is then ignited by the perpetrator who usually leaves
the scene long before the fire is discovered. Any of the
usual types of evidence left at a crime scene such as
fingerprints, footprints" hair, fibers or blood. may be
either destroyed by the fire or by its extinguishing.

Thus in the ensuing investigation, it can usually. be
determined that a fire is arson but finding and convicting

the perpetrator depends on either an eye witness or someone

2
with knowledge of a person or persons who would have
something substantial to gain by setting the fire. If a
suspect is located, then the investigator must place him at
the scene. With most of the usual evidence destroyed this
can be a very difficult task.

If the fire was set using a liquid accelerant then
there is a good chance that some of it can be recovered.
Except in the case of gases or alcohols, rarely does a fire
consume 100% of the accelerant. Since the accelerant is a
liquid, it will usually soak into any porous material or
surface on which it is deposited. The portion of the
accelerant that soaks down into a porous surface, where
there is little or no oxygen present, will not be consumed
in the fire. In addition, even though thousands of gallons
of water may be used to put out the fire, a hydrocarbon
liquid accelerant will remain since it does not mix with
water. For example, gasoline or oil floats on the surface
of water.

Taking these facts into consideration and also that a
fire scene investigator can determine the origin of a fire
hence the prime location of an accelerant if it is present,
the investigator knows where to collect evidence. This
requires that any porous material present at and around the
fire’ s origin be collected in an air tight container and
sent to the forensic science laboratory as soon as

possible. If an accelerant is found in the possesion of a

3
suspect and this can be compared to the accelerant found at
the scene then, based on the results of the comparison, the
suspect may either be ruled out or the case against him
strengthened.

Hydrocarbon accelerants are inexpensive and readily
available. They can be purchased without raising any
suspicion. For instance it is extremely common to buy or
posses gasoline, lighter fluid or fuel oil, hence the
importance of hydrocarbon analysis by the forensic science
laboratory.

Currently, analytical methods used for hydrocarbon
analysis can differentiate among classes of petroleum based
products such as oils from gasolines or lighter fluids.
However, problems may arise when samples within the same
class of petroleum based products require differentiation,
such as two brands of gasolines.

This thesis addresses the problem of differentiation
among gasoline samples. Most forensic science laboratories
currently employ capillary gas chromatography to
characterize gasoline samples. However, chromatography is
inadequate for determining the specific brand or grade of
gasoline because the data is not discriminating enough.
Therefore a technique that will provide the necessary data
would be extremely valuable not only in the analysis of
gasolines but other petroleum products as well. Three

dimensional fluorescence has been evaluated as a possible

4

analytical technique in helping to provide more information
when analyzing gasolines and other hydrocarbons.

Fluorescence is a physical property that some
compounds have such that they can be excited to a higher
energy level and emit energy when they return to their
original energy level. When the compound is exposed to a
certain wavelength of light one of its electrons will be
energized to a higher energy level than its normal ground
state. However, the compound is not stable in this higher
energy state so the electron returns to the original ground
state. When this occurs a different wavelength of light
energy is given off than the original wavelegth. The
wavelength required to elevate to a higher energy level is
termed the excitation wavelength and the wavelength emitted
when the orignal ground state is acheived is termed
emission. Both the excitaiton and emission constitute
fluorescence. In two dimensional fluorescence
spectroscopy, a simple spectrum is derived by either
scanning the emission wavelength region while holding the
excitation wavelength constant or vice versa. However, in
three dimensional fluorescence a more complete picture of
the fluorescence characteristics of a sample is possible.
This is because a series of emission spectra are scanned
over the entire wavelength range of fluorescence while the
excitation wavelength is varied by a fixed increment. Each

of these spectra are then plotted in a pseudo three

5
dimensional array on the same set of axes. The x-axis
represents the emission wavelength, the y-axis represents
the excitation wavelength and the z-axis represents the
fluorescence intensity.

This thesis will build upon previous work done in this
area. It includes the analysis of nine brands and grades
of gasoline. They will initially be compared on the basis
of their three dimensional fluorescence plots to determine
if they can be differentiated by this criterion. A plot
subtraction program will be employed when necessary to
compare samples. This program subtracts one three
dimensional emission stack plot from another and calculates
a Pearson’s Q coefficient to determine the similarity of
the two plots. The closer Pearson’s Q is to one the more
similar the plots are. Capillary gas chromatograms will
also be obtained for the nine samples. Then the gasolines
will be evaporated under controlled conditions to observe
the effects of weathering on the fluorescence and the
chromatograms.

