ARS | Publication request: Effects of temperature and purity of magnesium sulfate during extraction of pesticides residues using the QuEChERS method

Submitted to: Official Methods of Analysis of AOAC International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 13, 2011
Publication Date: October 13, 2012
Citation: Geis-Asteggiantel, L., Lehotay, S.J., Heinzen, H. 2012. Effects of temperature and purity of magnesium sulfate during extraction of pesticides residues using the QuEChERS method. Official Methods of Analysis of AOAC International. 95(5)1311-1318.

Interpretive Summary: Although the quick, easy, cheap, effective, rugged, and safe (QuEChERS) approach has become the most common sample preparation method in the world used to monitor pesticide residues in fruits and vegetables, it still has difficulties with a few unstable fungicides. These include chlorothalonil, captan, captafol, and folpet, which are commonly applied to many commodities. This study involved the use of an ice bath and different purities of chemical reagents during sample preparation to lower temperature and reduce degradation of the unstable fungicides. The results showed that the lower purity reagents worked equally well as the high purity material, and lower temperature improved results in broccoli samples, but the general problem with the unstable fungicides still remained. This study serves as an additional contribution to the scientific literature to benefit current and future chemists worldwide who monitor pesticide residues in food.

Technical Abstract: Despite its many documented advantages, the QuEChERS (quick, easy, cheap, effective, rugged and safe) sample preparation approach has problems with a few unstable pesticides, partly due to the exothermic reaction generated by the use of anhydrous magnesium sulfate during extraction. These pesticides also tend to be difficult to analyze by gas chromatography – mass spectrometry (GC-MS). The aim of this study was to evaluate the effect of temperature during the extraction process in a revised version of AOAC Official Method 2007.01 using anh. MgSO4 =99% (fine powder) or =97% (granular) purity; and the use of an ice bath for particular unstable pesticides of interest (chlorothalonil, captan, captafol, folpet, and the degradation products cis-1,2,3,6-tetrahydrophthalimide and phthalimide). Recoveries of 38 representative pesticides were measured in lime and broccoli at different extraction conditions by liquid chromatography – tandem mass spectrometry (LC-MS/MS) and low pressure gas chromatography – tandem mass spectrometry (LP-GC-MS/MS). Results showed that the difference in temperature when using 99% vs. 97% purity anh. MgSO4 was 6-9 degrees C, which did not lead to significant differences in recoveries. The use of an ice bath aided recovery for some of the analytes in broccoli, but no significant differences were observed for limes, which already provided greater stability of the base-sensitive analytes due to acidity of the matrix.