Submitted to: Analytical and Bioanalytical Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2018
Publication Date: 2/6/2018
Citation: Lehotay, S.J., Han, L., Sapozhnikova, Y.V. 2018. Use of a quality control approach to assess measurement uncertainty in the comparison of sample processing techniques in the analysis of pesticide residues in fruits and vegetables. Analytical and Bioanalytical Chemistry. 2018:1-15.
DOI: https://doi.org/10.1007/s00216-018-0905-1 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 pesticide residues in 10 fruits and vegetables, and results showed that processing the samples at room temperature generally meets regulatory needs. This finding means that labs can use the simpler, faster, and cheaper approach to sample processing when monitoring pesticide residues in food.
Technical Abstract: In routine monitoring of foods, reduction of analyzed test portion size generally leads to higher sample throughput, less labor, and lower costs of monitoring, but to meet analytical needs, the test portions still need to accurately represent the original bulk samples. With the intent to determine minimal fit-for-purpose sample size, analyses were conducted for up to 93 incurred and added pesticide residues in 10 common fruits and vegetables processed using different sample comminution equipment. The commodities studied consisted of apple, banana, broccoli, celery, grape, green bean, peach, potato, orange, and squash. A Blixer was used to chop the bulk samples at room temperature, and test portions of 15, 10, 5, 2, and 1 g were taken for analysis (n = 4 each). Additionally, 40 g subsamples (after freezing) were further comminuted using a cryomill device with liquid nitrogen, and test portions of 5, 2, and 1 g were analyzed (n = 4 each). Both low-pressure gas chromatography - tandem mass spectrometry (LPGC-MS/MS) and ultrahigh-performance liquid chromatography (UHPLC)–MS/MS were used for analysis. An empirical approach was followed to isolate and estimate the measurement uncertainty contribution of each step in the overall method by adding quality control spikes prior to each step. Addition of an internal standard during extraction normalized the sample preparation step to 0% error contribution, and coefficients of variation (CVs) were 6-7% for the analytical steps (LC and GC) and 6-9% for the sample processing techniques. In practice, overall CVs averaged 9-11% among the different analytes, commodities, batches, test portion weights, and analytical and sample processing methods. On average, CVs increased up to 4% and bias 8-12% when using 1-2 g test portions vs. 10-15 g.