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Note 101: Identification of Contaminants in Powdered Foods by Direct Extraction Thermal Desorption GC/MS

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Ronald E. Shomo, II, Christopher Baker, and John J. Manura
Scientific Instrument Services
1027 Old York Road, Ringoes, NJ 08551
(presented at Pittcon 2016)

Introduction

The ability to identify volatile and semi-volatile contaminants present in food products without the use of solvent extractions has several advantages including improving sample throughput, reducing the chance of a volatile component being “lost” in the extraction process and eliminating the need for solvent disposal. This study utilizes the advantages of direct thermal extraction GC/MS to identify contaminants in powdered food products. Direct Thermal Extraction GC/MS provides for fast analysis with no carryover problems that can be associated with other GC/MS techniques.

Material and Methods

Samples of powdered foods included the following items:
  1. Coffee Creamer - Non-Dairy
  2. Coconut Flour (organic)
  3. Kids drink mix (tropical punch)
  4. Kids drink mix (lemonade)
  5. Corn Meal
  6. Ice tea mix (artificial sweetener)
  7. Baby oatmeal cereal
  8. Instant mashed potatoes

Desorption tubes (4 mm ID x 4” stainless steel Silco coated) were packed with a small plug of deactivated glass wool and conditioned for 4 hours at 320 C with 20 mL/min of pure nitrogen flowing through the tubes. The conditioning oven was an SIS design and had a 24 tube capacity. The samples analyzed were placed in these pre-conditioned tubes (5-50 mg) and a second plug of glass wool placed to contain the powder. The loaded desorption tube was placed in a SIS model TD5 Thermal Desorption system. (Figure 1), and a 35 mm preconditioned desorption needle was attached.

The TD5 was attached to an Agilent 5973 GC/MS coupled to a 6890 GC. The GC had a SIS cryotrap installed using liquid CO2 as the cryogen. The injector was cooled to -45 C during the desorption process. The TD5 desorbed the samples at 150 C for 5 minutes after a 1 minute non-heated purge to remove any residual oxygen present in the desorption tube. During the desorption process a divert valve is actuated by the desorption software and allows the injection port helium flow to pass through the desorption tube and attached needle into the injection port. After the desorption process is complete the diverter valve switches the flow of helium again to allow the normal injector flow to resume. (See Figure 2)

During desorption the cryotrap remained at -45 C, and after the 5 minute desorption period the cryotrap is ballistically heated to 250 C for 3 minutes and the GC/MS data acquisition is initiated. The MSD was scanning a mass range of 35-450 with a 1 second scan rate.

The GC column used was an SGE BP5MS 0.25 mm id x 15 m with a 0.25 um film. The column had a 5 m silguard 0.32 mm guard column on the front end. The GC operated in the split mode with a 5:1 split ratio. All desorption parameters were controlled by the TD5 software that is integrated into Agilent Chemstation program. Mass spectral data was compared against the NIST14 library software for component identification.

A blank TD tube was run between each sample to verify that no cross contamination or carry over had occurred.

Results and Discussions

Sample #1 was a store brand non-dairy creamer. The packaging was a HDPE plastic bottle. There were both dioctyl and diethyl phthalate present in the product. Phthaltes are plasticiers commonly found in the plastic packaging or introduced in the manufacturing process.1,2 Tris(dimethyldithiocarbamato)iron a common fungicide was also found in less than 1 ppm quantities. The Fungicide is commonly used on corn. The major component of this creamer was corn syrup3.

Sample #2 was a coconut flour. The coconut flour was packaged in a polyethylene bag. This was advertised as an organic product with no additives or preservatives. Unfortunately, this sample was laced with BHT (a common preservative)4 as well as a number of compounds associated with plasticizers including the following, styrene, N-butylsulfonamide, diethyl phthalate, dioctyl phthalate, and butyl undecyl ester phthalic acid1,2. Figure 3 shows a typical chromatogram of the powdered foods after direct extraction TD/GC/MS.

Sample #3 was a kids drink tropical punch flavor, packaged in a foil pouch. The sample contained ethyl acetate and diethyl phthalate.

Sample #4 was a kids drink lemon flavor, packaged in a foil pouch. The sample contained phenol, BHT, and diethyl phthalate.

Sample #5 was corn meal. The product was packaged in a polyethylene bag. No preservatives were listed on the packaging but BHT was clearly present. There was also dioctyl and diethyl phthalates present.

Sample #6 was an ice tea drink packaged in a hard polypropylene container. The sample containedmethyl methacrylate, BHT (not indicated on the package) and diethyl and dioctyl phthalate. Methyl methacrylate is a precursor to forming plastics4.

Sample #7 was an infant oatmeal cereal mix. The product container was a HDPE box. The oatmeal contained approximately 10 ppm of BHT (not listed on the label) and dioctyl and diethyl phthalate compounds. Also found was a trace level (1 ppm) of N-butyl benzensulfonamide, a common precursor used in the manufacturing of plastics1.

Sample #8 was instant mashed potato flakes. Product contained BHT even though this particular preservative is not listed on the package label. Even though the packaging was an aluminum foil bag, there were dioctyl and diethyl Phthalate plasticizers present.

Conclusion

Direct thermal extraction GC/MS is a quick way to identify contaminates in food products without the use of solvents. Each sample has its own unique transfer line (desorption needle), and this eliminates the problem of carry over or cross contamination that is frequently present in other GC/MS methods.

As the data indicates, not one of the tested samples were free from “contaminates”. All of the samples contained some level of plasticizer contamination. Plasticizers most likely originated from the product packaging, but several samples were wrapped in a protective aluminum foil, so the origin of the plasticizers was unknown. There is a growing health concern surrounding the exposure to plasticizers and according to the CDC our diet is the main source of plasticizer intake for humans5.

There is also concerns about the preservative BHT. Japan and several other countries have banned the use of this anti-oxidant.6 In 6 out of 8 samples we tested the preservative BHT was detected even though the label did not indicate this anti-oxidant was used.

References

1. David F. Cadogan and Christopher J. Howick, “Plasticizers” in Ullmann’s Encyclopedia of Industrial Chemistry 2000, Wiley-VCH, Weinheim, doi 10.1002/14356007.a20_439

2. Malveda, Michael P (July 2015) “Chemical Economics Handbook Report on Plasticizers”

3. Yehye, Wageeh A.; Rahman, Noorsaadah Abdul; Ariffin, Azhar; Abd Hamid, Sharifah Bee; Alhadi, Abeer A.; Kadir, Farkaad A.; Yaeghoobi, Marzieh (2015). "Understanding the chemistry behind the antioxidant activities of butylated hydroxytoluene (BHT): A review". European Journal of Medicinal Chemistry 101: 295–312. doi:10.1016/j.ejmech.2015.06.026. PMID 26150290

4. Polymethyl acrylate and polyethyl acrylate, Encyclopædia Britannica. Encyclopedia Britannica. Retrieved 2012-05-09.

5. Third National Report on Human Exposure to Environmental Chemicals, (PDF) U.S. CDC, July 2005. Archived April 1, 2007 at the Wayback Machine

6. James Hamblin (11 February 2015). "The Food Babe: Enemy of Chemicals". The Atlantic. Retrieved 12 September 2015.