Blind analysis of fortified pesticide residues in carrot extracts using GC-MS to evaluate qualitative and quantitative performance.

Unlike quantitative analysis, which must commonly undergo an extensive method validation process in labs to assure quality of results, the quality of the qualitative results in the analysis of pesticide residues in food is generally ignored in practice. Instead, chemists tend to rely on advanced MS techniques and general subjective guidelines or fixed acceptability criteria when making analyte identifications. All analytes and matrices have unique characteristics that make this current approach less effective than desirable in many real-world situations. Just as performed in quantitative method validation studies, collection of distinguishing factors of selectivity versus concentration, such as analyte retention time variabilities, ion ratios, matrix background evaluations, choice of ions, and the number of ions to use, provides specific information about the particular application to assess its quality. Empirical analysis of many blind samples to check the rates of false positives and negatives should be performed, at least to better evaluate LOD and reduce the chances of a serious qualitative problem. Familiarization training and review of results by the analyst(s) increase performance, and in any case, the traditional use of two independent analyses should still be relied upon to make chemical confirmations. In this study, an experimental approach to evaluate GC-MS using SIM with a quadrupole instrument and an MS/MS (ion trap) was conducted to assess the qualitative factors of both methods for 16 pesticides fortified (or not) in carrot extracts. Rates of false positives and negatives were compared using different identification criteria, and no single set of conditions was found to be superior for all analytes.