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Abstract: Gas and liquid chromatography (GC and LC) coupled to mass spectrometry (MS) serve as the most powerful analytical tools commonly used to monitor pesticide residues in food, among other applications. However, both GC–MS and LC–MS are susceptible to matrix effects which can adversely affect quantification depending on the analyte, matrix, sample preparation, instrumentation, and operating conditions. Among the approaches that reduce matrix effects, the most common in pesticide residue applications is matrix-matched calibration because it is relatively inexpensive and simple. Also, it has been shown to work well during method validation when fortified samples are exactly matched with samples used for calibration. However, the quality of matrix-matched results in real-world analyses depends on the consistency of matrix effects among diverse samples. In this study, the variability of matrix effects was measured for 38 representative pesticides in 20 samples each (including different varieties) of rice, orange, apple, and spinach extracted using the “quick, easy, cheap, effective, rugged, and safe” (QuEChERS) method for analysis by LC–MS/MS and low-pressure GC–MS. Using LC–MS/MS, only oranges gave >20% matrix effects for a few pesticides. GC–MS exhibited larger matrix effects, but as in LC–MS/MS, the differences were reasonably consistent among the 20 samples tested. Main conclusions of this study are that for the conditions utilized: (1) matrix-matching was not needed for most pesticides in the simpler food matrices; and (2) for the more complex orange matrix, acceptably accurate quantitative results were achieved by using matrix-matching even with a different sample of the same type. However, full confidence cannot be extended to matrix-matched results, and for consequential applications such as regulatory enforcement, confirmatory analyses using alternate quantitative determinations should also be conducted. [Copyright &y& Elsevier]

Abstract: Matrix matching is used in analysis to compensate for matrix effects that influence analytical response. It has been a widely discussed topic in electro-spray mass spectrometry where the ionization suppression is a major problem in accurate quantitative analysis. However, the unique strength of mass spectrometry to detect and quantify accurately a co-eluting stable isotope labelled internal standard offers an easy solution to the ionization suppression problem. Given the fact that it is impossible to match the matrix of the calibration standards with all samples, mass spectrometry allows accurate quantitation without the need for matrix matching, as long as the internal standard co-elutes with the analyte of interest. If the analyte and internal standard co-elute, the slope of the calibration curve analyte response/internal standard vs. analyte concentration is independent of the matrix composition, eliminating the need for matrix matching. [Copyright &y& Elsevier]