The potential toxicity and persistence of perfluorinated compounds in organisms can lead to diseases such as liver cancer, pancreas cancer, and even testicular cancer in animals. Due to their stable physicochemical properties, perfluorinated compounds are unlikely to degrade in the organisms, resulting in high bioaccumulation.

Perfluorochemicals can enter our foods unwittingly through packaging materials, packaging bags, and food contact materials such as various types of coatings, which pose a serious threat to consumers' health. Therefore, the establishment of analytical techniques and methods for the detection of perfluorinated compounds in food contact materials can effectively control and gradually eliminate the contamination of perfluorinated compounds. It is not only conducive to the development of new analytical techniques, but also to the protection of the consumers’ health. On January 4, 2016, the US FDA banned the use of perfluorinated compounds such as mono (di)perfluoroalkyl phosphate diethanolamine salts, valeric acid-4,4-bis-derivative-diethanolamine compounds and phosphonic acid perfluoroalkyl substitutes in food contact materials in the 21 CFR.

Sample Preparation:
Sample preparation is critical to the sensitivity of the test method and the accuracy of the test results. Sample preparation mainly includes two steps: sample extraction and purification. Due to the low content of perfluorinated compounds in food contact materials, their detection mainly focuses on the two aspects of extraction and effective enrichment. At present, the pretreatment methods commonly used for perfluorinated compounds mainly include ultrasonic extraction, solid phase extraction, soxhlet extraction and accelerated solvent extraction, etc.

Ultrasonic Extraction:

Ultrasonic extraction technology refers to the use of mechanical damage of ultrasonic wave and cavitation to accelerate the solvent molecules, thereby improving the solvent penetration ability, which can greatly enhance the extraction efficiency of perfluorinated compounds in the sample. In the study of perfluorinated compounds in paper food contact materials, Begley et al. found that when they used ultrasonic extraction technology, in which ethanol/water (1:1, v/v) was used as the extraction solvent, the samples were ultrasonically extracted in 1h. The recovery rate of perfluorochemicals is 60% to 75%. Compared with those of liquid-liquid extraction, both extraction efficiency and the recovery rate are greatly improved.

Soxhlet Extraction:

The soxhlet extraction is implemented in a solvent reflux state, thus the perfluoro compound in the sample can be sufficiently eluted, showing high extraction efficiency.

Jiang et al. used the soxhlet extraction method to pre-treat the sample and test the perfluorinated compound in the non-stick coating. The results show that when the pH at extraction goes between 9 and 10, a tiny amount of perfluorinated compounds in the sample can be effectively extracted by the reflux method, and the recoveries of the spiked samples can reach 86%~110%. Therefore, this method is more suitable for samples with less perfluorinated compounds than other extraction methods. It has higher extraction efficiency and less sample loss.

Accelerated Solvent Extraction:

Accelerated solvent extraction uses conventional solvents at elevated temperatures (50 to 200 °C) and pressures (1000 to 3000 psi) to increase extraction efficiency by increasing temperature and pressure. Larsen et al. optimized the extraction method of perfluorinated compounds in Fulong, and studied the effects of five different solvents (methanol, water, acetonitrile, ethanol, and chloroform) on accelerated solvent extraction. It was found that methanol accelerated solvent extraction was better than other solvents.

Detection Methods:
The detection techniques of perfluorinated compounds mainly include gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry, such as high pressure liquid chromatography-mass spectrometry and ultrahigh pressure liquid chromatography-mass spectrometry.

Gas Chromatography-Mass Spectrometry (GC-MS):

GC-MS is used to detect perfluorinated compounds in food contact materials. Betula et al. and Lv et al. used different derivatization methods to detect PFOA in coating materials by using GC-MS. It was found that GC-MS is particularly suitable for the detection of PFOA, and the stability and recovery of the method are ideal (the recovery rate is high). Wang et al. established a gas chromatography-mass spectrometry method for the determination of ammonium perfluorooctanoate in some food contact materials. The average recovery rate went as high as 95%~104%, and the detection limit was 1.0μg/L. The method comes with a good recovery rate. GC-MS is less affected by matrix effects when used to detect perfluorinated compounds in food contact materials. Hence, the results are more reliable.

Liquid Chromatography-mass Spectrometry (LC-MS):

Liquid chromatography-mass spectrometry (LC-MS) is currently the most commonly used method for the detection of perfluorinated compounds in food contact materials. It can quantitatively detect perfluorinated compounds in the matrix. Its main advantages are high sensitivity and selectivity, as well as low detection limit, and the sample does not require complex pre-treatment and pre-column derivatization to detect PFOA and PFOS, and LC-MS is more sensitive than GC-MS. Tseng et al. used high pressure liquid chromatography-ion cesium mass spectrometry to measure perfluorinated compounds in food contact materials with a detection limit of 67 ng/L. Comparing with GC-MS, it has lower detection limit, indicating high sensitivity.

Chen et al. reported the detection technique for the detection of PFOS in food packaging materials by UPLC-MS. The method showed that the PFOS was linear in the range of 0.0002~0.1 μg/mL (R2=0.998), and the recovery was 93.8%~101%. Zhang et al. established a method for the determination of PFOA in food paper containers by UPLC-MS by combining accelerated solvent extraction. In this method, PFOA has good linearity (R2=0.9993) in the range of 0.5~50 ng/mL. Their experimental results show that UPLC-MS used to detect perfluorochemicals in food contact materials has many advantages, such as high sensitivity and selectivity, and low detection limit, and the sample does not require complex pretreatment.

References
Jiang HN, Sun MX, Chen ZH, et al. (2007) ‘Micro-Quantitative Characterization of Pentadecafluorooctanoic Acid with GC/MS in SIM Mode’. J Fudan Univ (Nature Sci),46: 291–296.

Jiang H, Sheng X, Yang YY, et al. (2007) ‘Analysis Research Development of PFOS’. Anhui Chem, Ind, 33(2): 5–9.

Wang LB, Zhao Q, Li ZK, et al. (2008) ‘Study on Toxicology of Ammonium Perfluorooctanoate in Food Packaging Materials’. Food Sci, 29(10): 586–592.

Hu WY, Jones PD, Celius T. (2005) ‘Identification of genes responsive to PFOS using gene expression profiling’. Environ Tox Pharm, 19(1): 57–70.

Yang JL, Xie JJ. (2008) ‘Dual Impacts of PFOS on our Textile Trade and Countermeasures’. Int Eco Trade Res, 12: 51–55.

Miao L, Mo JJL, Gan NJ. (2011) ‘Study on Testing of Perfluoroocatane Sulfonate(PFOS) and Perfluorooctanoic Acid(PFOA) in Packaging Material for Food’. Mod Food Sci Tech,27(1): 101–105.

Lv G, Wang LB, Li SC, et al. (2009) ‘Determination of perfluorinated compounds in packaging materials and textiles using pressurized liquid extraction with gas chromatography-mass spectrometry’. Anal Sci, 25: 425–429.

Zhang Y, Pang K, Lv P, et al. (2012) ‘Determination of Perfluorooctanoic Acid(PFOA) in Paper Food Containers by High Performance Liquid Chromatography-Tandem Mass Spectrometry’. Food Sci, 33(22): 207–209.