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I, If. _._—— . _._ - — -—— < ——-—~ MICHI IGAN STAT II I II II IIIIIIIIIII'IIIII IIIIIIIIIII This is to certify that the thesis entitled HEAT INDUCED DESORPTION 0F VOLATILES FROM SUSCEPTOR MATERIAL presented by SUE ANDERSON ROUSSELO has been accepted towards fulfillment of the requirements for _MasreLs—_degree in MEL Wfl-flq/g— Major professor Bruce R. Harte, Ph.D. Date 2 l 90 0-7639 MS U is an Affirmative Action/Equal Opportunity Institution LIBRARY locum State University J ‘I PLACE IN RETURN BOX to remove this checkout from your record. TO AVOID FINES return on or before date due. DATE DUE DATE DUE DATE DUE HUN: 3 mil J 23 04 .:I— = —II fil I MSU Io An Affirmative Action/Equal Opportunity Institution cmm1 : r?! "‘ ' w ' HEAT INDUCED DBBORPTION O? VOLBTILBB PROM BUBCBPTOR MATERIAL BY 8ue Anderson Rousselo A THESIS Submitted to Michigan state University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE school of Packaging 1990 ABSTRACT HEAT INDUCED DESORPTION OE VOLATILES PRON SUSCEPTOR MATERIAL BY Sue Rousselo Susceptor material was analyzed to detect the presence of volatiles desorbed upon heating using static headspace and diffusion trapping techniques. The susceptor board was cut into specified sizes and placed into a glass vial which was then sealed. Static headspace analysis was performed using samples heated in the microwave on full power for time periods ranging from five to seven minutes and in an oil bath at temperatures ranging from 200'C to 240‘ C for five minutes. Diffusion trapping analysis was performed on samples heated in an oil bath at temperatures ranging from 200' C to 240' C for five minutes using a "Tenax trap”. The temperature experienced by the susceptor in the oil bath was determined using a thermocouple and in the microwave was determined using Luxtron probes and a Hughes Infrared camera. six major components ‘were detected (2-methy1-l-propanol, n-butanol, styrene, 2-butoxy-l-ethanol, furfural, 2-(2-butoxyethoxy) ethanol) and quantified using a gas chromatographic technique, and their identities confirmed using mass spectroscopy. Copyright by SUE ANDERSON ROUSSELO 1990 To Ken, my mother and father for their support. iii ACKNOWLEDGEMENTS I would like to thank Dr. Bruce Harte, my advisor, for his guidance, support and encouragement. I would also like to thank Dr. Jack Giacin and Dr. Parvin Hoojjat for sharing their time and expertise in methods development and interpretation of the results. I would like to express my sincere appreciation to Dr. James Booker from the James River Corporation for teaching me the method of diffusion trapping and for always being available to answer questions. Many thanks also to Dr. Booker and Dr. Matt Zabik for their help in performing the mass spectrometry analysis. I would also like to thank the 0.8. Department of Agriculture-Center for Environmental Toxicology (CET) and.the Center for Food and Pharmaceutical Packaging Research (CFPPR) for their financial support which made this study possible. Finally, I would like to express my deepest thanks to my husband, Ken, and to my parents for their love and support. iv TABLE OF CONTENTS Introduction Literature Review The Nature of Microwaves Dielectric Constant, Loss and Loss Tangent Parameters which Control the Heating Effect in the Microwave Heat Generation in a Microwave Oven - Ionic Conduction and Dipole Rotation Food Formulations used to Achieve Drowning in the Microwave Types of Microwave Packaging Types of Susceptors Theory of Migration of Indirect Food Additives Measurement of Package Material Temperature During Microwaving Analytical Methods for Determining Volatile Migrants from Susceptor Packages Volatile Migration Studies Materials and Methods Susceptor Packaging Material The Power Level of the Microwave Oven Conditioning the Tenax GC‘ Temperature Profile of Susceptor During Heating an Oil Bath 10 11 15 17 19 23 25 29 29 31 31 Temperature Profile of Susceptor During Heating in the Microwave Temperature Profile of Susceptor Surface Utilizing a Hughes Thermal Video System Static Headspace Technique for Measuring Volatiles Released from the Susceptor During Microwaving Diffusion Trapping Technique for Measuring the Release of Volatiles from the Susceptor During Conventional Heating Headspace Technique for Measuring the Release of Volatiles from the Susceptor During Conventional Heating Identification and Confirmation of Volatiles using Mass Spectrometry Quantification of Volatiles using External Standard Curves Results and Discussion Oil Bath Time vs. Temperature Correlation Microwaving Time Vs. Temperature Correlation Hughes Infrared Camera Temperature Profile Quantification Using External Standard Curves Volatiles Released During Microwave Heating of the Susceptor Quantified Using the Static Headspace Technique Volatiles Released from Susceptor Heated in an Oil Bath using the Diffusion Trapping Technique Volatiles Released from Susceptor Heated in an Oil Bath - Static Headspace Technique Mass Spectrometry Identification Conclusion vi 32 34 35 37 39 4O 41 43 43 57 57 62 72 76 82 86 Appendices Appendix A Appendix 8 Appendix C Appendix D Calibration Curves for Volatiles Sample Calculation Sample Calculation Sample Calculation vii 95 96 97 Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Figure 10. LIST 0? FIGURES A Plane Monochromatic Electromagnetic Wave. Composition of a Susceptor. Schematic of Diffusion Trapping Technique. Temperature Profile of Susceptor During Heating in an Oil Bath at Specified Temperatures for seven min. Temperature Profile of Susceptor During Heating at Full Power for seven min. in the Center of a Tappan microwave oven with and without a water load. Temperature Profile of Susceptor During Heating at Full Power for seven min. in the Hot Spot of a Tappan microwave oven with and without a water load. Hughes IR Thermal Map. Hughes Probeye Infrared Temperature Profile of Susceptor During Heating at Full Power for four min. in a Litton Generation II microwave oven with and without a water load. Quantity of Volatiles Released from Susceptor Material During Heating for five min. at Full Power in a Tappan (650 watt) microwave oven vs. an Amana (700 watt) microwave oven. Quantity of Volatiles Released from Susceptor Material During Heating for seven min. at Full Power in the Hot Spot of a Tappan microwave oven with and without a water load. 13 38 47 53 54 60 61 65 68 Figure Figure Figure Figure Figure Appendix A Figure Figure Figure Figure Figure Figure 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. Quantity of Volatiles Released from Susceptor Material During Heating in a Tappan microwave oven for seven min. at Full Power in the Hot Spot vs. the Center. Quantity of Furfural Released During Heating at Various Oil Bath Temperatures for five min. Measured Using Diffusion Trapping Technique. Quantity of Styrene Released During Heating at Various Oil Bath Temperatures for five min. Measured Using Diffusion Trapping Technique. Quantity of Volatiles Released During Heating in a 230° C Oil Bath for five min. measured using Diffusion Trapping vs. Static Headspace Techniques. Quantity of Furfural Released During Heating in an Oil Bath at Various Temperatures for five min. measured using Diffusion Trapping vs. Static Headspace Techniques. Calibration for z-Methyl-l-Propanol. Calibration for n-Butanol. Calibration for Styrene. Calibration for 2-Butoxy-l-Ethanol. Calibration for Furfural. Calibration Ethanol. for 2-(2-ButoxyEthoxy) ix 71 77 78 83 84 89 90 91 92 93 94 Table Table Table Table Table Table Table Table Table Table 10. TABLE OF TABLES Temperature of Susceptor Material During Heating in a 200' C Oil Bath for five min. Temperature of Susceptor Material During Heating in a 210' C Oil Bath for five min. Temperature of Susceptor Material During Heating in a 220' C Oil Bath for five min. Temperature of Susceptor Material During Heating in a 230° C Oil Bath for five min. Temperature of Susceptor Material During Heating in a 240' C Oil Bath for five min. Temperature of Susceptor Material During Heating at Full Power for seven min. in the Center of a Tappan Microwave Oven with a 250 ml Water Load. Temperature of Susceptor Material During Heating at Full Power for seven min. in the Center of a Tappan Microwave Oven in the Absence of Water. Temperature of Susceptor Material During Heating at Full Power for seven min. in the Hot Spot of a Tappan Microwave Oven with a 250 ml Water Load. Temperature of Susceptor Material During Heating at Full Power for seven min. in the Hot Spot of a Tappan Microwave Oven in the Absence of Water. Temperature of Frozen Microwave Pizza Susceptor Travauring Heating at Full Power for seven min. in the Center of a Tappan Microwave Oven. 44 44 45 45 46 48 49 51 52 55 Table Table Table Table Table Table Table Table Table Table 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. Temperature of Susceptor Sample Used for Diffusion Trapping During Heating at Full Power for seven min. in the Hot Spot of a Tappan Microwave Oven in the Absence of Water. Temperature of Susceptor Material During Heating at Full Power for four min. in a Litton Generation II Microwave Oven with and without Water Measured using a Hughes Probeye Infrared Temperature Camera. Volatiles Released During Heating of Susceptor Material at Full Power for five min. in the Center of an Amana Microwave Oven with a 250 ml Water Load. Volatiles Released During Heating of Susceptor Material at Full Power for five min. in the Center of an Amana Microwave Oven in the Absence of Water. Volatiles Released During Heating of Susceptor Material at Full Power for five min. in the Center of a Tappan Microwave Oven with a 250 ml Water Load. Volatiles Released During Heating of Susceptor Material at Full Power for five min. in the Center of a Tappan Microwave Oven in the Absence of Water. Volatiles Released During Heating of Susceptor Material at Full Power for seven min. in the Center of a Tappan Microwave Oven with a 250 ml Water Load. Volatiles Released During Heating of Susceptor Material at Full Power for seven min. in the Center of a Tappan Microwave Oven in the Absence of Water. Volatiles Released During Heating of Susceptor Material at Full Power for seven min. in the Hot Spot of a Tappan Microwave Oven with a 250 ml Water Load. Volatiles Released During Heating of Susceptor Material at Full Power for seven min. in the Hot Spot of a Tappan Microwave Oven in the Absence of Water. xi 58 59 63 63 64 64 67 67 69 70 Table Table Table Table Table Table Table Table Table Table Table 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. Volatiles Released from Susceptor Material During Heating in a 200° C Oil Bath for five min. - Diffusion Trapping Technique. Volatiles Released from Susceptor Material During Heating in a 210° C Oil Bath for five min. - Diffusion Trapping Technique. Volatiles Released from Susceptor Material During Heating in a 220° C Oil Bath for five min. - Diffusion Trapping Technique. Volatiles Released from Susceptor Material During Heating in a 230° C Oil Bath for five min. - Diffusion Trapping Technique. Volatiles Released from Susceptor Material During Heating in a 240° C Oil Bath for five min. - Diffusion Trapping Technique. Volatiles Released from Susceptor Material During Heating in a 200° C Oil Bath for five min. - Static Headspace Technique.