Comparison of room temperature and cryogenic sample processing in the analysis of chemical contaminants in foods

Authors: HAN, LIJUN - China Agricultural University; Lehotay, Steven; Sapozhnikova, Yelena

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/14/2017
Publication Date: 11/14/2017
Citation: Han, L., Lehotay, S.J., Sapozhnikova, Y.V. 2017. Comparison of room temperature and cryogenic sample processing in the analysis of chemical contaminants in foods. Journal of Agricultural and Food Chemistry. 66:4986-4996. https://doi.org/10.1021/acs.jafc.7b04359.
DOI: https://doi.org/10.1021/acs.jafc.7b04359

Interpretive Summary: Analysis of pesticide residues and environmental contaminants in diverse food types is an important application for improved food safety and environmental health. Recent progress in streamlining and automating sample preparation, analytical separations, detection, and data processing have led to much faster sample throughput in routine monitoring of contaminants in food. However, sample processing remains as the rate limiting step in the overall analytical procedures, and faster approaches are needed to address this weak link in the chain. In this study, different methods of sample processing were compared in the analysis of chemical residues in a mixed food matrix, and results showed that use of a specialized liquid nitrogen cryomill device gave the best results, but not so much better than a faster and easier method at room temperature using standard equipment. The latter approach achieved acceptable results to allow start-to-finish analysis and reporting of residues in a batch of 20 perishable food products within the same working day. This finding means that labs can use the simpler, faster, and cheaper approach to sample processing when monitoring chemical residues in food.

Technical Abstract: In this study, analytical results were compared when using different approaches to bulk food sample comminution, consisting of a vertical chopper (Blixer) at room temperature and at dry ice cryogenic conditions, followed by further subsample processing (20 g) using liquid nitrogen cryogenic conditions (cryomill). Analysis of the 43 targeted spiked and incurred contaminants in a food mixture consisting of equal parts orange, apple, kale, salmon, and croaker involved QuEChERS with automated mini-column solid-phase extraction (known as ITSP) cleanup followed by low pressure gas chromatography - tandem mass spectrometry (LPGC-MS/MS). Different ambient Blixer test portion sizes of 20, 10, 5, 2, and 1 g were assessed, and for cryogenic Blixer conditions, a 0.5 g test portion was also tested. In case of the cryomill, test portions were 2, 1, and 0.5 g, and all subsamples in all cases entailed 5 replicates. Determined concentrations and precisions (CV) of the analytes were compared to assess possible differences in systematic and random forms of error. A quality control spike was made before each step in the procedures to isolate that individual step in the uncertainty measurements using the error propagation sum of squares approach. Results indicated that the uncertainty of the sample preparation and LPGC-MS/MS analysis steps were 2-7% and 11% CV, respectively, while uncertainties of sample processing ranged from 6% CV for the cryomill to 12% CV for the ambient Blixer conditions. The common use of internal standards reduced overall method uncertainty from 12-15% to 7-10% CV. For the analytes, matrix, conditions, and tools used in this study, the minimal test sample weight that gave satisfactory recoveries and precision was found to be 1 g in all cases.