Evaporation will serve to more closely simulate the
actual conditions upon which gasolines are encountered in
forensic science case work. The evaporation will take
place in two steps. First each gasoline will be evaporated
to 50% of original volume and finally to dryness. Gas
chromatograms will also be obtained. The information

generated from the three dimensional fluorescence will be

6
analyzed to determine if gasoline samples are unique when

characterized by these methods.

Chants: 11:22
Literature REA—V'ew

EARLY CHROMATOGRAPHIC METHODS OF HYDROCARBON ANALYSIS

In the 1960's analysis of gasolines was primarily
concerned with characterization of the hydrocarbon
component. In an early article by Lucas (2) it was
demonstrated how different types of petroleum distillates
could be differentiated by gas chromatography. It was
shown how gasolines could be distinguished from kerosenes,
fuel oils, floor cleaners or varsol. Twenty eight
gasolines were studied. All of the samples separated into
26 fractions with 75% of the hydrocarbons in the 0-5 minute
retention time range. Point by point comparisons were
carried out and it was concluded that gas chromatography
had great potential in the identification of petroleum
products and the possibility of differentiation of brands
within a specific type.

A later study by Sanders et.al.(3) introduced a
capillary gas chromatography method that showed detailed
compositional data of hydrocarbons in complex gasoline
mixtures. They identified many of the 240 peaks that were
generated in the two hour run. They also noted a "light
end loss" (loss of low boiling point hydrocarbons) from the
front end of the chromatograms if the gasoline samples were
not kept refrigerated.

Subsequently gas chromatography and infrared

8
spectrometry were used by Ettling (4) for isolation and
identification of trace amounts of hydrocarbons in fire
remains. He determined that as little as 10mg could be
detected with infrared spectrometry. He used gas
chromatography as a backup method for further
characterization of the hydrocarbons.

Then Ettling et.al. (5) attempted to determine the
presence of an accelerant in fire remains by first devising
what a "normal level" of hydrocarbons in fire remains
would be. This was accomplished by first using headspace
gas chromatography followed by extraction of the remains
and liquid chromatography performed on the extract. The
authors decided that this method was not useful because
hydrocarbons could either be destroyed or created by the
combustion process of the fire thus making a "normal level"

of hydrocarbons an unmeasurable variable.

DEVELOPMENT OF OTHER METHODS OF ANALYSIS FOR HYDROCARBONS

Several different approaches have been studied for the
analysis and characterization of petroleum products in the
1970's. Mattson (6) studied the technique of fingerprinting
(individualizing) oil samples by infrared spectrometry. He
did not find this to be as useful as gas chromatography had
been. He determined the best method utilized both gas
chromatography and infrared spectrometry.

In two articles by Bentz (7)(8) on the identification

9
of oil samples, a multi-method approach was recommended.
When. thin layer' chromatography, gas chromatography,‘
infrared spectrometry and low temperature luminescence
were performed, oil sample identification would occur to
greater than 99% if the samples had a common origin.

In another article, Bentz (9) compared several methods
of oil spill identification. These were then ranked in
order of the most useful results obtained. He concluded
that gas chromatography and infrared spectrometry were the
best methods followed by fluorescence spectrometry.

Saner et.al. (10) found that thin layer chromatography
used in the analysis of waterborne petroleum oils, showed a
0.968 probability of correctly matching an oil spill
sample to a suspect oil sample in the sample set he used.

Fortier et.al.(ll) explored low temperature
luminescence spectrometry for the identification of fuel
oils. The samples were identified by comparison to a
visual overlay of the sample in question. The advantage of
this method is that both phosphorescence and fluorescence
are available. However the disadvantage is that a complete
picture of the total luminescence (both phosphorescence
and fluorescence) cannot be seen because only three
excitation wavelengths were used. The extremely low
temperatures required for phosphorescence can also cause
problems in utilizing this method in that most laboratories

do not have the means to cool and maintain a sample at

10
sub-zero temperatures during analysis.

