Rapid and Effective Pass-Through Cleanup of High Chlorophyll QuEChERS Extracts Prior to GC-MS/MS and LC-MS/MS Analysis

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Michael S. Young, Kim Tran and Jeremy C. Shia
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In recent years, food safety laboratories have adopted new and simplified sample preparation methods designed to reduce analysis time and related costs, as well as to increase throughput.  For example, the QuEChERS methods for fruits and vegetables require only minutes for sample preparation and replace prior methods that took hours or days.  In this study, this type of simplified sample preparation is applied to pesticide analysis in spinach, a leafy vegetable matrix high in chlorophyll and other pigments.  In the QuEChERS extraction, significant amounts of chlorophyll and other pigments are co-extracted along with the target pesticides.  The presence of these co-extracted substances can lead to chromatographic interference, contamination of the GC injector and column, contamination of the column and other components of the UPLC system and contamination of the mass spectrometer itself.  To avoid these complications, a cleanup step is recommended prior to the instrumental analysis.   For spinach, this is often performed using dispersive SPE (dSPE) with graphitized carbon black (GCB) or other sorbents designed to remove chlorophyll. In this study, chlorophyll and other natural pigments in a raw spinach sample, such as lutein and carotene, were measured using UHPLC with photodiode array detection (PDA).  Then various types of dispersive and pass-through SPE cleanup options were evaluated for pigment removal (monitored using PDA) and pesticide recovery (monitored using GC-MS/MS and LC-MS/MS). Particular attention was given to recoveries of planar pesticides commonly used on spinach

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