‘ Volatiles Released from Susceptor Material During Heating in a 210° C Oil Bath for five min. - Static Headspace Technique. Volatiles Released from Susceptor Material During Heating in a 220° C Oil Bath for five min. - Static Headspace Technique. Volatiles Released from Susceptor Material During Heating in a 230° C Oil Bath for five min. - Static Headspace Technique. Volatiles Released from Susceptor Material During Heating in a 240° C Oil Bath for five min. - Static Headspace Technique. Relative Abundance of Ions Present in Susceptor versus a Standard Solution. xii 73 73 74 74 75 79 79 80 80 81 85 INTRODUCTION Microwave packaging has developed at an increasingly rapid rate as a result of changes taking place in the market due to consumer demand. Market penetration for microwave ovens is projected to be 91% by the turn of the century (Nazario, 1990) . Future growth is expected to occur as microwave ovens are purchased for the workplace, microwaveable shelf stable packages are placed in vending machines, and.as a second microwave is acquired for home usage. Due to the increasing number of women in the workforce, there is an ever- increasing number of dual career couples. These consumers are demanding a higher quality food product, which can be conveniently and quickly prepared in the microwave. In the past, a maj or drawback to cooking in the microwave has been an inability to cause browning and crisping of the food product. The temperature required to achieve browning of the food surface is above 300' F (149' C) for a significant portion of the cooking time (Sacharow, 1988). One way in which this problem has been overcome is with the use of susceptor packaging. In general, susceptors consist of metallized polyester laminated to paper or paperboard. The metallized portion of the structure is typically aluminum 2 (Perry, 1987). In controlled thicknesses the aluminum will not reflect microwave energy but rather couples with the electrical field to cause heating. In susceptor packages locallized heating of 450-500 ’F (232-260‘ C) is attained (Larson, 1988). At present, materials such as plastics, paperboard and composites are used for manufacturing microwaveable containers. When these materials are placed in contact with a hot food product, migration of substances in the package material can occur. If these migrants are absorbed by the food product, they may affect the safety and quality of the food. Currently, the Code of Federal Regulations for indirect food additives, resulting from migration of components of the package, range from frozen food temperatures to retort.cooking temperatures (250’ F or 121' C) (Erickson, 1989). At the temperatures attained during microwaving of susceptors there is no applicable regulation (Schiffman, 1988). Schwartz commented during the FDA public meeting on microwave susceptors "that the FDA does not have an upper temperature 'use limit in its regulations which cover microwave packaging materials - including regulations dealing with resinous and polymeric coatings and components of paper and paperboard in contact with aqueous and fatty foods" (Mitchell, 1988) . Hollifield noted that studies by the FDA on susceptor packaging materials indicate that cracking and.melting of the 3 polyester film occurs, leading to the direct exposure of the product to paper and adhesive layers in the susceptor (Mitchell, 1988) . Without a functional barrier, package components from the paper and adhesive may become indirect food additives. The safety of microwave susceptors has been questioned through recent articles in publications such as the Wall Street Journal (Nazarrio, 1990), Detroit Free Press (MacVean, 1990), Lansing State Journal (Whyche, 1989) and the unsignal Examiner (anon., 1990). The Center for Science in the Public Interest, a non-profit organization, has urged consumers to avoid microwaveable packages containing susceptors (Hazario, 1990) . In this study, the primary focus has been to develop and compare test methodologies which can be used to identify and quantify the level of migration of volatile package components from susceptor package material. The specific objectives of this study were as follows: 1. To determine the effect of various heat treatments on the desorption of package components during conventional heating using the diffusion trapping methodology. 2. To compare the sensitivity and validity of the diffusion trapping technique with a static headspace technique. 3. To use infrared imaging and Luxtron Fluoroptic thermometry to "map" temperatures reached on the susceptor surface during microwave heating. LITERATURE REVIEU The Nature of Microwaves Microwaves are an example of an electromagnetic wave or field. Microwaves propagate as a wave travelling in the x- direction as shown in Figure l. The ”electric” field is oriented in the y-direction and is expressed in volts per meter (or cm). This field interacts with dielectric materials such as food and metals. The "magnetic” field is oriented perpendicular to the ”electric" field, and interacts primarily with ferrous metals. Susceptor film consists of a thin polyester film onto which a thin layer of aluminum or stainless steel has been deposited. Absorption of the microwave energy by the metallized layer causes the susceptor to heat. When the electric field is applied to»a small metal particle, a current will flow until the charge distribution on the particle produces the exact opposite charge of the applied field, such that the total field existing within the metal particle is zero (Lorenson, 1989). ‘The electric field, which is changing its polarity (or charge) at microwave frequencies, causes an oscillating current to be established in the metal particle. Since the metal particles are thin, they will have a high electrical resistance and will be heated by this current 2&5 8.88.288 8.59680: 29a < .. 2:9,... (Lorenson, 1989). Electromagnetic waves are characterized by both their frequency and wavelength. The "wavelength" is the distance between two adjacent points in the.same or similar field. This is similar to the distance between adjacent peaks of water waves. Wavelength is expressed in meters (or cm). The frequency is dependent on both the wavelength and the distance electromagnetic waves travel in one second. The velocity of all electromagnetic waves is 3 x 10m cm/sec. Therefore, the frequency is equal to the distance the wave moves in one second (c) divided by the distance between field peaks (1): f-9_ (1) l The electromagnetic spectrum includes various wave forms such as visible light, infrared, microwaves and radio in order of decreasing frequency or increasing wavelength. The wavelength of microwaves is between visible light and household electricity. A frequency of 2450 MHz is commonly used in microwave ovens (Osepchuk, 1975). Dielectric Constant, Loss and Loss Tangent There are two parameters which describe a material's ability to absorb heat in the microwave. These parameters are the dielectric constant (e') and the loss factor (6"). The dielectric constant is a measure of the speed of electromagnetic waves as they travel through a material. This 7 is a measure of a material's ability to store energy. The loss factor describes a material's ability to dissipate the electrical energy as heat (Tinga, 1970). The loss tangent (6) is the ratio of the loss factor to the dielectric constant: he; (2) 6 The loss factor and loss tangent.are used to describe the "lossiness" of a material. As the loss terms increase, the amount of energy that a material will absorb increases. Therefore, the larger the "lossiness" of’a material, the more power it will absorb which causes a higher temperature increase in the food (Perry, 1987). Parameters which control the Heating Effect in the Microwave Oven The two most important characteristics of a food product which affect its dielectric constant are moisture and salt content. Materials which have molecular dipoles, mobile ions or mobile electrons are affected by the electrical field in the microwave. The dipoles and ions are "excited" by the oscillating microwave field. The friction created by the movement of these molecules causes the heating effect. Both water molecules and salts will cause an increase in heating as they try to align themselves with the electrical field (Perry, 1987). Salt ions add to the dipole and increase the oscillation rate. Sugar is mildly polar and will also add to the dipole effect (Sheath, 1988). 8 Long chain fatty acids of fats and oils are relatively nonpolar. Their behavior in the microwave is determined by their specific heat. Specific heat is the amount of energy needed to raise product temperature by If C. The specific heat compares the ability of a product to hold heat to the ability of water (Sth-l) to hold heat. The Sth of most fats and oils is 0.5. The lower the specific heat of a material, the greater the temperature increase of the material when heated (Shaath, 1988). Package geometry can also play a key role during heating of food products in the microwave. There is a tendency for heating to be concentrated near the walls of the container with much cooler central regions within the product (Mudgett, 1988) . The edges of a product/package receive microwave energy from two! directions (top, side) which. can cause overheating. Corners receive microwave energy from three directions (top, two sides) which can be even more severe. Other areas of the package receive microwave energy from only one direction (top) and thus uneven heating can occur., The optimum shape for heating of a microwave container is circular. In this design, there are no corners which will overheat, and the distance to the center of the product is minimized (Amini, 1988). Square, rectangular and triangular shapes should be avoided unless the corners are ”rounded". Product shape, mass and thickness can also affect heating in the microwave. Quite often, product shape is determined 9 by the package geometry. As described above, edges and corners can be overheated. If the product is very thick, the center will remain cool. Thin portions of the material will tend to heat faster. The mass of the material or "load" also has an effect, since the greater the mass the longer the cooking time required. For example, heating three baked potatoes instead of one will take nearly three times as long in the microwave oven (Osepchuk, 1979). Heat Generation in a Microwave Oven - Ionic Conduction and Dipole Rotation Ionic conduction occurs when water molecules break apart to form a positive H ion and a negative 0H ion. This occurs at room temperature with about one in ten million water molecules. The positive H ion will combine with a water molecule to form an H,O ion. The DH ion retains the electron which belonged to the H ion. Therefore, both ions are electrically charged and will try to align with the oscillating’ electrical field. creating’ a flow' of current (White, 1973), which is kinetic energy. When these ions collide with water molecules they give up their kinetic energy. These molecules may collide thousands of times during their exposure to microwaves. When these molecules collide the kinetic energy is converted into heat. The field may be either continuous or intermittent: ionic conduction will occur in either case. The ions are accelerated by fields and energized upon impact with other ions (White, 1973). 10 Dipole rotation has major dependency on the microwave frequency and temperature of the product (White, 1973). Due to the nonspherical shape of the dipolar molecules, rotation is limited and orientation is randomized. As the microwave field propagates during microwave heating, the orientation of the molecules becomes ordered. When the field dies down the orientation once again becomes random. During dipole rotation, there is a conversion of energy from electric field energy to stored potential energy and then to stored random kinetic or thermal energy in the material. The energy conversion becomes most efficient when the time intervals of application and removal of the electric field (frequency) coincide with the time required for build up and decay of the induced order (White, 1973). Orientation and decay time is dependent on both temperature and. molecular size. This is known as the relaxation frequency. At higher temperatures, orientation and decay'occur’more rapidly; For small molecules such as liquids and monomomers, the relaxation frequency is greater than the microwave frequency. As product temperature increases there is a slowing down of energy conversion into heat. For larger ‘molecules like polymers, however, the relaxation frequency is lower than the microwave frequency which results in a faster conversion of microwave energy into heat (White, 1973). Food Formulations used to Achieve Drowning in the Microwave The high temperature air in a conventional oven results 11 in dehydration and browning of a food product's surface. In a microwave oven, the air surrounding the product is not directly heated. The excitation of polar molecules such as water are responsible for the heating effect. When moisture contacts the cool oven air it condenses causing soggy product surfaces. Flavor companies have developed flavors based on chemicals identified in the Maillard reaction to generate caramelized flavors. Two commonly used flavorants are methyl-and dimethylhydroxy furanone (Van Osnabrugge, 1989). The majority of flavor chemicals evaporate during microwave cooking. These chemicals must therefore be added at high concentrations which results in greater costs. Salts and coloring compounds have been used to induce chemical browning in roasted meat products. Salts and sugars have also been used to raise the surface temperature, enhance coloration and induce a degree of crisping in meat items (Andrews, 1988). Addition of chemical agents to a product changes the dielectric constant of the food at its surface so that the microwave energy has a greater heating effect. By changing the dielectric constant, the wavelength at the food surface is converted to infra-red so that browning can occur (Andrews, 1988) . Temperatures in excess of 140' C have been attained using susceptor pastes and liquid browning agents which are based on salt and calcium chloride compounds. In order to obtain an adequate hot plate effect, however, the temperature should be at least 160' C (Andrews, 1988) . 