Gas chromatography/mass spectrometry has been utilized
for the analysis of characteristic polycyclic aromatic
hydrocarbons in gasoline samples under controlled
distillation, evaporation and burning conditions by Mach
(12) . However, mass spectrometry requires that a clean
sample be analyzed which is seldom found in evidentiary
material. In some cases contaminants are present in such
large quantities that they mask the presence of the
accelerant. This is especially true for capillary gas
chromatography when the accelerant is in some type of
partially burned carpet. Unfortunately not only is this
the method most crime laboratories use, carpet samples from
fires are extremely common as well.

Saner et.al. (13) took the methanol extractable
fraction of oil from oil spills and analyzed it by liquid
chromatography. This method suffered from pollution and
weathering problems that a sample of oil from a spill would
undoubtedly expierence. The method could not match the
suspect oil to the oil spill sample in all the cases
studied.

FURTHER DEVELOPMENT OF FLUORESCENCE IN THE ANALYSIS OF
HYDROCARBONS

The 1980's showed increased interest in fluorescence

methods for the analysis of petroleum products. A computer

controlled instrument for performing multiparametric

In

11
fluorescence measurements was devised by Holland
et.al.(14). This set the stage to begin exploring this
type of methodology.

An early explorer of this idea was Lloyd et.al.(15),
who examined a collection of high molecular weight
petroleum products by sychronous fluorescence spectroscopy.
The objective of this study was to develop and evaluate
synchronous fluorescence as a standard technique to be used
in the analysis of such evidence. Synchronous fluorescence
views the fluorescence of a sample at mmltiple excitation
and emission wavelengths. Eight different samples drawn
from forensic science case work were analyzed. The results
showed that the same fluorescence characteristics are
present in most samples with sample differentiation being
dependent on the relative fluorescence intensities.
Samples from different sources could be differentiated by
visually comparing fluorescence intensities. Samples of
common origin looked markedly similar but could not be
discounted as having different origins. Samples were
reanalyzed over time with the same results. The authors
determined that synchronous fluorescence can be successful
in that common spectral patterns can be efficiently
recognized and retrieved with a low level of error.

Two articles by Kubic et.al.(16)(17) describe variable
separation synchronous excitation fluorescence. In this

method excitation and emisson wavelengths are scanned

12

simultaneously at different rates thus allowing multiple
views of the fluorescence spectra. This creates a
simulation of a three dimensional fluorescence spectrum
without plotting software. The first article applied this
method to the analysis of automobile engine oils (16) . In
the second article the authors attempted to distinguish
used automobile engine oils (17). All but 2 of the 45 oil
samples studied could be differentiated.

Blackledge et.al. (18) studied 16 commercial products
having a petrolatum base by liquid chromatography and
synchronous fluorescence spectrometry. He was able to
distinguish all 16 of the samples using as little as 0.5mg.
However, interferences from detergents and sizing used on
the clothing commonly encountered with this type of
evidence could occur. Infrared spectometry and proton
magnetic reasonance spectrometry were also used in this
study and were determined to have little value for
comparison purposes.

Warner et.al. (19) determined that for most pure
luminophores the emission spectrum is independent of the
excitation wavelength and vice versa. Petroleum products
are not pure luminophores, therefore it would be expected
that their emission spectra would vary depending on the
excitation wavelength used. This fact makes it desirable
to devise a method that can view the emission spectrum at

various excitation wavelengths thus enabling a more

13
complete picture of the total fluorescence of the sample.
As referred to previously Holland et.al.(14) had devised a
completely' automated. system. capable of simultaneous
absorption and fluorescence measurements, therefore
indicating that computer processing of such a
multiparametric method could be accommodated.

Siegel (20) proposed such a method called, (by the
manufacturer Perkin Elmer), three dimensional fluorescence
spectroscopy. Fluorescence properties vary with the
relative amounts and different types of polycyclic aromatic
hydrocarbons present in the sample. Therefore a method
that can view the fluorescence properties of a sample at
multiple wavelengths thus characterizing the total
fluorescence properties of the sample is valuable in the
comparison of two similar samples such as brands of
gasoline. Also data processing was introduced that would
subtract one three dimensional plot from another to further
clarify a comparison of two samples.

