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item Lehotay, Steven

Submitted to: Journal of Association of Official Analytical Chemists International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2004
Publication Date: 4/10/2005
Citation: Lehotay, S.J., Mastovska, K., Jong, Y. 2005. Evaluation of two fast and easy methods for pesticide residue analysis in fatty food matrices. Journal of Association of Official Analytical Chemists International. 88. pp. 630-638.

Interpretive Summary: Pesticide residue analysis of both nonfatty and fatty foods is a main function of many analytical laboratories around the world. The current methods used in analysis are time-consuming, laborious, and expensive, especially in the case of fatty foods due to the need to remove co-extracted lipids before the detection step. Two easier alternate methods of pesticide analysis are matrix solid-phase dispersion (MSPD) and the "quick, easy, cheap, effective, rugged, and safe" (QuEChERS) method, which has been shown to be effective in the analysis of nonfatty foods. This study was designed to evaluate and compare the two rapid methods for the analysis of 32 diverse pesticides fortified in milk, egg, avocado and other fatty foods. The QuEChERS method was adapted slightly by adding a sorbent to remove lipids during the cleanup step. Excellent results were obtained for certain problematic residues by the QuEChERS method that were not recovered by the MSPD method. However, recoveries in both methods for the most nonpolar (lipophilic) pesticides decreased as fat content in the sample increased, but to a lesser extent in the MSPD method. The QuEChERS method is the faster and easier of the alternate methods, and gives good recoveries for all tested pesticides in milk, eggs, and similar foods with <15% lipid content. It also works well for all but the most lipophilic pesticides in foods with fat content >15%. Relatively few foods contain >15% fat, and it likely that the QuEChERS method will become commonly used for many pesticide monitoring applications in the future.

Technical Abstract: Two rapid methods of sample preparation and analysis of fatty foods (e.g. milk, eggs, and avocado) were evaluated and compared for a wide range of 32 pesticide residues. One method, dubbed the "quick, easy, cheap, effective, rugged, and safe" (QuEChERS) method for pesticide residue analysis, entailed extraction of 15 g sample with 15 mL acetonitrile (MeCN) containing 1% acetic acid followed by addition of 6 g anhydrous magnesium sulfate and 1.5 g sodium acetate. After centrifugation, 1 mL of the buffered MeCN extract underwent a cleanup step using 50 mg each of C18 and primary secondary amine (PSA) sorbents plus 150 mg MgSO4 (a technique known as dispersive solid-phase extraction). The second method incorporated a form of matrix solid-phase dispersion (MSPD), in which 0.5 g sample plus 2 g sodium sulfate was mixed in a mortar and pestle and added above a 2 g Florisil column on a vacuum manifold. Then, 5 x 2 mL MeCN was used to elute the pesticide analytes from the sample into a collection tube, and the extract was concentrated to 0.5 mL. Extracts in both methods were analyzed concurrently by gas chromatography/mass spectrometry and liquid chromatography/tandem mass spectrometry. The recoveries of semi-polar and polar pesticides were typically 100% in both methods (except basic pesticides, such as thiabendazole and imazalil, were not recovered in the MSPD method), but recovery of nonpolar pesticides decreased as fat content of the sample increased. This trend was more pronounced in the QuEChERS method, in which case the most lipophilic analyte tested, hexachlorobenzene, gave 27 ± 1 %recovery (n = 6) in avocado (15% fat) with < 10 ng/g limit of quantitation.