12 Types of Microwave Packaging Four types of microwave packaging materials are currently available. These are transparent, shielding, absorbing and modifying. Transparent materials allow microwaves to penetrate directly through the package and into the food product. This allows direct microwave heating to occur. So long as water is present, temperatures will be limited to 100' C (Perry, 1987) . As product temperature increases, the package material temperature will rise due to conduction from the product. Microwave transparent materials include polyethylene, polypropylene, polyester (including crystallized PET), polystyrene, glass and paper. Microwave packaging materials can also be used to "shield" the food product. Shielding materials are composed of metallic structures which are thick enough so as not to heat but to reflect energy away from the product. These materials can be used to prevent electromagnetic waves from reaching a product or areas of a product. A shield could be foil, foil laminated to a substrate, or any metal sheet converted into pans and trays (Perry, 1987). Field modifying materials focus and intensify microwave energy to allow for selective heating of a food product. The Micro—Match' Alcan System consists of a standard aluminum pan with a Micromatch lid. The smoothwall lacquered foil container has a well defined standing wave pattern in the microwave. The dome is Q composite structure of plastic and 13 59:. I] 3.823.. // 33896 a .o 523950 .u .591 ////////////////////////////// .................... .eu. uses-.ue-e.sane. .a. s, ‘aun .............. 525:3: EE Bag—om \II 14 strategically placed aluminum used to intensify product heating. The aluminum on the dome acts as an antenna system which tunes in microwave energy at the proper frequency in selected areas (Drennan, 1987). Absorbing materials (susceptors) are used to achieve browning and crisping in the microwave. Turpin (1980) defined susceptors "as a material which absorbs microwave energy by coupling with the electric field component of the microwave irradiation and through resistive heating in the thin film, microwave energy is converted into sensible heat." Susceptors are generally composed of metallized polyester laminated to paper or paperboard (see Figure 2). The metallized portion is typically composed of aluminum. Stainless steel is sometimes used instead of aluminum due to its higher resistance to oxidation. Aluminum will oxidize over a shorter time period to produce a nonmagnetic oxide. The nonmagnetic oxide will cause heating to cease. Stainless steel has an upper temperature limit of 425' F (218' C). The metallized portion is vacuum deposited in controlled optical density onto the polyester substrate. An optical density of 0.12 absorbs little of the microwave energy and causes insufficient heating. Densities between 0.18 and 0.29 are best for crisping and browning. These densities allow coupling with the electrical energy field in the microwave. Heavier depositions will cause microwave energy to be reflected causing arcing (Martin, 1988). 15 The polyester is used as a substrate primarily to serve as a food contact layer. From 48- to 92-gauge PET is most common (Martin, 1988). The metallized film is then adhesive laminated to the paper or paperboard which provides mechanical support. The metallized surface is laminated to the paper to prevent direct contact of the aluminum with the food product. This is done to protect the aluminum from.chemical or physical damage and to prevent the aluminum from becoming an indirect additive (Perry, 1987). Types of Susceptors New concepts in susceptor packaging include the use of susceptors in pressure-sensitive label forms, ULTEM' resin susceptor film, dual-mode susceptors, fibrous susceptors and flake-coated susceptors. Avery Label Industrial Products Division has developed a metallized polyester pressure sensitive label which acts as a heat susceptor. This label can be applied to boxes, bags, lids or other package components. It allows differential heating to occur within a package by precisely positioning the susceptor label within the food package (anon., 1987). GE Plastics has developed a new susceptor film which uses ULTEM ' resin. This resin is an amorphous thermoplastic polyetherimide. It is metallized in a vacuum deposition process, and can generate higher heat in lower optical densities than traditional susceptors. This film can reach higher temperatures in shorter cooking times to provide a 16 crisper food product. This resin has high heat resistance which will decrease cracking and crazing. It also has a high glass transition temperature (426' F or 219° C) which causes it to resist softening below 426' F (Stulga, 1989). DuPont is developing dual-mode susceptors, fibrous susceptors, and flake-coated susceptors (Huang, 1987). The dual-mode susceptor is designed to decrease hot and cold spots in the microwave. These uneven heating patterns are caused by nonuniform standing waves within the oven cavity. With traditional susceptor technology, the susceptor couples only with the electrical field component of the electromagnetic spectrum. The magnetic field strength maximum is always at the electric field minimum. Dual-mode susceptor materials heat both by coupling with the magnetic and electrical fields. The fibrous susceptor was developed to act as a deep fat fryer which lets moisture escape while keeping flavor inside the package or product. These susceptor materials are moisture permeable. The composition and construction is used to control the partition of the microwave energy between the surface and the inside of foods being cooked (Huang, 1987). 'The porous material allows the package to hold the flavor in. The flake-coated susceptor can be printed to different levels of microwave transmission and absorption. The heat flux in the microwave oven is controlled and adjusted by variations in flake material, flake size and shape, flake thickness, flake concentration, polymer medium and coating 17 thickness (Huang, 1987). Theory of Migration of Indirect Food Additives Migration is used to describe the transfer of substances from the package material into the food product. Migration may be either global or specific. Global migration refers to the total transfer of package components into the food.product which may be either toxic or nontoxic. Specific migration relates to a specific individual component which may migrate into the food. These may be of either toxicological interest or used as labelled compounds to determine the extent or mechanism of migration (Crosby, 1981). The migration process depends in part on the diffusivity of the migrant. Diffusivity, or the diffusion coefficient (D), is defined as the tendency of a substance to diffuse through the polymer bulk phase (Giacin, 1980). The concentration gradient is the driving force, where dissolved species diffuse from a region of higher concentration to an area of lower concentration (Giacin, 1980). The rate of diffusion is defined by Fick's first law: an - -DA ds (3) dt dt where m is the mass of component transferred, t is the time, c is the concentration, D is the diffusion constant and A is the area of the plane across which diffusion occurs (Crosby, 1981). The negative diffusion. constant results- as the concentration falls as mass transfer occurs. 18 Fick's second law describes diffusion over an infinite surface area (ie., a sheet): 99 ' D dis: (4) dt dx’ where x is the direction of diffusion. In the second law, D is constant and independent of the concentration. Hence, for steady state diffusion with a fixed concentration gradient, solution of Fick's second law leads to a determination of the concentration as a function of position and time (Crosby, 1981). The effect of temperature on diffusion is described by the Arrhenius equation: . k - A exp -(E/RT) (5) where k is the rate of reaction, A is the frequency factor, E is the energy of activation of the reaction, R is the gas constant, and T is the absolute temperature. The diffusion process is accelerated by increasing temperature. Package systems include 1) nonmigrating: 2) independently migrating; and 3) leaching (Briston and Raton, 1974). In the nonmigrating system, migration takes place from the surface of the packaging material to the product. The diffusion coefficient approaches zero and is not measurable. In the independently migrating system, the diffusion coefficient is measurable under specified time-temperature conditions. Diffusion takes place as the component evaporates from the surface of the polymer and is replaced by similar components l9 diffusing through the bulk phase. The rate of migration and amount transferred depend on the contact phase volume, boundary layer resistances in the extracting phase and the time scale for desorption (Giacin, 1980) . In the third system (leaching) the food penetrates into the plastic which disturbs its physical structure and changes the phase boundary between the food and plastic (Crosby, 1981). This causes the plastic to swell increasingly over time. As a result, the diffusion constant also increases with time. Measurement of Package Material Temperature During Microwaving Migration of volatile compounds is dependent on temperature. Accurate temperature measurement at the surface of the packaging material during microwave heating is essential to correlate the level of migrants released‘with the cooking condition. Maximum use temperature data and migration at that temperature is essential to establish regulations for global and specific migration. A simple technique which utilizes melting point standard waxes (Omega Engineering, Stamford, CT) to determine the temperature attained by plastic materials upon microwave exposure was used by Dixon-Anderson et al. (1988) . The liquid waxes were applied to the plastic material surface using capillary action. The melting temperature of the waxes ranged from 52-107 'C. The waxes were used to determine qualitatively the temperature of the plastic surface. When the waxes were microwaved alone, no melting occurred. --....-—- - a. .»4 ‘u._‘ A u. 20 Therefore, it was assumed that the waxes melted as a result of heat conduction from the plastic. A linear relationship was found between the time of microwave exposure and the temperature of the plastic material. More accurate temperature profiling Can be achieved using optical techniques such as infrared imaging (thermography) and fluoroptic thermometry. An infrared camera is utilized to give a thermal profile or "thermograph" of the entire package surface at a specified time. The thermal profile can be used to demonstrate variability within a microwave oven due to hot and cold spots as well as between microwave ovens. The infrared imaging technique provides information regarding the range of temperatures experienced by the package material or food product. The fluoroptic thermometry technique is based upon the isolation and measurement of the relative intensities of two sharp fluorescent emission lines from a europium-activated phosphor (Wickershiem and Alves, 1982) . The sensor is a phosphor attached to the tip of an optical fiber. A phosphor can be made to emit light when excited by radiation of higher energy or shorter wavelength (Derek and Wickershiem, 1988). The phosphor typically used is a magnesium fluorogermanate activated with tetravalent manganese. When this material is excited by ultraviolet or blue-violet radiation, it fluoresces in deep red. The afterglow has a measurable rate of decay which varies with temperature. This decay is measured 21 electronically to determine the temperature of the phosphor. The optical fiber transmits UV radiation to the phosphor which becomes excited. The red fluorescence is then returned by the same fiber to the instrument for analysis. The sensor is composed of a minute amount of phosphor powder bound to the end of a UV-transmitting fiber. Luxtron corporation has developed a fluoroptic probe system (Model 750) which is widely used and can accomodate up to four probes. The sensors can operate from -200'C (-328’F) to +450“ C (+842’F) (Derek and Wickersheim, 1988) . This is a much wider range than is typically required for food packaging applications. With microwave