Optimizing Recoveries of Planar Pesticides in Spinach Using Toluene and Agilent Bond Elut QuEChERS AOAC Kits with Graphitized Carbon

This application note describes the impact of toluene addition in the dispersive solid phase extraction (SPE) step on the analysis of pesticides in spinach using Agilent Bond Elut QuEChERS AOAC kits for highly pigmented fruits and vegetables. Graphitized carbon black (GCB) is required in the dispersive SPE kits in order to remove high levels of pigments from the matrix. However, it also retains pesticides with planar structures resulting in poor recovery and precision. The eight problematic pesticides found in the original AOAC method, by either LC/MS/MS or GC/MS, generated poor results with about 20% to 60% recovery with >15% relative standard deviation (RSD). In the modified AOAC method, an aliquot of toluene was added to the dispersive SPE clean-up tube, in a ratio of 8:3 (acetonitrile (ACN) extracts/toluene). It significantly improved the extraction efficiency of the problematic planar pesticides. With the modified AOAC method, the eight problematic pesticides generated substantially improved recoveries, 50% to 100%, and < 10% RSD. However, the addition of toluene also introduced more matrix impurities into the final sample, and caused problems for some pesticides which gave good results originally. Therefore, the modified AOAC method cannot be considered a "drop in" replacement for the original AOAC method; but it can be a very useful alternative for the problematic pesticides affected by GCB in the pesticides analysis of highly pigmented matrix. Authors Limian Zhao, Joan Stevens Agilent Technologies, Inc. 2850 Centerville Road Wilmington, DE 19809-1610 USA Application Note