Blind Analysis of Fortified Pesticide Residues in Carrot Extracts using GC-MS to Evaluate Qualitative and Quantitative Performance

Authors: Lehotay, Steven; Gates, Robert

Submitted to: Journal of Separation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/10/2009
Publication Date: 10/1/2009
Citation: Lehotay, S.J., Gates, R.A. 2009. Blind Analysis of Fortified Pesticide Residues in Carrot Extracts using GC-MS to Evaluate Qualitative and Quantitative Performance. Journal of Separation Science. 32:3706-3719.

Interpretive Summary: Pesticide residue analysis requires analytical chemists to determine what pesticides are in the monitored food samples. Gas chromatography coupled to mass spectrometry (GC-MS) is one of the most important techniques used to detect and measure the trace residues. Analytical chemists have devised criteria for pesticide identification in the samples using GC-MS, and this study evaluates the choice of these criteria for selected pesticides in carrots to determine if they correctly identify pesticides added to the samples unknown to the analyst. Each pesticide had different characteristics that made it difficult to apply a single set of GC-MS identification criteria that was optimal for all pesticides. Analyst familiarization training and the use of more flexible criteria minimize the chances of mistakes and false accusations made in the regulatory arena.

Technical Abstract: Unlike quantitative analysis, the quality of the qualitative results in the analysis of pesticide residues in food are generally ignored in practice. Instead, chemists tend to rely on advanced mass spectrometric 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 done in quantitative method validation studies, collection of distinguishing factors of selectivity vs. concentration 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 can be done, at least to better evaluate detection limits and reduce the chances of a serious qualitative problem. Familiarization training and review of results by the analyst(s) increases 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 empirical approach to evaluate gas chromatography – mass spectrometry (GC-MS) using selected ion monitoring (SIM) with a quadrupole instrument and 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 were found to be superior for all analytes.