transparent packaging, the maximum temperature normally achieved by the food product is equivalent to 212° F (100' C), or the boiling point of water. With susceptor packaging, the temperature of the package can reach 500'F (260° C) (Larson, 1988) . This is still within the range of the fluoroptic sensors. Lentz and Crosset (1988) measured the temperature at the interface of the product and susceptor surface using a Luxtron probe system. The products studied included popcorn, pizza and fish fillets. The popcorn bags reached a maximum temperature of 276' C after four minutes at full power exposure. The maximum temperature reached with the fish fillets was 222' C. A major multilab study was completed under the direction of the National Food Processors Organization (Rashtock et a1. , 22 1990) and the Society of Plastic Industries. The purpose of the study was to generate a multi-lab data base for food/susceptor interface temperatures attained during microwave cooking conditions both with and without a liquid food simulant. Ten laboratories representing food processing and packaging companies participated in this study. Testing was conducted using a 700 watt commercial oven. Luxtron Fluoroptic Thermometry systems were used with either MIW or MIH probe. Products tested included a commercial brands of microwave popcorn and frozen microwaveable pizza. Both ferrous and aluminum based susceptors were represented. The probes were positioned in a standardized location on the susceptor surface. "Full cook times" were determined to be 3:17 minutes for an average pop time for the popcorn: and 6:00 minutes for the pizza. When the probe was placed either butted or in parallel contact with the susceptor surface of the popcorn bag the average temperature achieved was 371' F (188‘ C). The susceptor material was fashioned into a tray and a liquid food simulant was deposited into the tray. The average temperature achieved for this test was 404' F (207' C). Temperature measurements were also made on the surface of the microwave pizza product. In half of the runs, a silicone vacuum grease was applied to the probe tip to enhance contact between the probe and the susceptor surface. The average temperature achieved without the silicone vacuum 23 grease treatment was 359' F (182' C). When the silicone vacuum grease was applied to the probe tip, the average temperature was 375' F (191' C). The data indicate that application of vacuum grease enhances heat transfer to the probe. Factors such as susceptor type, oven type, and physical nature of the product or load affected the temperature reached by the susceptor. Analytical Methods for Determining Volatile Migrants from Susceptor Packages In general, two methods are being used to determine desorption of volatiles from package materials during in- package heating. These include static headspace techniques and diffusion trapping techniques (anon., 1990). The static headspace technique is performed by placing a known amount of susceptor board in a glass vial of a specified volume. The vial is placed in the center of a microwave and typically accompanied with a water load which acts as a simulant for a food load. The vial is then microwaved for a time period equivalent to the actual use condition. The sample is then removed from the oven and placed in a hot air oven at a specified temperature. A gastight syringe is also placed in the oven to warm it to the same temperature of the vial. An aliquot of the headspace volume is then withdrawn with the syringe from the vial and injected into the injection port of a FIDIgas chromatograph. Eluate retention times are compared to retention times of known standards for tentative 24 qualitative identification. Mass spectrometry is used to identify unknown compounds. Either external or internal standard curves can be used for quantification. Testing can be performed under ”actual use" conditions in the microwave oven. This method has several disadvantages compared to diffusion trapping. These include decreased sensitivity compared to diffusion trapping, and variability within and between microwave ovens due to nonuniform heating. Condensation of water from the board on the vial wall can lead to partitioning of volatiles. This will cause a decrease in sensitivity. Equilibration temperature of the sample is lower than the temperature achieved during microwaving. Cooling of the sample during equilibration can lead to condensation of the volatiles onto the vial walls. The diffusion trapping procedure is more sensitive than the headspace method. This method employs conventional heating of the sample. A known amount of susceptor is placed in the bottom of a vial of known volume. Conditioned Tenax GCu is placed into a glass tube which is then inserted into the vial and positioned so that it rests on top of the susceptor sample. The vial is then sealed with teflon-lined septum screw caps, and the sample is heated in a hot oil bath for a specified time and temperature. Following heating, the sample is removed and allowed to equilibrate for at least 16 hours at 35' C. After equilibration, the Tenax GC" is loaded into an injection port liner tube from a gas chromatograph. 25 IA plug of glass wool is inserted at both ends of the liner to contain the Tenax. The carrier gas for the gas chromatograph is shut off, and the injection port liner inserted into the injection port of the chromatograph as quickly as possible. The carrier gas flow is then resumed and the gas chromatographic analysis carried out. Either internal or external calibration techniques may be used to quantify the level of migrants. Mass spectrometry is used to identify unknown compounds. Volatile Migration Studies . Volatiles released during microwaving of a plastic co- extruded cup _(polypropylene/Saran'/polypropylene) were determined by Dixon Anderson, et a1. (1988). Approximately two grams of the plastic container was weighed and placed into glass vials of known volume. The vials were suspended above the glass plate in the microwave and microwaved on full power for time periods of 3 to 7 minutes. A gas tight syringe was placed in a hot air oven at 70' C for 30 minutes prior to sampling. Following microwaving of the sample, an aliquot of the headspace was taken from the vial using the heated syringe and injected into the FID gas chromatograph for analysis. Five major peaks were identified using mass spectrometry. The compounds identified were hydrocarbons and butylated hydroxytoluene (BHT) . The compounds were quantitated using an external calibration curve. The quantity of the compounds increased with an increase in microwave heating times. The 26 same compounds were liberated using conventional heating. The authors concluded that the release of volatiles was primarily a near-the-surface phenomenon since the middle layer (PVDC) did not appear to have contributed to the release of volatiles. The FDA is currently studying the release of volatiles from susceptor packaging using a static headspace technique (Hollifield, et al., 1988). In this technique, a specified amount of susceptor sample is placed into a glass vial of known volume and microwaved at full power for 2 minutes. The vial is then equilibrated in a hot air oven at 90°C, with a gas tight syringe. After equilibration, an aliquot of the headspace volume is transferred to the gas chromatograph for analysis. In a separate study by the FDA, a corn oil food simulant was dispensed into a susceptor tray and microwaved on full power for 3 minutes. The presence of the following compounds in the oil phase were identified using mass spectrometryu 2-Furfural, 2-Butoxy-1-ethanol, 2-Furfurol, 2- Methyl-l-Propanol, n-Butanol. Compounds such as furfural and the various alcohols were thought to be components or breakdown products of the paper or adhesive. Booker and Friese (1989) studied the release of volatiles from a susceptor packaging material following conventional and microwave heating using a diffusion trapping procedure and headspace analysis. For the diffusion trapping technique, a known amount of susceptor sample was placed into a clean, 27 glass vial of known volume. A specified amount of conditioned Tenax GC“ was then placed into a 12- x 75-mm glass culture tube. The tube was then placed into the glass vial and positioned so that the tube rested on top of the susceptor sample. The vial was. then sealed and heated both conventionally and in the microwave. For the headspace analysis, the sample was prepared in a similar manner without the Tenax trap. The vial was also heated both conventionally .and in the microwave. Following equilibration, an aliquot of headspace volume was removed and transferred to the gas chromatograph for analysis. When the diffusion trapping procedure was used, the vials were equilibrated at 40’ C for at least sixteen hours. After equilibration the Tenax was loaded into the injection port liner tube of the gas chromatograph for analysis. The Tenax was held in place by plugs of glass wool which were inserted into the ends of the injection port liner tube. The carrier gas was shut off while the liner was inserted into the injection port and then resumed to purge the sample into the gas chromatograph for analysis. Both packed and capillary columns were used. The limit of detectability for this method represented a few nanograms per gram of sample. Booker and Friese (1989) ran a separate test to determine if the irradiation which takes place during microwave heating has an effect on the susceptor sample, which cannot be achieved using conventional heating. The glass vial 28 containing both the susceptor sample and conditioned tenax was placed in the microwave oven and irradiated for 30 seconds. During this time, the vials acted as a heat sink to keep the sample temperature below 120' F (49' C). No volatiles were collected on the tenax*which led the authors to the conclusion that the release of volatiles from the susceptor were due to heat generation by the susceptor. Booker and Friese (1989) described two classes of volatile materials released by the susceptor upon heating, these include: thermally desorbed compounds which are indigenous to the material (residual chemicals from the papermaking process, solvents from adhesives, and contaminants) and. products produced from pyrolysis of the paperboard, coatings, inks, varnishes, etc. In order to distinguish between these two classes of materials, testing must be done at a variety of temperatures. If the amount of the analyte remains fairly constant, it can be assumed that it was indigenous to the material and not a product of pyrolysis. If, however, the amount of the analyte increases with increased temperature it can be assumed that it is a product of pyrolysis. MATERIALS AND METHODS Susceptor Packaging Material The susceptor packaging material was supplied in sheet form (0.61 x 0.91M) by a food company; The susceptor material consists of metallized (aluminum) polyethylene terephthalate (PET), adhesive laminated to paperboard. This company purchases susceptor material from outside sources and did not disclose either the source or the specific composition of the board. The Power Level of the Microwave Oven A Tappan (650 watt, model 56-4994-10, Mansfield, Ohio) microwave oven and anIAmana Radarange (700 watt, model RR1010, Amana Refrigerator, Inc. , Amana, Iowa) was used for all microwave experiments involving headspace analysis. Temperature profiling of the susceptor sample during microwave heating was done using the Tappan (650 watt) microwave oven. Warm-up and calibration of the ovens to determine power output was performed each day before use. A voluntary guideline issued by the International Microwave Power Institute (anon., 1989) was used to determine the power level of the ovens. The ovens were pre-warmed by placing a one liter beaker containing one liter of distilled water in the center of each oven. The ovens were then operated at full power for 10 29 30 minutes. Following heating, the oven cavity was wiped dry to remove water condensation and the door opened to allow the ovens to cool to room temperature. The oven power wattage was then determined. Two one- liter beakers were each filled with one liter of distilled water. A.glass stirring rod was used to stir the water and.was left in one of the beakers. The initial water temperature (° C) was then recorded using a thermometer. The beakers were then placed into the center of the microwave oven with the sides of the beakers in direct contact. The beakers were irradiated at full power for 2 minutes and 2 seconds (2 seconds is allowed to compensate for the magnetron delay). The accuracy of the oven timer was checked using a stopwatch to time the operation. After irradiation, the water in both beakers was stirred and a final temperature reading was taken. The power output of the microwave oven was then determined using the following calculation: P (watts) - 70 x [( t, + t,)/2] (6) where P is the power output of the microwave oven, ta is the temperature of the distilled water in the first beaker, and t, is the temperature of water in the second beaker. The average power output of the Tappan microwave oven was 723 watts. The oven was rated at 650 watts. The average power output of the Amana Radarange microwave oven was 770 watts. The oven was rated at 700 watts. 