Duggan et.al.(21) recognized the need for a
multiparametric method to analyze multicomponent
environmental samples such as oil spills. His method
scanned the excitation and emission wavelength range of
interest only. The emission wavelength was scanned between
300 and 600nm while the excitation wavelength was stepped
up by 1nm between each scan. This completely characterizes

the fluorescence properties of very complex mixtures within

14
the specified excitation and emission wavelength range. A
computer with a program capable of plotting and storing all
the data collected was interfaced to the fluorimeter.

Three dimensional fluorescence was used to identify
major components of crude oil that had come in contact with
sea water by Ostgaard (22). Siegel et.al.(23) examined
motor oils and lubricants using three dimensional
fluorescence. In addition, the resultant three dimensional
emission stacked plots were compared by subtracting one
from another via computer rather than just by a visual
comparison. Ten motor oil and eleven lubricating oil
samples were tested. When subtracted, the plots of oils
with a common origin resulted in a flat plane indicating no
net fluorescence. However, when the plots of samples with
different origins were subtracted from each other a net
fluorescence was obtained resulting in a plot with "hills
and valleys". The authors concluded that the large amount
of spectral information generated and the ability to
manipulate it by computer, made three dimensional
fluorescence an effective method of comparison for motor
oils.

Three dimensional fluorescence was also evaluated by
Siegel et.al.(24) using gasoline samples. By utilizing the
subtraction program developed by Siegel the authors were
able to determine if two gasoline samples could have had a

common source. The study also addressed whether any common

15
features were present when comparing grades of the same
brand of gasoline or a group of gasolines of the same
grade.

Siegel et.al. (25) examined petrolatum based products
utilizing three dimensional fluorescence. The same
subtraction program was used to compare samples. The
authors concluded that the petrolatum products studied
could be differentiated by this method. In fact this
method has been used in actual forensic case work on more
than one occasion with successful results.

Mann (26) compared gasoline samples qualitatively and
quantitatively using capillary gas chromatography. It was
determined that gas chromatograms of neat gasolines
demonstrate variability. The authors claim that the
ability to discriminate among gasolines depends on
resolution in the C4 to C8 region of the chromatogram.
Mann concluded that this would be a good technique for
differentiating gasolines with different sources. In his
second paper Mann (27) discussed capillary gas
chromatography as it applies to actual case work. He
concluded that the region most important for the comparison
of two gasolines is altered before the gasoline is 40-60%
evaporated thus making comparison much less meaningful.
However it may still be able to be determined if two
gasoline samples have a different origin.

Guinther et.al.(28) analyzed gasoline at various

16
stages of evaporation. The authors used capillary gas
chromatography to analyze their samples. They concluded
that the least volatile components increase dramatically in
concentration as the gasoline is evaporated. This change
proved. to be reproducible thus allowing evaporated
gasolines to be isolated and identified as such.

Finally Siegel et.al.(29) studied 22 midrange
petroleum products (charcoal lighters, paint thinners and
synthetic solvents) by three dimensional fluorescence and
capillary gas chromatography. The samples were evaporated
and partially combusted. The authors found that three
dimensional fluorescence was much better at discriminating
among similar products than was capillary gas
chromatography, ‘which.rcould. only' put the products into
broad classes. They also found that when the samples were
partially or totally evaporated the three dimensional plots
could not be related back to the neat plot of the same
sample. However the three dimensional results were
consistent as long as the sample was evaporated to the same
degree. Combusted samples did not yield any useful
information by capillary gas chromatography. The
combusted samples did have informative three dimensional
plots except that the same plots could not be repeated on
subsequent burnings. The authors performed a blind test on
neat samples, which showed three dimensional fluorescence

to be the more reliable technique for determining whether

17
or not two samples were of the same brand.

The current study will further evaluate the
combination of the three dimensional fluorescence and
capillary gas chromatography methods in the analysis of
neat and evaporated gasoline samples. The gasolines were
evaluated based on the changes they exhibited in both
methods when they were subject to evaporation. Since
gasolines are complex mixtures of various multicomponent
entities the loss of the most abundant component of the
volatile hydrocarbons through evaporation should leave
behind the less abundant components that may not be
visible. These include the various additives that the
manufacturer and refinery add to the different gasolines
(30) as well as the higher molecular weight hydrocarbons.
These additives would be the most likely component of
gasolines to vary significantly between brands, grades and
lots. Therefore it may be possible to distingusih brands,
grades and lots with capillary gas chromatography and three

dimensional fluorescence spectroscopy.

mm
Materialsandnethgds

Nine brands and grades of gasolines were chosen for
this study. They were obtained from commericial sources
and stored in a refrigerator in brown glass screw cap
bottles. The samples were as follows: Mobil Unleaded,
Mobil Super Unleaded, Shell Regular, Shell Unleaded,
Standard Regular, Standard Unleaded, Standard Premium,
Total Regular and Total Unleaded. Spectrograde cyclohexane
(B&J) was employed as the solvent without further
purification. Fluorescence spectra and gas chromatograms

of cyclohexane showed no interference.

