Submitted to: Journal of Association of Official Analytical Chemists International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/6/2004
Publication Date: 3/22/2005
Citation: Lehotay, S.J., Mastovska, K., Lightfield, A.R. 2005. Use of buffering to improve results of problematic pesticides in a fast and easy method for residue analysis of fruits and vegetables. Journal of Association of Official Analytical Chemists International. 88.pp. 615-629. Interpretive Summary: Pesticide residue analysis of foods is a main function of many analytical laboratories around the world. The current methods used in analysis are time-consuming, laborious, and expensive. A "quick, easy, cheap, effective, rugged, and safe" (QuEChERS) method for analysis of pesticide residues in food was recently introduced to provide a much more efficient way to better meet laboratory needs. However, a few problematic pesticides remained in the method, and this study demonstrates how the use of buffering in the procedure solves the problems associated with sample preparation of these pesticides. Excellent results were obtained for notoriously difficult-to-detect pesticides. This buffered approach will be used in an interlaboratory validation study in the future, and the QuEChERS method will likely replace the inefficient monitoring methods currently in use.
Technical Abstract: A modification that entails the use of buffering during extraction was made to further improve results for certain problematic pesticides (e.g., folpet, dichlofluanid, chlorothalonil, pymetrozine) in a simple, fast, and inexpensive method for the determination of pesticides in produce. The method, known as the quick, easy, cheap, effective, rugged, and safe (QuEChERS) method for pesticide residues in foods, now involves the extraction of the sample with acetonitrile (MeCN) containing 1% acetic acid (HAc) and simultaneous liquid-liquid partitioning formed by adding anhydrous magnesium sulfate (MgSO4) plus sodium acetate (NaAc). The extraction method is carried out by shaking a Teflon centrifuge tube which contains 1 mL of 1% HAc in MeCN plus 0.4 g anh. MgSO4 and 0.1 g anh. NaAc per g sample. The tube is then centrifuged, and a portion of the extract is transferred to a tube containing 50 mg primary secondary amine (PSA) sorbent plus 150 mg anh. MgSO4 per mL extract. After a mixing and centrifugation step, the extract is transferred to autosampler vials for concurrent analysis by gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/tandem mass spectrometry (LC/MS-MS). The use of buffering during the extraction maintains pH of 4-5 independent of commodity, which minimizes degradation of base-sensitive pesticides and increases recovery of the most basic pesticide, pymetrozine, in acidic matrices. The method was evaluated for 32 diverse pesticides in different matrices, and typical %recoveries were 95 ± 10 even for some problematic pesticides.