31 Conditioning the Tenax GC' Tenax GC ' (35-60 mesh) was obtained from Alltech Associates Inc. , Deerfield, Illinois. To condition the Tenax, it was loaded into a 20 M glass column. The column was then connected to the injection port (but not the detector) of a Hewlett Packard Model 5830A gas chromatograph, equipped with a flame ionization detector (FID). The G.C. was temperature programmed to condition the Tenax. The initial temperature was set at 50' C for 30 min.: the temperature was then increased at the rate of 1' C per min. until the final temperature of 240' C was reached. The G.C. was held at 240' C for 10 hours. The injection port temperature was maintained at 175' C. The carrier gas flow rate (helium) through the column was 43 ml/min. After the Tenax was conditioned it was poured into a 40 ml glass vial which was closed with a screw cap and stored at room temperature until needed. Temperature Profile of Susceptor During Heating in an Oil Bath A disc (10 mm in diameter) of the susceptor material was placed in the bottom of a 40 ml glass vial fitted with a Teflon-lined septum cap (Vari-clean vials, Pierce Chemical Company, Rockford, Illinois). A 12- x 75-mm disposable glass culture tube containing approximately 0.03 g of conditioned Tenax GC' was then placed into the tube so that it rested on top of the susceptor disc. The septum cap was pierced and the thermocouple (Type "K' thermocouple with digital read-out, 32 Pocket-Probe Digital'l made by Electronic Development Laboratories, Inc.) was threaded through the opening. The thermocouple was then placed onto the active face of the susceptor disc and the vial closed. The oil was heated to the desired end temperature using a hotplate equipped with a magnetic stirrer. Vials containing the susceptor samples were deposited in the oil bath and heated for five minutes at the following oil bath temperatures: 200' C, 210' C, 220' C, 230° C, and 240° C. A stopwatch was used to time the temperature measurements which were taken every 0.10 minute. This test was performed in triplicate for each of the oil bath temperatures. Temperature Profile of Susceptor During Heating in the Microwave ' A 10- x 65-mm sample of susceptor material was randomly cut from a 0.61 x 0.91M sheet and weighed. This was placed active side up in a 35 ml glass vial. A teflon/silicone septum was punctured using a 22-gauge syringe to allow the Fluoroptic temperature probe to be inserted into the vial. The septum was then placed on the vial and crimped closed. The probe was inserted into the vial so that the tip was in contact with the active side of the susceptor sample. One probe was used for each susceptor sample and.was.placed in the center of the sample. A Luxtron 750 fiber optic temperature measurement system (LuxtronICorp., Mountain‘View, California) equipped with MIW probes was used for all analysis. 33 Temperature profiling of the susceptor material was done in a Tappan (650 watt, model 56-4994-10, Mansfield, Ohio) oven. The vial was placed on its side in the microwave oven with the crimp cap located to the right of the oven with the active side of the susceptor face up. In one study, the vial was placed in the center of the oven, with a 250 ml water load being used as a competitive load. A 500 ml beaker containing 250 ml of distilled water was placed in the center rear of the microwave oven. The sample was then irradiated at full power for 7 minutes. In another study, the susceptor sample was also placed in the center of the oven and irradiated with no water present at full power for 7 minutes. The temperature profiles for each study were done in triplicate. In a further study, the vial was placed in a hot spot located in the rear of the oven to the right of the center. This study was done with a 250 ml water load, and with no water present. The temperature profiles for each study were done in triplicate. The hot spots for both the Tappan microwave oven and the Amana microwave oven were located by placing a susceptor board (33.0 x 36.5 cm) in the oven and irradiating at full power for 5 minutes. The hot spots were easily determined by examining the areas of the susceptor which had turned brown indicating greater heating. Temperature profiles were also constructed for a frozen microwave pizza susceptor tray. The pizza was placed on top 34 of the tray in the center of the oven. Three fluoroptic probes were placed under the pizza for close contact with the susceptor tray. The probes were located in the left front corner, center right side and center rear of the tray.' The pizza tray was irradiated at full power for seven minutes. The temperature profiles were done in triplicate. In a final study, a temperature profile for the susceptor sample used for diffusion trapping was measured. A disc of susceptor material weighing approximately 0.02 g was placed in the bottom of a 40-ml glass vial. A test tube containing approximately 0.03 g of tenax was also placed in the vial. The teflon/silicone septum was pierced to allow a fluoroptic probe to be inserted into the vial. The vial was closed and placed in the hot spot of the oven. The sample was irradiated at full power for seven minutes. There was no water present in the oven. The temperature profile was done in triplicate. Temperature Profile of Susceptor Surface Utilising a Hughes Thermal Video system An 11.4 x 11.4-cm sample of susceptor board was placed in the center of a Litton Generation II microwave ovens (700 watt, model 2238, Litton Microwave Cooking Products, Minneapolis, MN) elevated one inch off the oven floor by a glass dish. The glass from the oven door was removed to prevent infrared interference between the Hughes Probeye infrared temperature camera (Hughes Aircraft Co., Industrial Products Div. , Carlsbad, California) and the test sample. The 35 metal shield was left in the oven door to prevent radiation from escaping. The oven door remained closed during heating. The sample was irradiated on full power for four minutes with the Probeye camera mounted on a tripod aimed downward toward its. surface. The camera produced a video tape of the temperature profile of the sample throughout the heating cycle. Thermal imaging was done with the use of the Hughes Thermal Image Management computer software by freezing the thermal image at the following times: 10 secs., 20 secs., 30 secs., 60 secs., 120 secs., 180 secs., and 240 secs. Two images were profiled, one using water as a competitive load and the other with no competitive load. In the first study, a one liter'glassibeaker'containing one liter of water was placed beside the test sample. This acts as a competitive load in the oven, absorbing some of the energy as would food. The second test was run with no water present. One replication of each study was performed. Static Headspace Technique for Measuring volatiles Released from the Susceptor During Microwaving The static headspace technique (ASTM Committee F-2.3, 1990) was performed both with and without water present in the microwave. This study was done in both the Amana Radarange (700 watt, model RR1010) and the Tappan (650 watt, model 56- 4994-10) ovens. ‘When the water load was used, a 500 ml beaker containing 250 ml of distilled water was placed in the center rear of the microwave oven. Glass beads were placed in the 36 water to prevent super-heating. A 10- x 65-mm sample of the susceptor material was weighed and placed with its active face upward in a 35 ml glass vial. A teflon/silicone septa (conditioned by irradiating at full power for 10 minutes and heating in a vacuum oven under vacuum at 130° C for at least 16 hours) was placed over the vial with the teflon side toward the vial and the vial crimped shut. The vial was then placed in the microwave oven with the crimp cap to the center right of the oven. ‘The sample was then irradiated at full power for five minutes in both ovens. In another study, the sample was irradiated for seven minutes in the Tappan oven both with and without the presence of water. In an additional study, the sample was placed in the hot spot at the rear of the oven to the right of center and irradiated for seven minutes. This study was also performed both with and without water present. Following irradiation, the sample was placed along with a 1-ml gas tight syringe (Alltech, Deerfield, Illinois) into a 90° C hot air oven and allowed to equilibrate for three minutes. After equilibration, the vial and syringe were removed from the oven. The gas tight syringe was filled with 1 ml of air and the air injected into the vial. An aliquot of headspace gas (0.5 ml) was drawn into the syringe and injected back into the vial twice. A one ml sample of the headspace gas was then withdrawn and injected into a Hewlett Packard 5890A gas chromatograph equipped with a flame ionization detector (FID). Each analysis was done in 37 triplicate. The G.C. conditions were as follows: A fused silica capillary column (30M) with an I.D. of 0.32 mm was packed with Supelcowax" 10. To elute the sample, the G.C. was temperature programmed. The initial oven temperature was maintained at 40° C for 5 min.: the temperature was then increased at a rate of 3° C per min. until the final temperature of 165° C was reached. The oven temperature was then maintained at 165°(: for 5 min. The injection port temperature was set at 200'<: and column head pressure was maintained at 0.77 kg/cm’ (11 psi). The helium flow rate through the column was 2.21 ml/min. All injections were accomplished using a splitless injection port. Diffusion Trapping Technique for Measuring the Release of Volatiles from the Susceptor During Conventional Heating A diffusion trapping technique (Booker, 1989) was used to measure the release of volatiles from the susceptor material during conventional heating as shown in Figure 3. A disc of susceptor material (10 mm diameter) was randomly cut from a 0.61 x 0.91M sheet. The disc was weighed and placed in the bottom of a 40 ml glass vial. A 12- x 75-mm disposable glass culture tube containing approximately 0.03 g of conditioned Tenax GC' was placed in the vial so that it rested on top of the susceptor disc. The vial was then closed using a teflon-lined septa and screw cap closure. This was placed in an oil bath which was heated on a hot plate with a magnetic Tenax I 38 Thermometer Susceptor C: / Sample L / :1 Corn Oil J \/ I/fl K / \\- / \HOIPISIO / C Figures. SmenmtIcoIDIIIusion‘l’rqaplnng. 