Glassware Preparation

Nonedisposable glassware, including pipettes,
volumetric flasks, beakers and quartz fluorescence
cuvettes, were prepared using the following procedure to
insure that residual fluorescence from a previous sample or
from cleaning would not be a problem.

1. Rinse once in fluorescence grade cyclohexane

2. Rinse once in acetone

3. Rinse once in distilled water

4. Rinse once in concentrated nitric acid

5. Rinse again in distilled water
6. Dry in a 60 C oven

18

19
Sample Preparation

1. Ten ul of gasoline were placed into a ten
m1 volumetric flask and diluted to the mark with
Spectrograde cyclohexane.

2. One ml of the solution prepared in step #1 was
placed in a second ten m1 volumetric flask and
diluted to the mark with Spectrograde
cyclohexane.

3. Step #2 was repeated using the solution made in
step #2. This was the final dilution to a
concentration of ten parts per million (ppm).

4. The solution made in step #3 was kept covered to
prevent evaporation and was analyzed within
twenty four hours.

Sample Analysis

The fluorimeter was a Perkin Elmer MPF-66
Spectrofluorimeter equipped with a Perkin Elmer Model 7300
Data Station and a PR-310 printer/plotter. The software was
a Perkin - Elmer "PECLS" data collection and plotting
program. Three dimensional spectra were obtained using the
"tlsm" software. Each sample was first prescanned using a
"scout" program to determine the range of excitation and

emission fluorescence and also the excitation and emission

maxima (Figures 4.1 and 4.2).

1. Emission was scanned from 250-400nm with the
excitation start at 200nm and the increment set at
4nm.

2. Excitation was scanned from 200-300nm with the
emission start at 250nm and the increment set at
5nm.

The gas chromatograph was a Varian Model 3300 equipped with
a Model 601 Data Station and a Hewlett Packard Thinkjet

Printer. The capillary column was a J & W DB-l, 30 meter

20
with a 0.25 micron coating. The chromatographic conditions

were as follows:

Initial column temperature - 50 degrees centigrade
Initial hold time - 4 minutes

Final column temperature - 200 degrees centigrade
Program rate - 10 degrees centigrade per minute

Final hold time - 6 minutes

Injector/detector temperature - 250 degrees centigrade
Injection volume - one microliter

Range - 11

DS attenuation - 128

Run time - 25 minutes

Obtaining Fluorescence Spectra

The Perkin Elmer Total Luminescence Spectroscopy III
package, PETLS III, was utilized to run, collect and plot
the three dimensional spectra. The fluorimetric conditions
were as follows:

Entrance slit - 5

Exit slit - 5

Scan speed - 240nm/min.

Response factor - 1

Emission slit - 3

Excitation slit - 3

Mode - ratio

Gain - lo

Emission filter - open
Evaporation of the Gasolines

Ten milliliters of the gasoline sample was placed into
a fifty milliliter beaker and placed in the fume hood. The
five milliliter point on the beaker was marked prior to
putting the gasoline in it. The gasoline was evaporated to
the mark for 50% evaporated. For the 100% evaporated
sample 10 milliliters of gasoline was placed in the beaker

and was allowed to evaporate completely. This residue was

reconstituted in Spectrograde cyclohexane and analyzed.

Quanta-arm
Results

Tables 1 - 3 list three dimensional fluorescence data for
each gasoline sample neat, 50% and 100% evaporated.

Figures 4.1 and 4.2 are an example of an emission and an
excitation scout spectrum.

Figures 4.3 - 4.11 are the capillary gas chromatograms of
the neat gasoline samples.

Figures 4.12 -4.20 are the capillary gas chromatograms of
the 50% evaporated gasoline samples.

Figures 4.21 - 4.27 are the capillary gas chromatograms of
the 100% evaporated gasoline samples.

