Evaluation of different calibration approaches in pesticide residues analysis in non-fatty food using fast GC-MS

In the analysis of pesticide residues by GC including GC-MS, adverse effects caused by matrix co-extractives occurs which results in worse precision and trueness of analytical results. Sample extracts of various commodities (fruit and vegetables), prepared by the QuEChERS method were evaluated by gravimetric analysis to compare co-extracted compounds amount. For comparison of matrix background measurement of acetonitrile (MeCN) extracts in full scan mode and SIM monitoring were performed utilising fast GC-MS with quadrupole analyser and narrow-bore columns. In order to evaluate the trueness of quantitative analysis results utilising different calibration standards experiments with synthetic samples (it is a blank sample extract from selected fruit and vegetables - apples, pear, cucumbers and cauliflowers, with the addition of pesticides at the concentration level of 0.05 ng mu L-1 (50 mu g kg(-1))) were performed in this work. This sample represents a simulated real sample, but with the known concentration to check the various calibration approaches utilising calibration standards that would be used in practice: (1) in organic solvent (MeCN) with addition of analyte protectants (APs), (2) matrix-matched standard, (3) matrix-matched standard with addition of APs. For most of studied pesticides very good match of concentration was obtained utilising matrix matched standards (with/without APs). For the majority of the pesticides under study significant overestimation of concentration was observed in acetonitrile standards with APs in all matrices. Repeatability of measurements expressed as relative standard deviations (RSDs) of determined pesticides concentration in all tested matrices was <= 14%.