39 stirrer for five minutes. The oil bath temperatures were: 200’ C, 210° C, 220° C, 230° C, and 240° C. Following conventional heating of the sample, the vial was placed in a 50° C hot air oven (Model 18, Precision Scientific Company, Chicago, Illinois) and allowed to equilibrate for at least 16 hours. After equilibration, the Tenax was removed from the glass culture tube and loaded into the injection port liner tube of the gas chromatograph using a glass funnel. The Tenax was held in.place by plugs of glass ‘wool on.both ends of the liner; .A.togg1e switch was installed on the gas chromatograph to shut off the carrier gas flow. During loading, the injection port was quickly opened, the gas flow terminated and the injection port liner containing the Tenax inserted into the injection port. The injection port was then closed and the flow resumed. Gas chromatographic analysis was carried out using a Hewlett Packard 5890 gas chromatograph equipped with a flame ionization detector. The gas chromatographic conditions and temperature program were identical to those described previously for the static headspace analysis of the susceptor heated in the microwave. Three replicates were performed for each of the oil bath temperatures. Headspace Technique for Measuring the Release of Volatiles from the Susceptor During Conventional Heating A 10- x 65-mm sample of susceptor material (same sample size used for headspace analysis in the microwave) was cut in 40 half and placed in a 40 ml glass vial with screw cap. The vial was then closed and placed in an oil bath at a specified temperature for five minutes. The oil bath temperatures were: 200° C, 210° C, 220° C, 230° C, and 240° C. The vial was then removed from the oil bath and equilibrated along with a 5 ml gas Lok syringe in a hot air oven at 90° C for 5 minutes. A one ml aliquot of the headspace gas was removed from the vial with the syringe and injected into the Hewlett Packard 5890 GC(FID) for analysis. The gas chromatographic conditions and temperature program used were the same as those described previously for static headspace analysis. Three replicates were done for each of the oil bath temperatures. Identification and Confirmation of Volatiles using Mass Spectrometry Mass spectrometry was used to confirm the identity of the six major compounds for which standard curves were made. External standards were made up using hexane as the solvent. A headspace technique was used for mass spectrometry. The gas chromatograph which was used had no toggle valve to shut off total flow which prevented mass spectrometry analysis using diffusion trapping. The sample was heated in the microwave for 5 minutes on full power with a 250 ml water load. The concentration of styrene in this sample was too low for mass spectrometer confirmation. Another sample was heated in the microwave for 5 minutes on full power with no water 41 load to confirm the presence of styrene. The sample was then heated along with a 0.5 ml gas tight syringe in a 90° C hot air oven for three minutes. Following equilibration, a 0.5 m1 aliquot of the headspace was injected into the GC/MS for analysis. A 100 ppm standard solution containing both analytes was made using Hexane as a solvent. The standard solution was used to confirm the identity of the six eluants in the headspace sample. The Gas Chromatograph (Delsi Instrument #Di700, Delsi, Inc., Houston, Texas) conditions were as follows: A fused silica capillary column 30M with an I.D. of 0.32 mm was packed with Supelcowax" 10. To elute the sample the G.C. was temperature programmed. The initial oven temperature was set at 45° C. The temperature was immediately increased. upon injection of the sample at a rate of 10°C per min. until the final temperature of 165° C was reached. The Mass Spectrometer (Nermag RIO-10C, Delsi, Inc., Houston, Texas) was a quadropole mass spectrometer operating in the Electron Impact mode. Quantification of Volatiles using External Standard Curves External standard curves were constructed and used to quantify the volatiles released from the susceptor material using both the diffusion trapping and headspace techniques. Liquid standards were made at concentrations ranging from 10 to 500 ppm (v/v) using hexane as a solvent. Both Isopentane and High Pressure Liquid Chromatography (HPLC) grade water 42 were tried initially but gave quite varied results from run to run. A one ul aliquot of each standard solution was injected into the Igas chromatograph for analysisw The conditions were the same as listed previously. The analysis was performed in triplicate. The standard curves were constructed to relate the area response of the analyte to its absolute quantity. RESULTS AND DISCUSSION Oil Bath Time vs. Temperature Correlation Using a "Type R" thermocouple and a stopwatch, a temperature profile of the susceptor sample was determined during heating in an oil bath at specific temperatures (200°C, 210°C, 220°C, 230°C, and 240°C) for five min. After the susceptor sample was heated for approximately 2.8 min., the temperature of the susceptor sample was within a few degrees of its maximum. The average temperatures and standard deviations of the susceptor material during heating are shown in Tables 1-5. The temperature profiles of the susceptor material during heating at each oil bath temperature are shown in Figure 4. Each data point represents three replications during heating at a particular oil bath temperature. Microwaving Time vs. Temperature Correlation A Luxtron 750 fiberoptic temperature measurement system with MIW probes was used to measure the temperature of the susceptor sample centered in the Tappan (model 56-4994-10, 650 watt) microwave oven during heating at full power for seven min. , with and without water. The data represent 3 replications of each condition and are shown in Tables 6 and 7. The maximum average temperature achieved with a water load was l75.9° C (348.7° F) and without water it was 184.1° C 43 44 Table 1. Temperature of Susceptor Material During Heating in a 200°C Oil Bath for five min. Tine_1min.1 Axsl_Sussent9r Stdl_Dexiatien Jammmuauau:1_CLsa. 1:_Cl 0.0 22.0 0.0 0.4 114.7 3.5 0.3 151.7 4.5 1.2 163.7 5.9 1.6 177.3 6.9 2.0 132.7 6.7 2.4 137.0 5.1 2.3 190.0 2.9 3.2 192.0 1.6 3.6 193.7 1.3 4.0 195.3 1.3 4.4 196.7 2.1 4.3 197.7 2.6 5.0 193.3 3.1 Table 2. Temperature of Susceptor Material During Heating in a 210°C Oil Bath for five min. Tine_lnin.1 Axe..§uscentor Std._nexiation Temperature_£L£n. .C_£1 . 0.0 22.0 0.0 0.4 92.0 11.3 0.3 133.0 12.1 1.2 162.7 9.6 1.6 176.0 3.3 2.0 134.7 7.6 2.4 190.0 6.5 2.3 193.3 5.4 3.2 195.7 4.5 3.6 197.0 3.7 4.0 193.3 3.7 4.4 199.0 2.9 4.3 200.7 2.5 5.0 201.7 2.5 45 Table 3. Temperature of Susceptor Material During Heating in a 220° C on Bath for five min. 1139101011 W W WM). 1L2). 0.0 22.0 0.0 0.4 122.0 . 12.7 0.3 164.0 7.4 1.2 134.3 5.0 1.6 195.7 3.9 2.0 203.0 2.9 2.4 203.3 1.9 2.3 212.7 1.7 3.2 215.7 1.7 3.6 213.0 2.5 4.0 219.3 3.3 4.4 220.0 3.6 4.3 220.0 4.6 5.0 219.7 4.5 Table 4. Temperature of Susceptor Material During Heating in a 230° C Oil Bath for five min. mi . W W W .(°_C.). 0.0 22.0 0.0 0.4 122.0 5.4 0.3 176.0 6.4 1.2 200.7 5.3 1.6 214.0 4.1 2.0 221.7 2.9 2.4 226.3 2.9 2.3 229.7 2.9 3.2 232.0 2.9 3.6 232.7 3.3 4.0 233.0 3.6 4.4 233.0 3.7 4.3 233.3 2.9 5.0 233.0 2.5 46 Table 5. Temperature of Susceptor Material During Heating in a 240° C Oil Bath for five min. Magnum .(_9.).° 0.0 22.0 0.0 0.4 113.0 15.6 0.3 176.3 9.6 1.2 203.0 3.6 1.6 213.3 0.9 2.0 227.3 0.9 2.4 233.3 1.7 2.3 237.0 2.5 3.2 239.0 2.9 3.6 240.7 3.1 4.0 241.0 2.3 4.4 241.7 1.7 4.3 241.3 0.9 5.0 241.7 0.9 47 .55 02. .2 0229358. 850QO 8 5am =0 cm 5 9581 95:0 5509.5 .0 2:96. 225350... .5. 059.... »c _ EV 08 _.P n6 o.¢ m.n o.n 9N 9N m; 0.. .020 0.0 —___——~b-—-—p—--h—~_pn—nhnp—th-——pup—ann—n-np °.° CV 08 0|. 8v SN I Q omm I'- CV 08 I Q SN I D 0 0 o (Q) emmJeduJei 48 Table 6. Temperature of Susceptor Material During Heating at Full Power for seven min. in the Center of a Tappan Microwave Oven with a 250 ml water load. Iim2_l51 5291.525222LQI 553003;0_092131190 Tgmpsrgture_£1£n. .C_Ql 0.0 23.3 0.1 20.0 96.3 4.4 40.0 169.7 4.5 60.0 172.0 4.2 30.0 170.3 1.5 100.0 171.0 2.1 120.0 173.1 4.6 140.0 170.3 6.2 160.0 163.3 7.2 130.0 174.4 10.7 200.0 173.0 10.5 220.0 175.3 6.7 240.0 173.0 5.3 260.0 173.1 6.6 230.0 174.1 6.6 300.0 175.5 6.0 320.0 176.0 4.6 340.0 174.5 3.1 360.0 173.3 3.0 330.0 171.9 5.2 400.0 170.5 6.9 420.0 169.7 3.2 49 Table 7. Temperature of Susceptor Material During Heating at Full Power for seven min. in the Center of a Tappan Microwave Oven with no water. 1135.151 A291_§u§§ent2r §Lan§52§.092i5§ien I:mm&uaflau:a.CL£n. 11421 0.0 22.3 0.5 20.0 34.2 2.3 40.0 162.2 4.3 60.0 172.1 5.9 30.0 174.3 5.3 100.0 175.7 4.7 120.0 177.9 5.0 140.0 179.3 5.2 160.0 131.2 5.2 130.0 131.5 4.7 200.0 132.4 4.0 220.0 132.3 3.6 240.0 131.6 3.7 260.0 131.4 4.0 230.0 131.4 4.0 300.0 132.0 5.6 320.0 132.5 6.1 340.0 133.0 6.7 360.0 133.3 7.6 330.0 133.5 3.4 400.0 133.3 3.9 420.0 134.1 9.2 50 (363.4%fi. ‘When water was present it absorbed some of the microwave energy which caused a decrease in the temperature of the susceptor. A similar study was performed by placing the susceptor sample in the hot spot of the Tappan microwave oven and irradiating at full power for seven min. The temperature data shown in Tables 8 and 9 represent three replications. The presence of water causes a decrease in temperature of the susceptor. The maximum average temperature attained with a water load was 179.2°C:(354.6°F3 and without water was 214.l° C (417.4° F). The temperature profile curves for susceptor samples are shown in Figures 5 and 6. The temperature of a frozen microwave pizza susceptor tray placed in the center of a Tappan microwave oven and irradiated at full power for seven min. was measured using fluoroptic probes. three probes were placed beneath the pizza on the susceptor surface (left front corner, center right side, and center rear) to record the susceptor temperature. The temperature 'data are shown in Table 10. The maximum temperature reached by the pizza tray was 423.2“F (217.3° C) after seven min. which was measured by the probe located in the center rearu In the Tappan microwave oven, the hot spots are located along the outer edges of the oven floor. The probe which recorded the maximum temperature was located on a hot spot. The temperature data represents three replications. 51 Table 8. Temperature of Susceptor Material During Heating at Full Power for seven min. in the Hot Spot of a Tappan Microwave oven with a 250 ml water load. Time_l§l. Axgi_§u§952tgr standard_ngxiatien 19099235029_£:n. llJZL 0.0 23.4 0.1 20.0 90.6 0.9 40.0 163.5 2.9 60.0 163.9 9.2 30.0 165.0 1.1 100.0 169.2 9.3 120.0 173.3 7.3 140.0 175.3 5.4 160.0 174.1 3.4 130.0 171.5 2.5 200.0 171.3 1.3 220.0 172.1 2.4 240.0 174.5 3.3 260.0 177.3 3.0 230.0 179.2 2.3 300.0 173.2 4.5 320.0 .176.3 5.6 340.0 173.3 5.0 360.0 170.9 5.1 330.0 169.3 6.1 400.0 163.3 5.9 420.0 166.5 4.0 52 Table 9. Temperature of Susceptor Material During Heating at Full Power for seven min. in the Hot Spot of a Tappan Microwave Oven with no water. Time_l§l 0291.525252t9; Standard_nexiation Ismngratnzg_i_£n. .L_Ql 0.0 22.3 0.3 20.0 115.6 13.9 40.0 176.3 13.3 60.0 197.2 3.4 30.0 193.2 5.0 100.0 197.3 6.5 120.0 197.3 6.9 140.0 193.4 7.4 160.0 199.3 7.5 130.0 200.7 7.6 200.0 202.1 7.7 220.0 203.7 7.3 240.0 205.2 7.5 260.0 206.6 7.7 230.0 210.0 6.6 300.0 209.2 7.7 320.0 210.2 7.9 340.0 211.2 7.9 360.0 212.3 3.0 330.0 213.3 3.2 400.0 213.9 3.6 420.0 214.1 3.3 53 600.. .055 a 505.3 98 55. :05 05320.: 5&8. m .o .0500 05 5 .55 :33 .2 5026.. :5“. .0 9.28: 95.5 .2885 3 052a 05.8350... .m 059“. Amv oEF ONV sagagchfl 9N Own 8. on— ONp On 8 On —.-_.P_.._br_.._.hb.p—.-_..—pb—.._..—-—.._0.0 86.. .86; 0.0 86.. oz 4 4 3.3 (3) aJnlDJdeai 54 000.. .203 0 505.3 000 5.3 :05 0.63952 5000... 0 .0 Sam .0... 05 5 .55 00.60 .0. .0300 =0". .0 05.00... 0550 3.00005 .0 0.00.0 0.30.0050... .0 0.00.“. Amv 0:. .5 out can can Ofln 8n CNN 3N O—N 00— 3— cup cm 8 On 0 _.._5PP..p.._.r_bF—._—..bbPh.._.Lbb._.._..rad 83 .06; 0:0 08.. 62 I °. n N a. 3 O. n h ‘I O. 9 °. °. :9 8 ‘3 8 v- v- v- o- 4; §. UTIUIIITUITIUIIUIIIIIIITIIITIIfiUIITII I O. W N N (3) SJnlDJdeei 55 Table 10. Temperature of Frozen Microwave Pizza Susceptor Tray During Heating at Full Power for seven min. in the Center of a Tappan Microwave Oven. M W W .1... 2... 3... .1... 2... SL.. 0.0 20.3 20.3 20.3 0.0 0.0 0.0 20.0 62.0 59.2 32.4 16.1 24.5 14.6 40.0 115.7 137.6 110.9 39.5 52.3 35.9 60.0 139.2 163.7 139.0 38.9 33.7 27.3 80.0 149.1 170.3 143.0 21.7 20.8 21.8 100.0 160.7 174.0 145.8 13.0 17.0 19.9 120.0 167.5 177.8 149.6 6.5 16.4 17.4 140.0 172.4 180.9 153.5 1.9 16.6 12.9 160.0 176.7 182.9 157.1 2.0 16.3 7.9 180.0 179.8 185.3 160.1 1.5 15.0 4.6 200.0 184.9 186.2 162.0 1.9 14.1 3.2 220.0 186.5 186.3 164.0 1.3 13.6 2.8- 240.0 188.6 187.5 166.3 1.4 13.3 3.7 260.0 191.8 188.9 168.7 3.0 13.1 5.8 280.0 192.7 190.3 171.1 2.9 12.6 7.5 300.0 195.5 192.2 173.3 3.7 12.5 8.5 320.0 197.2 193.9 176.2 1.7 12.8 10.4 340.0 200.0 195.5 178.9 3.2 12.4 11.3 360.0 203.2 198.2 181.0 3.2 11.9 11.6 380.0 207.2 201.3 183.2 2.5 10.8 12.5 400.0 209.4 203.7 185.8 2.0 9.6 13.6 420.0 208.3 204.7 186.6 5.0 9.8 13.0 ° Note. The temperature data represent the temperatures measured by three probes (1 - left front corner: 2 - center rear: 3 - center right side). 