Figures 4.28 - 4.36 are the three dimensional fluorescence
emission stacked plots of the neat gasoline samples.

Figures 4.37 - 4.45 are the three dimensional fluorescence
emission stacked plots of the 50% evaporated gasoline
samples.

Figures 4.46 - 4.50 are the three dimensional fluorescence
emission stacked plots of the 100% evaporated gasoline
samples.

Figures 4.51 - 4.58 are ‘various three dimensional
fluorescence subtraction plots.

21

22

Table 1

Innee Dimensional Fluorescenee gene fen fine Nee; Qeseline
Semnles

Excitation Emission Maximum
Gasoline Wavelength Wevelength Intensity
Mobil Unleaded 219 288 16.4
Mobil Super Unleaded 219 286 18.4
Shell Regular 217 285 10.0
Shell Unleaded 219 287 13.8
Standard Regular 219 288 20.2
Standard Unleaded 217 285 11.0
Standard Premium 217 287 14.4
Total Regular 217 289 480.6
Total Unleaded 219 289 20.6

Cyclcohexane Blank 255 276 105.0

23

Table 2

_nnee Qinenei_ne_ Flnoneseence Data fen the __3 Evanonaneg
_aselins §§EE_§§

Excitation Emission Maximum
geeeline Wavelengnh Wevelengtn Inneneiny
Mobil Unleaded 217 287 18.0
Mobil Super Unleaded 223 287 18.4
Shell Regular 217 287 16.4
Shell Unleaded 227 336 20.4
Standard Regular 221 288 26.8
Standard Unleaded 219 288 20.4
Standard Premium 221 289 20.0
Total Regular 217 288 15.4

Total Unleaded 221 289 21.4

24

Table 3

Three Qimensionel Fluorescence Qata for the 100% Evanoreted
mm

Excitation Emission Maximum
fieeeline Wavelengtn Wavelength Inteneity
Mobil Unleaded 265 361 15.6
Shell Unleaded 265 361 36.6
Standard Unleaded 233 344 15.2
Standard Premium 233 344 10.6

Total Unleaded 227 340 178.4

25

SCOUT PERKlN-ELMER MODEL MPF-66 EMISSION SURVEY REPORT REV 4.0

Incl-ulnnuuuununIIII-n.-unusual-lunnnucuuunuucnn
SAMPLE: SIBDGGFO DFGMIUM 98$ 10ppm DATE: Mar 27 1987 TIME: 10:38:00

EMISSION PEAK TABLE

1 2 3 4 5
WAVELENGTH: 288.6 321.4 336.4 238.6 0.0
INTENSITY: 12.19 3.30 2.68 0.68 0.00
status y
POIHIS EX WI 5115(X/M) From TO 1”! Min MEX Name
Y: 1011 222.0 5.0/ 3.0 232.0 - 434.0 0.2 0.01 12.20
Nous/Gain Corr Emfil Spa/Rap Indicators
RATIO/LO NO OPEN 120.0/1.0 F AC1

mam SMILE: standard pmiul ca: 1099: WE: lIar 27 198?

 

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Figure 4.1 Emission Scout Spectrum Of 10ppm Standard Premium Gasoline

26

SCOUT PERKIN-ELMER MODEL MPF-66 EXCITATION SURVEY REPORT REV 4.0

.-I.-nus-uluuncnnnI--------------I.cumulus-3.....-
SAMPLE: Standard prQMIum gas 10pm DATE: mr 27 1997 TIME! 10141325

EXCITATION PEAK TABLE

1 2 3 4 5
WAVELENGTH: 218.0 267.6 0.0 0.0 0.0
INTENSITY: 14.3 3.3 0.0 0 0 0.0
status 2
POIntS Em WI SltS(X/M) From TO Int Min Max Name
Z: 371 289.0 5.0/ 3.0 205.0 - 279.0 0.2 0.27 14.31
Moan/Gain Corr Emfil Spa/Rap Indicators
RATIO/LO NO OPEN 120.0/1.0 F AC1

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may;

CAPILLARY GAS CHROMATOGRAPHY

In comparing capillary gas chromatograms of the neat
gasoline samples (Figures 4.3-4.11) it becomes immediately
apparent that all of the gasoline samples look very
similar. In addition to this there are several peaks in
each chromatogram which would make a peak by peak
comparison very tedious and time consuming. Even if a
computer program was designed to do a peak by peak
comparison, the major groups of peaks elute at
approximately the same time from the column. There are
major groups of peaks with the following retention times on
the chromatograms of all the gasoline samples: 1-3
minutes, 5-6 minutes, 7-8 minutes and several small peaks
having similar retention times greater than 8 minutes.
Clearly, in this comparison the gasolines cannot be
differentiated by capillary gas chromatography.

