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Note 21: Detection and Identification Of Volatile and Semi-Volatile Organics In Synthetic Polymers Used In Food and Pharmaceutical Packaging

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By John J. Manura

Presented at the 1994 ASMS Meeting, Chicago, IL

IINTRODUCTION

Synthetic materials including Silicone, Viton® and Buna-N are commonly used in the manufacture of O-Rings and other package sealing materials in the food and pharmaceutical industries for the packaging of products, which are destined for human consumption. The packaged and sealed manufactured products can be exposed to a wide variety of environmental conditions during processing, shipping and storage. As a result, the volatile emissions from these synthetic materials can migrate into the finished consumer product. The food and pharmaceutical industries are concerned about the degree of contamination of their finished products. The following method was developed to detect, identify and quantify the volatile emissions from a wide variety of packaging materials. The method involves the technique called Direct Thermal Extraction which uses a thermal desorption system to thermally extract organics directly from solid matrix materials without the use of solvent extraction or any other sample preparation. The result is a method which is quick, accurate, prevents contamination of samples with foreign solvents and permits the detection of volatiles which would be lost due to evaporation in standard extraction techniques.

Experimental

Solid polymer samples (between 1 and 500 milligrams) was placed into an inert thermal desorption tube on top of a glass wool plug (Figure #1). The sample tubes were then attached to the thermal desorption system and a syringe needle attached. The sample tube was then injected into the GC and the volatiles and semi-volatiles are thermally extracted at various temperatures (between 50 and 250 degrees C) into the GC injection port. The extracted organics were subsequently cryo-trapped at the front of the GC injection port using the GC Cryo-Trap at a temperature of -70 degrees C. After the 5.0 minute thermal extraction was complete, the Cryo-Trap was heated to 220 degrees C to elute the volatiles and begin the GC analysis and identification via the mass spectrometer. The GC (H.P. 5890, Series II with EPC) was maintained at 30 degrees C during the desorption process and then temperature programmed to 260 degrees C at 8 degrees C per minute. The H.P. (Model 5989A) mass spectrometer was used in the EI mode and was scanned from 40 to 800 daltons. The GC peaks were identified from the Wiley NBS library.

For the quantification of the BHT in the cereal and Pharmaceutical products, the method outlined in a previous publication was utilized. (1)

Figure 1

Figure 1 - Short Path Thermal Desorption System

Results And Discussion

In Figure #2, 5 to 10 milligram samples of silicone O-Rings were thermally desorbed at different temperatures in order to study the volatile emissions as a function of temperature. Even at temperatures down to 100 degrees C, a large number of volatile organics were detected from the silicone polymer. Optimum results were obtained at a thermal desorption temperature of 130 degrees C. The major peaks (Figure #3) in the Silicone O-Ring were identified as the cyclo-Siloxane series of compounds which originated from the silicone polymer. The major peaks at masses 207, 281, 267 and 355 are commonly seen in normal GC background. These GC background peaks originate from the silicone septa used in the GC injection port. The higher thermal desorption temperatures (170 degrees C and higher) produced some polymer decomposition as well as the appearance of even higher molecular weight siloxanes. The Direct Thermal Extraction technique is much more efficient than solvent extraction techniques (Figure #4). The thermal extraction process is more efficient at extracting the siloxanes due to the limited solubility of the siloxanes in solvents. In addition, the lighter volatiles would most likely be lost due to evaporation in the solvent reduction steps in standard solvent extraction techniques.

Figure 2

Figure 2 - Direct Thermal Extraction of Silicone O-Rings at Different Temperatures

Figure 3

Figure 3 - Direct Thermal Extraction Of Silicone O-Rings At 130 degrees C


Figure 4 Silicone O-Ring - Direct Thermal Extraction vs Solvent Extraction (ppm)
                            Direct Thermal      Solvent 
Compound                     Extraction        Extraction
---------------------      -------------      ------------        Polysiloxanes                    800               75
2-Butoxyethanol                    7                -
2-Methoxyethoxyethanol             8                -
Acetaphenone                       7                -
2,5-Dichlorophenol                 6                -
1,2-Benzoisothiazole               4                -
2,4-Dichlorobenzaldehyde           6                -
Dimethylstyrene                   14                1
Di-t-butylmethoxyphenol           23                1
2,4-Dichlorobenzoic Acid          42                9
Tetrachlorobiphenyls               4                4
Diethylphthalate                   6                1
Dibutylphthalate                   6                1
Di-2-ethylhexylphthalate           7               12