56 Some-analytical methods (ASTM F-2 Committee, 1990) suggest placing the vial in the center of the oven to increase the reproduceability for a specific microwave oven. In the Amana (Model RR1010, 700 watt) microwave oven, the hot spot was located in the center. of the oven. When the vial is positioned in the center of this oven, it is subjected to the most intensive heating. In the Tappan oven, the hot spots were located along the outer edges of the oven. The center .of the Tappan oven did.not receive the most intensive heating. A major drawback to analytical test methods which depend on microwave heating is due to the variability in heating within and between microwave ovens. These drawbacks can lead to poor reproduceability between labs, as well as to difficulty in predicting "actual use" conditions seen by the consumer. In another study, the temperatures reached by the susceptor material prepared for diffusion trapping analysis were determined. The weight of each sample was approximately 0.02 g, which is ten times less than was used for headspace analysis. The weight of the sample for diffusion trapping was much smaller, to prevent poor resolution of the chromatograph. The susceptor sample was placed in the hot spot of the Tappan microwave oven and irradiated at full power for seven min. The average maximum susceptor temperature was 135.2‘<: (275.3“ F) . This temperature was much lower than what a susceptor would reach during the cooking of a frozen microwave pizza (Larson, 1988). Diffusion trapping analysis was not 57 performed‘ in the microwave because sufficiently high temperatures could not be reached. The temperatures achieved by the susceptor are shown in Table 11. Hughes Infrared Camera Temperature Profile A Hughes Probeye infrared temperature camera/monitor with Hughes Thermal Image Management computer software was used to record the temperature on the surface of the susceptor sample when irradiated in a Litton Generation 11 microwave oven (700 watt model 2238) for four minutes at full power with and without a water load. The temperatures represent one run and are shown in Table 12. The glass was removed from the oven door to allow the infrared camera to construct a thermal map of the temperatures reached on the susceptor surface at a given time, as shown in Figure 7. The maximum temperature reached on the susceptor surface was 475'F (246.1' C). This temperature was attained with no water present. With a water load present, the maximum temperature attained was 420' F (215.6" C). A profile of the average susceptor surface temperatures both with and without water is shown in Figure 8. Quantification Using xxternal Standard curves Standard calibration curves were constructed for each of the six analytes and are shown in Appendix A. The slope of the curves was found using linear regression. Using the standard curve, the area response units were converted to grams of analyte per gram of susceptor board (see appendix 8) 58 Table 11. Temperature of Susceptor Sample Prepared for Diffusion Trapping During Heating at Full Power for seven min. in the Hot Spot of a Tappan Microwave Oven in the absence of water. Time.1:l Axsl_§nsssntgr afnndarg_nsxiatign 19099141929_1_sn. .L_£l 0.0 24.5 0.3 20.0 55.9 6.9 40.0 95.3 17.9 60.0 103.9 14.7 -30.0 103.5 9.3 100.0 111.7 3.7 120.0 114.9 3.1 140.0 117.4 3.3 160.0 119.2 3.1 130.0 121.4 3.5 200.0 123.0 3.5 220.0 124.4 3.7 240.0 125.3 3.9 260.0 127.2 9.2 230.0 123.7 9.2 300.0 130.3 9.5 320.0 131.5 9.7 340.0 132.9 10.0 360.0 133.5 3.9 330.0 133.4 6.9 400.0 134.3 6.6 420.0 135.2 6.3 Table 10 20 30 60 120 180 240 59 Temperature of Susceptor Material During Heating at Full Power for four min. in a Litton Generation II microwave oven with and without a water load measured using a Hughes Probeye Infrared Temperature Camera. ' 3291.22599259r Max._§nssen:9r 190991319:9_1:sn. 190091310:9_1110. fl§£§I_L930. HQ.L9§0. IKEIEI.LQ§§..HQ.LQ§§ 22.0 22.0 22.0 22.0 171.7 132.2 196.7 232.3 133.3 133.3 201.1 244.4 134.4 191.7 213.3 246.1 132.3 190.6 209.4 245.0 133.3 193.3 214.4 243.3 132.2 196.1 212.2 245.0 215.6 196.7 215.6 244.4 60 54.53555 '31:. 75-8 175.. 275-8 375-9 475-8 . r4 I "rev-Hi z ,' : 4.. , ' ‘ 9"»;5. .. . ’ " 25. s 1 I we: 82:51:13-7 CT= 187-5 £4-38 SUE man-I IET-FKLH as Lat-ID Figure 7. Hughes IR Thermal Map. 61 000.. 0.0.5 0 505.3 0:0 5.3 :05 3030.52 __ 05.0.0000 cos... 0 5 .55 .00. .0. .030... =0“. .0 95.00... 05.00 0.00005 .0 050.0 0.30.0050... 00.5.5 0530... 0050:: .o 0.09.... Am. 0:55 owN CNN SN 00— 8— Ot— ON— 8— 8 OD _._—_._._._._._._._ 003 .30; e..e 003 62 I b .I ONN (3) almoJadwel 62 and to grams of analyte per area of board (see appendix C) for the two static headspace techniques. For the diffusion trapping technique, it was assumed that quantitative transfer of the released analyte occurs. The above calculations are somewhat simplified by omitting the vial volume and injection volume (see appendix D). Volatiles Released During Microwave Heating of the Susceptor and Quantified Using the Static Headspace Technique Six analytes were identified using the gas chromatograph/mass spectrometry technique: 2-methyl-1- propanol, n-butanol, styrene, 2-butoxy-1-ethanol, furfural, and 2-(2-butoxyethoxy)ethanol. These six components had retention times of 6.93, 8.86, 13.48, 20.27, 23.14, 36.38 minutes respectively. The susceptor sample‘was.placed in the center of both the Amana (700 watt) and Tappan (650 watt) microwave ovens and irradiated at full power for five min. The quantity of volatiles detected following heating in both ovens is shown in Tables 13-16. A comparison of the level of volatiles detected in the..Amana. microwave oven 'versus the Tappan microwave oven is shown in a bar graph in Figure 9. The quantity’ of volatiles released is Igreater in ‘the Amana microwave oven. The Amana microwave oven has a hot spot in the center which provides more intense heating. The center of the Tappan microwave oven is not located in a hot spot. In a similar study, the susceptor sample was irradiated at full power for seven min. in the center of the 63 Table 13;” Volatiles Released During Heating of Susceptor Material at Full Power for five min. in the Center of an Amana microwave oven with a 250 ml water WW0 [HIE]: IQ ) (gfidm x :94) (REE. x 19.0) [gtdmz “ :94) load. 005113;: W111. - .4 2 2-methy1- 1-propano1 14.9 57.6 n-butanol 3.3 12.8 styrene 0.0 0.0 2-butoxy- 1-ethanol 0.0 0.0 furfural 0.4 1.5 2-(2-butoxy ethoxy) ethanol 42.4 164.4 * Note. g/g of susceptor material. 17.1 66.5 Table 14. Volatiles Released During Heating of Susceptor Material at Full Power for five min. in the Center of an Amana microwave oven in the absence of water. MW WW 1913.3401119130L340111913’.349.11919n’.34.0.11 2-methyl- 1-propanol n-butanol styrene 2-butoxy- l-ethanol furfural 2-(2-butoxy ethoxy) ethanol * Note. g/g 16.8 14.0 0.7 0.8 28.3 66.8 68.4 57.0 2.7 3.2 43.8 272.1 of susceptor material 33.8 3.7 '11.7 1.4 1.5 23.8 137.9 64 Table 15. Volatiles Released During Heating of Susceptor Material at Full Power for five min. in the Center of a Tappan Microwave Oven with a 250 ml water load. 110310.09 W W MWMW 2-methyl- 1-propanol 8.2 37.3 0.3 1.3 n-butanol 1.2 5.2 0.1 0.3 styrene 0.0 0.0 0.0 0.0 2-butoxy- 1-ethanol 0.0 0.0 0.0 0.0 furfural 0.1 0.3 0.0 0.1 2-(2-butoxy ethoxy) ethanol 6.7 30.2 0.9 4.0 ' Note. g/g susceptor material. Table 16. Volatiles Released During Heating of Susceptor Material at Full Power for five min. in the Center of a Tappan Microwave Oven in the absence of water. fitflfldfilfi.fl£¥1§§1§fl [QCE x 19 l [3100']: 194) (3:9. 1‘ 194] (3100' I: 19.4) 2-methyl- 1-propanol 8.4 36.8 0.9 3.9 n-butanol 2.4 10.5 0.7 3.1 styrene 0.0 0.0 0.0 0.0 2-butoxy- 1-ethanol 0.1 0.4 0.0 0.2 furfural 0.3 - 1.3 0.2 0.7 2-(2-butoxy ethoxy) ethanol 5.9 25.8 0.7 3.0 ' Note. g/g of susceptor material. 65 .505 00.50.55. 90.5 cob 0:05< :0 .0> 595 3030.05 90.... 88 00000... 0 5 .0303 =3“. .0 .55 c0>00 .0. 05.00... 05.00 0:992 638.50 56.. .3899. 8.29.; .6 5.050 .0 050.... 03.0.2 \OQ 09049 4.0 0.0 10.0 N0 33. N m o. \ \. 0.00 0.30 . 4 00 53s 80. 53005 s .202. 02. 0:05.. I . -ON .0? now 10m loop -ONF Iovw fiomw 10m? \_. .05 A ( 9.0 l X amp/6) Amusno 66 Tappan microwave oven both with and without water. The temperature data represent three replications and are shown in Tables 17 and 18. The presence of water provides a competitive load and causes a decrease in the temperature of the sample. The quantity of volatiles released when the susceptor sample was heated with water was lower as would be expected. A comparison of the quantity of volatiles desorbed with a water load versus no load is shown in a bar graph in Figure 10. In another study, the susceptor sample was placed in the hot spot of the Tappan microwave oven and heated at full power for seven min. both with and without water. The temperature data represent three replications and are shown in Tables 19 and 20. The increase in temperature of the sample when it is located in the hot spot causes an increase in the quantity of volatiles which are desorbed. A comparison of the quantity of volatiles released during heating of the sample (no water load) in the center of the oven versus the hot spot is shown in Figure 11. When the glass vial containing the sample is equilibrated in the hot air oven at 90° C the temperature surrounding the vial actually decreases from the temperature it experiences in the microwave oven. This may lead to condensation of some of the volatiles and result in decreased sensitivity. If the sampling is done immediately after microwave heating and is not equilibrated with the syringe, the pre-heated syringe 67 Table 17. Volatiles Released During Heating of Susceptor Material at Full Power for sevenwmin. in the Center of a Tappan microwave oven with a 250 ml water load. 3331399 0331.03309192 fit3n33r3.099139193 (EEK. x 19.4) [5100' x :94] (HIE. x :94) Kazan: x 19.0) 2-methyl- 1-propanol 11.7 50.1 0.6 2.6 n-butanol 3.4 14.3 1.0 4.4 styrene 0.0 0.0 0.0 0.0 2—butoxy- 1-ethanol 0.0 0.0 0.0 0.0 furfural 0.4 1.5 0.1 0.6 2-(2-butoxy ethoxy) ethanol 8.4 35.4 0.9 3.4 ' Note. g/g of susceptor material. Table 18. Volatiles Released During Heating of Susceptor Material at Full Power for seven min. in the Center of a Tappan microwave oven in the absence of water. 3331319 3331.03301111 £93333r3 093139133 . 4 1 4 . 4 4 4 .0391.3.10.1.03331.3.10.1 .3331.x.19.1.01301.x.19;1 2-methyl- 1-propanol 11.8 49.4 0.4 3.0 n-butanol 4.5 13.9 0.5 2.3 styrene 0.0 0.2 0.0 0.0 2-butoxy- furfural 1.0 ' 4.0 0.3 1.4 2-(2-butoxy ethoxy) ethanol 10.4 43.7 0.5 2.3 ' Note. g/g of susceptor material. 68 000.. .0.0>> 0 .0055- 000 5.3 :05 9030.55. .0000 5 0 .0 805.01 0... 5 .0300 =0... .0 .55 c0>00 .0. 05.00... 05.5 000.05. 0.00005 50.. 00000.00 00...0.0> .0 2.5000 .0. 0.00.0 03.000. \OQ m 0.0ka \o «A Q? Q? Q\ 0 S 0 $0 06 8.0". 3.0.0 , 0.8.. 62 u 000.. .203 I (9-0L xzwp/B) .(mueng 69 Table 19. Volatiles Released During Heating of Susceptor Material at Full Power for seven min. in the Hot Spot of a Tappan microwave oven with a 250 ml water load. 3031109 3331423309119 5.1333311091139193 2-methyl- 1-propanol 8.9 37.7 0.3 1.4 n-butanol 1.9 7.9 0.3 1.5 styrene 0.0 0.0 0.0 0.0 2-butoxy- l-ethanol 0.0 0.0 0.0 0.0 furfural 0.2 0.6 _0.1 0.2 2-(2-butoxy ethoxy) ethanol 9.9_ 42.2 0.9 3.9 ' Note. g/g of susceptor material. 70 Table 20. Volatiles Released During Heating of Susceptor Material at Full Power for seven min. in the Hot Spot of a Tappan Microwave oven in the absence of Water. M31309 2-methyl- 1-propanol 10.8 n-butanol 8.9 styrene 0.3 2-butoxy- 1-ethanol 0.0 furfural 6.2 2-(2-butoxy ethoxy) ethanol 10.3 ' Note. g/g of susceptor material. 45.3 37.5 26.1 43.4 0.8 323143331113 51333330099130.1911 [313' x 19-4] ”Ham: x 194) [Ergo x 19.0] (gram: x 19.4] 2.2 71 .5800 on. .m> seem so: 05 E 825“. =3“. 8 .EE 55m to. :30 99.6.9: 5&8. m E 9:81 @550 3:23.: .2385 ES. 3823. mo__.m_o> .o 5530 .: 23E 33.32 .250 N Sam 8: I (9.0L xzwp/B) MRI-1900 72 (90°C) will actually be cooler than the sample. This can lead to condensation in the syringe and also result in decreased sensitivity. The susceptor board may contain as much as 12% moisture (Booker, 1990). When this moisture condenses on the walls of the vial, some of the volatiles may partition with the water. This will also cause a decrease in sensitivity. Volatiles Released from Susceptor Haterial Heated in an 011 Bath using the Diffusion Trapping Technique The six major analytes from the susceptor material which were identified using mass spectrometry (2-methyl-l-propanol, n-butanol, styrene, furfural, 2-butoxy-1-ethanol, 2-(2-butoxyethoxy)ethanol) were measured using the diffusion trapping technique. Using a stopwatch, the samples containing the susceptor material and test tube containing Tenax were heated in an oil bath at specified temperatures (200°C, 210°C, 220°C, 230°C, 240°C) for 5 min. The volatiles which were released from the susceptor material were sorbed by the Tenax trap which was then loaded into the injection port liner of the gas chromatograph for analysis. The injection port liner was then closed and the gas chromatographic analysis performed. The quantity of volatiles released at the various oil bath temperatures is shown in Tables 21-25. The components had retention times which were slightly different than those determined using the static headspace technique. The retention times were 6.55, 8.67, 13.50, 20.24, 23.20, 36.69 min. respectively. A gas chromatograph Table 21. 