Chapter 11
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Recent Advances in Analytical Methods for Determination of Migrants Henry C. Hollifield,
Roger C. Snyder, Timothy P. McNeal, and Thomas Fazio
Center for Food Safety and Applied Nutrition, Food and Drug Administration, Washington, DC 20204
Within the past several years, new developments in analytical technology have enabled a rapid advance in the laboratory investigation of polymer monomers, oligomers, and adjuvants, as well as the determination of their migration into foods and food-simulating solvents. In some cases, i t is possible to measure low parts per billion levels in the polymer and parts per trillion levels in food simulants. This paper describes some of the newer approaches and applications developed to survey consumer products and to evaluate proposed new materials. Included are discussions of (a) a new cell for assessing migration into simulating liquids, (b) mathematical modeling of migration data and application to selection of a fatty food simulant, (c) a multiresidue approach for determining packaging-derived volatile residues in aqueous foods, and (d) use of combined size-exclusion and high-performance liquid chromatographic residue methods. The d i f f u s i o n of chemicals through polymers and t h e i r migration into foods are phenomena that are of interest to the Food and Drug Administration (FDA) i n i t s regulation of polymeric food-packaging materials. In 1958 Congress amended the Food, Drug, and Cosmetics Act, defining i n d i r e c t additives to foods and requiring their regulation. Since the passage of the 1958 Food Additives Amendment, FDA has required migration studies to provide exposure estimates f o r newly regulated i n d i r e c t additives (1). Within the past several years, new developments i n a n a l y t i c a l technology have enabled important advances i n the laboratory investigation of polymeric monomers, oligomers, and adjuvants and the determination of their migration into foods and food-simulating l i q u i d s (FSL). In some cases, i t i s possible to measure parts per b i l l i o n levels i n the polymer and to determine parts per t r i l l i o n levels i n the food-simulating solvents. Some of the more recent
This chapter not subject to U.S. copyright Published 1988 American Chemical Society
Hotchkiss; Food and Packaging Interactions ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 16, 2018 | https://pubs.acs.org Publication Date: March 9, 1988 | doi: 10.1021/bk-1988-0365.ch011
11.
HOLLIFIELD ET AL.
Advances in Analytical Methods for Migrants
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developments include (a) a new migration c e l l for two-sided extraction of polymeric r e s i n compounds, (b) new fatty food simulants, (c) combined a n a l y t i c a l techniques for trace l e v e l measurements, and (d) multiresidue procedures. This paper discusses some of these advances i n which FDA has actively participated. In 1976, FDA awarded a multiyear contract to Arthur D. L i t t l e to assess the s u i t a b i l i t y of t r a d i t i o n a l food simulants such as water, 3% acetic acid, heptane, and corn o i l (2). That same year the National Bureau of Standards (NBS) entered into an interagency agreement with FDA to investigate the factors c o n t r o l l i n g migration 03). Both of these efforts used radiolabeled additives and/or polymers. From these studies came a number of important r e s u l t s . For example, a new, more e f f i c i e n t two-sided extraction c e l l was developed, mathematical models were used to describe the migration r e s u l t s , and alternative food-simulating solvents were investigated. Evaluation of the New Migration C e l l FDA subsequently followed up these studies with i t s own evaluation of the new c e l l (4·) . A new BASIC computer program was used to f i t the observed migration data to the proposed mathematical model. The c e l l was applied to the study of improved fatty food simulants by using a styrene/polystyrene system. This choice was based on the fact that t y p i c a l residual styrene levels (500-3000 ppm) i n c r y s t a l l i n e polystyrene permit a "cold" (unlabeled) study. Also, the v o l a t i l i t y of styrene i s high enough to be used to evaluate the i n t e g r i t y of the c e l l . The