The capillary gas chromatograms of the 50% evaporated
gasoline samples (Figures 4.12-4.20) also look very
similar. The mid range peaks appear to have gotten
stronger due to the loss of the lower boiling point
fraction at the front end of the chromatogram.
Unfortunately these losses are seen in all the gasoline

samples with the major peak groups still present at the

83

84

same retention times that they were prior to evaporation.
There also still remains several peaks giving several
points of comparison. Although some of the unleaded and
premium grade gasolines show more intense peaks in the 7-8
minute retention time range, the 50% evaporated Shell
unleaded gasoline (Figure 4.15) does not look any different
in this area than does the 50% evaporated Shell regular
gasoline (Figure 4.14). Therefore even in such a small
sample size as this no common patterns are observed when
looking at gasoline samples of the same grade. Again the
gasoline samples cannot be differentiated by capillary gas
chromatography.

After total evaporation the capillary gas
chromatograms of the gasoline samples, (Figures 4.21-4.27),
still look very similar within the same brand. For example
Total unleaded (Figure 4.27) and Total regular (Figure
4.26) look very similar. However, they look different from
the Mobil brand (Figures 4.21 and 4.22) or the Standard
brand (Figures 4.23-4.25). Whether brands could be
differentiated when they are 100% evaporated by this
technique routinely cannot be determined by this study.
However, differentiating between grades within a brand is
not possible in the samples studied here. Capillary gas
chromatography appears to be a useful technique ‘ in
distinguishing different types of petroleum products. Also

the possibility exists in the analysis of the totally

85
evaporated gasoline samples of distinguishing brands as

well.

THREE DIMENSIONAL FLUORESCENCE SPECTROSCOPY

Comparison of the three dimensional emission stacked
plots of the neat gasoline samples, (Figures 4.28-4.36),
were accomplished. by direct visual comparison, the
subtraction program and by Tables 1-3 which show each
gasoline's excitation and emission wavelength at maximum
intensity. Simply by viewing the tables it is apparent
that the gasolines are very similar in that several have
the same excitation and emission wavelengths or wavelengths
that only differ by one or two nanometers. This is why the
direct visual comparison is necessary to distinguish the
samples by being able to view the entire range of
fluorescence not just the wavelenghts at maximum intensity.
This is especially so in the case of some of the 100%
evaporated samples, even though their wavelengths are
identical the total fluorescence emission stacked plots are
completely different by visual comparison.

Clearly from these observations the neat gasolines can
easily be differentiated from each other. However, there
does not seem to be any similarity between the same grades
of different brands in their fluorescence properties such
that one could say, for example, that all the unleaded

gasolines showed a certain characteristic fluorescence peak

86
that the other grades did not. This same conclusion was
reached by Siegel et.al. (24) in their study of the
analysis of neat gasoline samples by three dimensional
fluorescence.

The three dimensional fluorescence emission stacked
plots of the gasoline samples after 50% evaporation
(Figures 4.37-4.45), could easily be related to their
corresponding neat plot. This was accomplished by simple
visual comparison. In some cases the 50% evaporation made
two samples easier to distinguish, Mobil and Shell unleaded
for example (Figures 4.37 and 4.40) but in other samples
the 50% evaporation made them more difficult to distinguish
such as Mobil unleaded and Shell regular (Figures 4.37 and
4.39) or Mobil unleaded and Total regular (Figures 4.37 and
4.44).

The three dimensional emission stack plots of the
totally evaporated. gasoline samples (Figures 4.46-4.50)
looked dramatically different from either their neat or 50%
evaporated counter parts. All of the totally evaporated
gasoline samples were readily differentiated from each
other by direct comparison of their three dimensional
emission stacked plots. However, they could not be
compared back to their respective neat or 50% evaporated
plots. These agree with the findings of Siegel et.al. (29)
on the partially and totally evaporated mid-range petroleum

products they analyzed by three dimensional fluorescence.