73 Volatiles Released from Susceptor Material During Heating in an Oil Bath at 200° C for five min. - . Diffusion Trapping Technique. W W (grg- I: IQ") (gram 1‘ 19.4] (REE. x 19.6) [Elfimzli 19.4] 33312323 2-methyl- 1-propanol 32.9 88.7 11.7 31.6 n-butanol 8.9 24.1 4.3 11.6 styrene 0.2 0.6 0.1 0.2 2-butoxy- 1-ethanol 2.7 7.4 0.9 2.3 furfural 3.0 9.0 1.3 4.7 2-(2-butoxy ethoxy) . ethanol 152.7 412.4 10.9 29.4 ' Note. g/g of susceptor material. Table 22. Volatiles Released from Susceptor Material During Heating in an Oil Bath at 210° C for five min. - Diffusion Trapping Technique. Mantis! W EDEJIEE [212.“ :94) (gram: x 194) (HIE. x 19..) (gram: x :94] 2-methyl- _ 1-propanol 24.0 63.8 15.7 41.7 n-butanol 16.1 42.7 9.3 24.8 styrene 0.7 1.9 0.6 1.6 2-butoxy- 1-ethanol 5.4 14.3 2.8 7.6 furfural 13.7 36.6 13.1 34.8 2-(2-butoxy ethoxy) . ethanol 293.7 782.1 74.7 198.8 ' Note. g/g of susceptor material. 74 Table 23. Volatiles Released from Susceptor Material During Heating in an Oil Bath at 220° C for five min. - Diffusion Trapping Technique. W W M (QEQ' x 194] (gram: x IQ“) (Eta. “ 194) Kazan: 1: 19-6) 2-methyl- 1-propanol 29.3 78.2 10.0 26.9 n-butanol 22.3 59.8 10.0 26.7 styrene 0.9 2.3 0.3 0.7 2-butoxy- 1-ethanol 7.3 19.5 2.8 7.6 furfural 19.6 52.3 7.7 20.5 2-(2-butoxy ethoxy) ethanol 358.9 960.0 121.2 324.1 ° Note. g/g of susceptor material Table 24. Volatiles Released from Susceptor Material During Heating in an Oil Bath at 230° C for five min. - Diffusion Trapping Technique. W W anillflfi (gzg- I: :94) (Emil, x 194] (gr: “ 19.4) (Emil: I: :94) 2-methy1- l-propanol 27.2 71.7 10.7 28.1 n-butanol 31.9 84.1 11.6 30.5 styrene 1.9 5.0 0.9 2.3 2-butoxy- 1-ethanol 11.4 30.1 4.8 12.7 furfural 59.5 156.9 28.3 74.5 2-(2-butoxy ethoxy) ethanol 681.6 1797.3 100.7 265.6 ' Note. g/g of susceptor material. 75 Table 25. Volatiles Released from Susceptor Material During Heating in an Oil Bath at 240° C for five min. - Diffusion Trapping Technique. 3881.99383152 Mahdi: (QEQ. x 194) (gram: x :94) (HI: x :94) [gramz IE IQ") 2-methyl— 1-propanol 26.0 n-butanol 35.0 styrene 2.7 2-butoxy- l-ethanol 16.4 furfural 93.7 2-(2-butoxy ethoxy) ethanol 666.8 ' Note. g/g of susceptor 68.0 91.5 7.2 42.8 244.6 1729.3 material. standard_nexiation 5.5 14.3 13.4 35.0 1.0 2.6 7.8 20.5 22.8 59.6 173.8 446.0 76 interfaced with a mass spectrometer would eliminate the identification problem. which occurs due to 'variance in retention times. The differences in retention times between the eluants remained relatively constant however, which enabled the peaks to be identified. Variations in retention times between headspace and diffusion trapping may be attributed in part to the manual introduction of the sample to the gas chromatograph in the diffusion trapping procedure. A graph was constructed to show the relationship between oil bath temperature and the average quantity (g/dm’ x 10") of furfural and styrene (see Figures 12-13) . As shown, at increasing temperatures, the quantity of styrene and furfural present increases. This suggests that these analytes are products of pyrolysis of the susceptor material (Booker and Friese, 1989). velatiles Released from Susceptor Heated in Oil Bath - Static Headspace Technique The concentration of the six analytes were measured using a static headspace method and gas chromatography. The susceptor samples were heated in an oil bath at temperatures of 200°C, 210°C, 220°C, 230°C and 240°C for five min. After equilibration of the sample with the syringe in a hot air oven, an aliquot of headspace was injected into the gas chromatograph for analysis. The quantity of volatiles measured is shown in Tables 26-30. 77 63.58... 9.38.. c2950 9%: 3598.2 .55 o>= .2 8.38258... 5mm .5 «85> .8 3.8: 8.50 888.3. .855... 5 £550 a. 2.5“. A8 3388th 50m :0 ovu mnN and mum ONN m p N 0— SN 8N _ _ _ _ _ _ L _ _ o g 8 8 s 8 (9—3 x ztwp/6) muono In [x ’ llIIIIIIIIIIIIIIIII'IIUIIIIIllFTlllrIlU'lIlll 8 .3. In N N I o m N 78 6:258... 93%.... 5.850 gm: 3536.2 .55 3c to. 8.2anth 58 __o «85> a 2:8: 855 588.2... 2.85 5 £55 .2 8:9... 8V 8388223 fom :0 0% 9H and mu ONN m p N 0— Ba _ _ _ _ _ _ _ _ (9-3 x ztun/6) macho 79 Table 26. Volatiles Released from Susceptor Material During Heating in an Oil Bath at 200° C for five min. - Static Headspace Technique. Magnify.‘ W 2-methy1- l-propanol 11.4 50.6 0.6 3.8 n-butanol 1.1 5.0 0.1 0.3 styrene 0.0 0.0 0.0 0.0 2-butoxy- l-ethanol 0.0 0.0 0.0 0.0 furfural 0.0 0.0 0.0 0.0 2-(2-butoxy ethoxy) ethanol 9.1 40.3 0.3 2.0 ' Note. g/g of susceptor material. Table 27. Volatiles Released from Susceptor Material During Heating in an Oil Bath at 210° C for five min. - Static Headspace Technique. Mann MW 2-methyl- 1-propanol 15.7 70.6 0.3 2.6 n-butanol 2.0 9.2 0.0 0.1 styrene 0.0 0.0 0.0 0.0 2-butoxy- l-ethanol 0.0 0.0 0.0 0.0 furfural 0.3 1.2 0.1 0.2 2-(2-butoxy ethoxy) ethanol 30.5 137.5 4.5 22.6 ' Note. g/g of susceptor material. 80 Table 28. Volatiles Released from Susceptor Material During Heating in an Oil Bath at 220° C for five min. - Static Headspace Technique. W W l I I : . ”4] I ,i 3 19") (”z”- H 19.8] [gzflma x 194] 2-methyl- 1-propanol 15.3 66.4 0.2 0.3 n-butanol 3.5 15.0 0.3 1.1 styrene 0.0 0.0 0.0 0.0 2-butoxy- l-ethanol 0.0 0.0 0.0 0.0 furfural 0.4 1.8 0.3 1.3 2-(2-butoxy ethoxy) ethanol 11.9 51.4 4.6 19.6 ' Note. g/g of susceptor material. Table 29. Volatiles Released from Susceptor Material During Heating in an Oil Bath at 230' C for five min. - Static Headspace Technique. mm mm M31153 Lng_x_1.0_1' " 13AM “ 13M " 132384.194” " 2-methyl- l-propanol 15.9 70.2 1.9 9.4 n-butanol 6.0 26.2 1.1 5.2 styrene 0.1 0.4 0.0 0.1 2-butoxy- 1-ethanol 0.1 0.6 0.1 0.2 furfural 2.4 10.4 0.4 1.9 2-(2-butoxy ethoxy) ethanol 41.3 182.2 10.6 49.4 ' Note. g/g of susceptor material. 81 Table 30. Volatiles Released from Susceptor Material During Heating in an Oil Bath at 240° C for five min. - Static Headspace Technique. W MW ”313:: (HIE. x IQ“) (Elfin? x IQ") (Era. x :94] (gram: x 194] 2-methyl- l-propanol 22.0 n-butanol 9.3 styrene 0.2 2-butoxy- 1-ethanol 0.7 furfural 4.5 2-(2-butoxy ethoxy) ethanol 159.2 ' Note. g/g of susceptor 97.3 41.3 0.7 3.0 20.0 714.2 material. 75.4 13.0 10.5 0.4 82 The retention times of the analytes (2-methyl-1-propanol, n-butanol, styrene, 2-butoxy-1-ethanol, furfural, 2-(2-butoxyethoxy)ethanol) were 6.86, 8.83, 13.48, 20.26, 23.14, 36.39 min., respectively. These retention times were in, close agreement. with those found ‘when the susceptor material was analyzed using the static headspace technique, following heating in the microwave. The static headspace technique and diffusion trapping can be easily compared by heating the respective samples in an oil bath, under identical conditions. Levels of the six analytes measured using the two techniques after heating at 230°C are shown in Figure 15. The differences in the level of furfural measured using the two techniques at each of the five oil bath temperatures is shown in Figure 16. Under the same temperature conditions, the diffusion trapping method is much more sensitive. Mass Spectrometer Identification Mass spectrometry was used to confirm the presence of the six analytes: 2-methyl-1-propanol, n-butanol, styrene,‘ 2-butoxy-1-ethanol, furfural, and 2-(2-butoxyethoxy)ethanol. A. comparison of the 'mass to charge ratio and relative abundance of 3 ions present in the standard solution versus the sample for each of the six analytes shows very good agreement (Table 31). 83 83258... 883mm: 265 .m> ascent. c2350 9.53 3.38.2 SE 95 to. 5mm :0 0 8m 8 s 5528... 55:5 882% 8.25.5 .o 5:35 .3 8598 9232 \00 8Q N . \\\A\ to 8,... Swamp—8: S ascent 55:50 I \ ION CV .58 1cm loo— .45.. .03 low? .03 ‘ M (9.0L xzwp/fi) 4190200 84 $3.203 8388... 88m .9 8.93.... 585:5 gem... 3.5365. .5... 2,... .o. 3.3anth anota> .s 53 __o .3 c. 65.8: 8.50 88%.. .82.... .o 556 .m. .59... .00. 22859....» 58 ..o OVN 0mm CNN OPN OON O _ _ .\\\\. . .p 6.6 x . I Q. .. .. . -3 m 18 m -8 .M. .8. m -8. M. -ccp x 2.5.5.8.. 8333... E .. ”M" w... I 9.5%.... 5.95.0 I \ mévm .3 85 Table 31f" Relative Abundance of Ions Present in Susceptor versus a Standard Solution. 3831233 .JhflL. WW 2-methyl- 43 100.00 100.00 1-propanol 71 0.65 0.74 53 "1.69 1.24 n-butanol 41 100.00 100.00 74 0.41 0.36 53 1.66 1.74 styrene 103 100.00 100.00 78 66.12 61.72 76 18.04 17.62 2-butoxy- 56 100.00 l-ethanol 57 100.00 71 7.81 10.19 75 8.47 7.18 furfural 95 100.00 100.00 67 9.42 7.46 69 3.65 1.75 2-(2-butoxy 44 100.00 ethoxy) 57 100.00 ethanol 72 23.31 22.99 130 6.08 6.26 83W CONCLUSION In the research described herein, comparisons were made between the sensitivity of the diffusion trapping technique and the static headspace technique, the variations within and between microwave ovens due to uneven heating, and the effect of the presence of water on the sample temperature when it is heated in the microwave. The static headspace method is commonly used for testing volatiles. This method is simple and less time consuming than diffusion trapping. Heating of the susceptor sample is done in the microwave oven which many feel more accurately represents "actual use” conditions. The microwave oven, however, has non-uniform heating patterns which result in variability'within an oven, as well as between ovens. The presence of a water load decreases the temperature of the susceptor sample which causes a decrease in the amount of volatiles desorbed. It has been demonstrated that the temperature is also dependent on the size of the susceptor sample. These variations can lead to poor reproduceability of results within and between labs. The diffusion trapping technique is more sensitive than the headspace technique under the same heat treatment. It is somewhat more time consuming due to the need to prepare the samples a day in advance to allow for equilibration. This 86 87 inconveni’ence can be overcome by preparing samples daily. This allows the analyst to have.a continuous supply of samples available. The time required for introduction of the sample to the gas chromatograph is negligible. Diffusion trapping analysis was not done following microwave heating of the susceptor sample due to insufficient temperatures which were attained (296°Ffl. Conventional heating is less variable than heating in a microwave oven. This type of heat source will provide good reproduceability of results between laboratories. Due to its greater sensitivity, diffusion trapping is more quantitative technique to use for analyzing volatiles desorbed from susceptor material during heating. Further work in this area should be done to analyze the origin of analytes. Mass spectrometry and diffusion trapping can be used to analyze individual components of the susceptor material including the board, adhesive, and metallized polyester. Another area to study is to establish a method to correlate results between conventional heating and microwave heating. APPENDICES ”DMZ! I ._8&8.-.-_.s.2-~ 5. 9.8 5.35.8 .2 8.5. a... x 3 5:88 can 68 SN 8w 8. 8. o... o —_b-_—uhb-—b-b—-b-n—_-b—nnnp—nnnp.c - G \\n m. \o Iona .0.. . H o \ - J - no \\ 18.... m \ w \ [Shaw \\. - e I ) I V \\ -820 u x \\ Nona—m \ - O H m o\ Icon. 89 9O APpendix A (ccnt.) .6559: .o. 950 3.83.30 .2 2:9... 8.... x 3 5:83 out 8* nun own man can aha 8N nNN SN a: cop ON. 00— nh on ON a \. \ (00m x my) asuodsaa JOlOalSQ 91 Appendix A (cont.) 28% .2 82.6 8.5.5.8 .2 .59... 81m. x 3 5:88 nun Own. nNn Don nhN 8N ONN 8N mh— Or.— NN— OO— 05 On mu 0 FEEtgggfiEEEflrTo \\ ”T8... \\ . HIS. \ ”loom. \ W8: \ W82 (COOL x nv) esuodsea .10138190 92 Appendix A (cont.) .235”..- —->xo.=m-~ .2950 5.8.3.30 .9 2:91.. an... x 3 5:85 nun Own mun Don nhN 8N mNN 8N nhp 00- GN— 00—. as an mu O EEEEEEEEEFEFS \ - mu \ - w- \ loo. 9 .\ H m. \ - 0 [noon .4 \ n H. . \ . a \ W-Sn d \ - w \ HS. % \\ m ) V \ [8... fl \ H x \ “.58 L. \ .I O . , m 93 Appendix A (cont.) 6.2.2”. .2 62:0 5.35.30 .8 0.30.“. 8:... x 3 5.225 use one nut oat nun can man can aha SN nNN 8N n: on. “N— 8— as on ON a —h~hh—bbuh_nnnb—nbhhh-nbn—b-nb—bhbhb~n-—-pun—unnn—nnnhbbbhE-bn—nn-b_bh:—--——bP-h—-nhb—¥ C \ (00m x nv) esuodsea JOlOSlSG 94 Appendix A (ccnt.) ._82.w§osm..x§m-~..~ .o. 256 5.88.80 .8 .59.. an”. x 3 5:85.... Segnocnenounoonooucoueuowuguspcope—cups— 8 8 0? ON a —-P-—hbb—-b—_-p—bb-ben—Pbbbnbb—bhn—~bb—nb-—_._—bubb-np—bbn—Ppp-Ptbb-pn—bbP—nt (COOL x (W) asuodsea JOlOGlGQ APPENDIX 3 Sample Calculation Used for Converting Area Response Units into Grams of Analyte per Gran of Susceptor Board _l_._¥_x_B_ = S A x P grams of board - Calibration Factor; inverse slope from calibration curve Aliquot Size (1.0 ml) .1 S V - Volume of Vial A R = Area Response of the Sample P = Susceptor Board Sample Size (grams) 95 APPENDIX C Sample Calculation Used for Converting Area Response Units into Grams of Analyte per Area (dm’) of Susceptor Board .1. _X_X_B_ ' S A x D dm’ of board Calibration Factor Volume of Vial - Aliquot Size (1.0 m1) - Area Response from sample ON>