In a likewise manner, 4 to 10 milligram samples of a Viton® O-Ring were analyzed via the Direct Thermal Extraction Technique (Figure #5). Optimum analysis of the Viton® O-Ring was achieved at a thermal extraction temperature of 150 degrees C. The anti-oxidants BHT and BHA were two of the major components in the Viton® polymer, in addition to a number of alcohols, aldehydes and hydrocarbons (Figure #6). A Buna-N O-Ring was analyzed as shown in Figure #7. This sample was thermally desorbed at 150 degrees C. Again the anti-oxidants BHT and BHA were present. Most of the compounds detected were identified as hydrocarbons.

Figure 5

Figure 5 - Direct Thermal Extraction of Viton® O-Rings At Different Temperatures

Figure 6

Figure 6 - Direct Thermal Extraction Of Viton® O-Rings At 150 Degrees C

Figure 7

Figure 7 - Direct Thermal Extraction of BUNA-N O-Rings At 150 degrees C

The analysis of a plastic food wrap is demonstrated in Figure #8. For this analysis, a 3 square inch piece of the plastic food wrap was inserted into the thermal desorption tube. The sample was thermally extracted at 100 degrees C. The major compound detected was BHT. BHT serves a dual purpose in the plastic food wrap as an anti-oxidant and also as a food preservative. BHT is extremely volatile and can easily migrate from the plastic food wrap into the food product, especially if it is used in applications as the microwave cooking of foods.

Figure 8

Figure 8 - Analysis Of 3 sq. in. dia. Plastic Food Wrap By Direct Thermal Extraction

A demonstration of the migration of BHT into a food product is shown in Figure #9. For this study, deuterated BHT was used as an internal standard for the quantification of the BHT (1). One hundred milligrams of the corn-based cereal was placed into the thermal desorption tube and 100 nanograms of deuterated BHT internal standard were added. This cereal food product contained no BHT during manufacture. However, BHT was used to coat the inside of the plastic pouch containing the cereal. As can be seen, the BHT easily migrated into the cereal product from the packaging container. BHT was quantified at a level of 11.3 ppm in this corn-based cereal product. In a likewise manner, BHT has been quantitated in other cereal products, dried potatoes, meat products and potato chips.

Figure 9

Figure 9 - Quantification Of BHT In Cereal (100 mg)

An example of the migration of BHT into a pharmaceutical product is shown in Figure #10. The Penicillin tablet originally contained no BHT during manufacture. However, the tablets analyzed were packaged by a local drug store into a styrene plastic bottle. Again deuterated BHT as well as deuterated Naphthalene were added as internal standards to 50 milligrams of the sample in order to quantify the BHT in the pharmaceutical product. In this sample, 3.5 ppm of BHT was detected and quantified. In addition, Butyl Acetate and N-Butyl Benzenesulfonamide were detected which may have originated from the packaging material.

Figure 10

Figure 10 - Quantification Of BHT In Pharmaeceutical Product (50mg)

Conclusion

The Direct Thermal Extraction technique used in conjunction with the Short Path Thermal Desorption System was used to demonstrate the advantages of this method for the detection, identification and quantification of volatile emissions from packaging materials and their subsequent migration into finished food and pharmaceutical products. The method is quick and accurate and far superior to solvent extraction methods. There is no contamination due to impure solvents and the loss of volatiles in sample extraction and concentration is eliminated, since no sample extraction or other sample preparation is required. Quantification of volatiles produced results with relative standard deviation of less than 5%. This technique can be easily adapted for a standard quality control method for the monitoring and control of volatile emissions from packaging materials as well as the migration of these volatiles into the finished manufactured product.

Reference

1. Manura, John, LC/GC, Vol. 11, No. 2, (2/93) Pp. 140-146.,

2. Presented at ASMS May, 1994.

Viton® is a registered trademark of DuPont Dow Elastomers