87
The gasoline samples studied here did not show consistent
patterns of fluorescence characteristics within the same
brand or grade.

The theory behind the three dimensional fluorescence
analysis of totally evaporated gasoline samples is that the
components left behind that fluoresce after the lighter
volatile hydrocarbons are evaporated off are the high
molecular weight polynuclear compounds which contain the
most fluorescence. The fluorescence of these compounds
seem to be hidden by the fluorescence of the lighter
volitle hydrocarbon fraction as is illustrated by the fact
that the 100% evaporated three dimensional fluorescence
plots look so dramatically different from either the neat
or the 50% evaporated plots.

The following examples illustrate how, by the use of
all the data generated by this study, it is possible to
distinguish these gasoline samples. Standard premium and
Standard unleaded were the most similar of all the samples
studied. They looked similar chromatographically and in
their three dimensional fluorescence emission stacked plots
both neat (Figures 4.33 and 4.34) and 50% evaporated
(Figures 4.42 and 4.43). However, even though they had the
same excitation and emission wavelengths at maximum
intensity when 100% evaporated their three dimensional
emission stacked plots were visually different. Even when

these samples’ three dimensional emission stacked plots

88
were subtracted neat, 50% and 100% the resultant plots
showed no substantial differences (Figures 4.51-4.53) with
the Pearson's Q being very close to one. For the other
samples either direct visual comparison or the subtration
program or both could distinguish them.

For example, Total regular and Shell regular had very
similar three dimensional emission stacked plots both neat
(Figures 4.35 and 4.30) and 50% evaporated (Figures 4.44
and 4.39) . However, when the neat plots were subtracted
from each other the resultant plot showed substantial
differences and a lower Pearson's Q (Figure 4.54). In the
case of Mobil unleaded and Shell unleaded, the resultant
subtration plot of the neat three dimensional fluorescence
emission stacked plots (Figure 4.55) showed these samples
to be very similar with a high Pearson’s Q. However, when
their 50% (Figures 4.37 and 4.40) and 100% (Figures 4.46
and 4.47) evaporated three dimensional emission stacked
plots are visually compared, they do not look similar at
all. The Total unleaded and Shell regular gasolines showed
no major differences when their neat three dimensional
emission stacked plots were subtracted (Figure 4.56) but
upon visual comparison of the neat (Figures 4.36 and 4.30)
and 50% (Figures 4.45 and 4.39) evaporated plots these
samples do not look similar. Similarly the subtraction
plot of the neat Mobil super unleaded and the 50%

evaporated Mobil super unleaded (Figure 4.57) shows enough

89
differences and a low enough Pearson's Q that one may
conclude that they have a different source. However, upon
visual comparison of the three dimensional fluorescence
emission stacked plots it is obvious that they are very
similar (Figures 4.29 and 4.38). When two samples that
have completely different three dimensional fluorescence
emission stacked plots are subtracted, such as 100%
evaporated Total unleaded (Figure 4.50) and 100% evaporated
Standard unleaded (Figure 4.48) , the resultant plot shows
major differences and a very low Pearson's Q (Figure 4.58).
These examples serve to illustrate that one piece of
information is not enough to characterize a multicomponent
mixture such as gasoline. All of the information generated

must be evaluated in order to reach the proper conclusion.

CONCLUSION

This thesis shows promise in characterizing neat, 50%
and 100% evaporated gasoline samples by three dimensional
fluorescence spectroscopy. Each of the samples analyzed
showed dramatically different fluorescence characteristics
not only from each other but also from themselves after
evaporation. It is certainly a much more powerful
technique in this regard than is capillary gas
chromatography as is illustrated here. Further study is
required to establish the reproducability of three

dimensional fluorescence analysis of evaporated gasoline

90
samples. Furthermore, more different brands and their
respective grades require analysis by this technique to
establish or discount any fluorescence patterns that may or
may not be present in a specific brand or grade.

A study which focuses on the reproducability of the
analysis conducted here would be a logical progression of
this work. If the methods and results cannot be duplicated
then their use in the analysis of neat and evaporated
gasolines must be seriously questioned. Furthermore, this
study involved only nine different brands of gasolines.
There are certainly more than that in the United States

alone, hence more brands need to be analyzed as well.

(1)

(2)

(3)

(4)

(5)

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