migration c e l l i s i l l u s t r a t e d i n Figure 1. It consists of a 23-mL glass screw-cap v i a l and polymer discs on a rack assembly. The v i a l s are f i l l e d with the desired test solvent and sealed with the Miniert Teflon cap containing a s l i d e valve that permits repeated sampling and resealing. Each v i a l contains a constant number of discs stacked on a wire and separated by 3-mm glass beads. For 14 polystyrene discs i n 22 mL of food-simulating solvent, the volume-to-surface r a t i o can be accurately determined (0.73 mL/sq. cm i n our studies). Assembled c e l l s are held i n darkness at the desired test temperature i n a water bath. The water bath provides mild agitation of the c e l l at the rate of 60 cpm with a stroke of 4 cm. Polystyrene discs for migration studies are prepared by pressing polystyrene p e l l e t s i n a template at 400°F (204°C) under a 15,000 p s i force for 30 s. The resultant c i r c u l a r discs are of constant diameter, thickness, and weight. They are characterized by size-exclusion chromatography (SEC), and the residual styrene monomer l e v e l i s determined by high-performance l i q u i d chromatography (HPLC). A small hole i s d r i l l e d i n the center of each disc so that the discs may be stacked on the wire support. Reproducibility of data generated by this technique was evaluated by preparing six i d e n t i c a l migration c e l l s , with water at 40°C as the contact solvent. The solvent i n each c e l l was p e r i o d i c a l l y analyzed for styrene concentration over a period of 2 months. The o v e r a l l r e l a t i v e standard deviation for these determinations was ±2%, indicating the excellent repeatability obtainable by t h i s migration c e l l technique.
Hotchkiss; Food and Packaging Interactions ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 16, 2018 | https://pubs.acs.org Publication Date: March 9, 1988 | doi: 10.1021/bk-1988-0365.ch011
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FOOD AND PACKAGING INTERACTIONS
Styrene migration into the FSL was monitored by reversed-phase HPLC. A 5-ym Cg Zorbax column interfaced with a fixed wavelength (254 nm) UV detector was employed. A mobile phase of 75% a c e t o n i t r i l e i n water at a flow rate of 1 mL/min proved adequate to separate styrene from a l l interferences. Analysis of a l l the various solvent systems on the same column was possible by use of a Brownlee loop column, which consisted of a 3.7-cm long cartridge packed with 10-ym Cg reversed-phase packing material. The loop column i s mounted i n the injector valve where a fixed volume injector loop would normally be located. Since the loop column retains o i l y sample components and allows materials of lower molecular weight to pass through f i r s t , i t permits direct i n j e c t i o n of o i l y as well as aqueous FSL. Oily materials are removed from the loop column between sample injections by flushing the loop column with tetrahydrofuran. Styrene migration from polystyrene discs into the following solvents was monitored at 40°C: water; 8, 20, 50, and 100% ethanol; HB-307 (synthetic t r i g l y c e r i d e ) ; corn o i l ; heptane; hexadecane; decanol; and 3% acetic acid. The migration c e l l s were p e r i o d i c a l l y sampled (25 yL), and the concentration of styrene was determined by external c a l i b r a t i o n . The l i m i t of quantitation of the procedure i s 10 yg styrene/L. Styrene migration, expressed as yg/sq. cm vs. square root of time (s), into a variety of solvents at 40°C i s shown i n Figure 2. This figure shows that at 40°C, styrene migrated at similar rates into 20% ethanol, corn o i l , and HB-307. Figure 2 reveals that varying the ethanol concentration from 0 to 50% i n water caused the rate of styrene migration to vary over one order of magnitude. Ethanol-water mixtures, therefore, would seem well suited as low temperature f a t t y food simulants for a wide variety of foods. Mathematical Modeling Data obtained from migration studies can be interpreted i n terms of simplified mathematical models developed j o i n t l y by NBS and Arthur D. L i t t l e . For example, by f i t t i n g the data generated i n the above study to the migration models, several observations can be made about this styrene-polystyrene system. For short periods of time (
