Cryogenic sample processing with liquid nitrogen for effective and efficient monitoring of pesticide residues in foods and feeds

Authors: ROUSSEY, MANOL - UNIVERSITY OF HUMBOLT; Lehotay, Steven; POLLAEHNE, JULIUS - UNIVERSITY OF HUMBOLT

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/31/2019
Publication Date: 8/1/2019
Citation: Roussey, M., Lehotay, S.J., Pollaehne, J. 2019. Cryogenic sample processing with liquid nitrogen for effective and efficient monitoring of pesticide residues in foods and feeds. Journal of Agricultural and Food Chemistry. 67(33):9203-9209. https://doi.org/10.1021/acs.jafc.9b04006.
DOI: https://doi.org/10.1021/acs.jafc.9b04006

Interpretive Summary: Pesticide residue analysis of foods is conducted in thousands of laboratories worldwide for food safety, regulatory control, international food trade, risk assessment, monitoring, and other purposes. Sample processing of the bulk sample collected from a warehouse, ship, silo, train car, farmer’s field, or other source is an essential part of the overall analysis to yield accurate and meaningful findings, but this step is generally neglected by chemists and common practices are assumed to be acceptable. This may have been true in the past, but many investigators using miniaturized techniques are ignoring the importance of sample processing, rendering their studies useless if the tested portion does not represent the original bulk sample. In this study, the practical and safe use of liquid nitrogen for bulk sample processing and its benefits are described and demonstrated. Liquid nitrogen is cleaner, cheaper, and more effective than dry ice, and it is anticipated that many other laboratories in the world will also begin to use this approach for achieving improved pesticide residue analytical results.

Technical Abstract: When monitoring hundreds of pesticides in food and feed, the comminution step is equally crucial as any other to achieve valid results. However, sample processing is often underestimated in its importance and practical difficulty to produce consistent test portions for analysis. The scientific literature is rife with descriptions of micro-extraction methods, but ironically, sample comminution is often ignored or dismissed as being prosaic, despite that it is the foundation upon which the viability of such techniques relies. Cryogenic sample processing using dry ice (-78°C) is generally accepted in practice, but studies have not shown it to yield representative test portions < 1 g. Remarkably, liquid nitrogen has rarely been used as a cryogenic agent in pesticide residue analysis, presumably due to access, cost, and safety concerns. Yet, real-world implementation of blending unfrozen bulk food portions with liquid nitrogen (-196°C) using common food processing devices has demonstrated this approach to be safe, simple, fast, cost-effective, and yield high quality results for various commodities, including increased stability of labile or volatile analytes. For example, analysis of dithiocarbamates as carbon disulfide has shown a significant increase of thiram recoveries (up to 95%) by using liquid nitrogen during sample comminution. This perspectives article is intended to allay concerns among working laboratories about the practical use of liquid nitrogen for improved sample processing in the routine monitoring of pesticide residues in foods and feeds, which also gives promise for feasible test sample size reduction in high-throughput miniaturized methods.