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A combination of fast GC with narrow-bore column and bench top quadrupole mass spectrometer (MS) detector in negative chemical ionization (NCI) mode (with methane as reagent gas) is set up and utilized for the ultratrace analysis of 25 selected pesticides. The observed pesticides, belonging to the endocrine disrupting chemicals (EDCs), were from different chemical classes. A comparative study with electron impact (EI) ionization was also carried out (both techniques in selected ion monitoring (SIM) mode). The programmed temperature vaporizer (PTV) injector in solvent vent mode and narrow-bore column (15mx0.15mm I.D.x0.15microm film of 5% diphenyl 95% dimethylsiloxane stationary phase) were used for effective and fast separation. Heptachlor (HPT) as internal standard (I.S.) was applied for the comparison of results obtained from absolute and normalized peak areas. Non-fatty food matrices were investigated. Fruit (apple - matrix-matched standards; orange, strawberry, plum - real samples) and vegetable (lettuce - real sample) extracts were prepared by a quick and effective QuEChERS sample preparation technique. Very good results were obtained for the characterization of fast GC-NCI-MS method analysing EDCs pesticides. Analyte response was linear from 0.01 to 150microgkg(-1) with the R(2) values in the range from 0.9936 to 1.0000 (calculated from absolute peak areas) and from 0.9956 to 1.0000 (calculated from peak areas normalized to HPT). Instrument limits of detection (LODs) and quantification (LOQs) were found at pgmL(-1) level and for the majority of analytes were up to three orders of magnitude lower for NCI compared to EI mode. In both ionization modes, repeatability of measurements expressed as relative standard deviation (RSDs) was less than 10% which is in very good agreement with the criterion of European Union.

The study of pesticide residues belonging to endocrine disrupting chemicals (EDCs) (23 analytes of different chemical classes--organochlorines, organophosphates, pyrethroids, dicarboximides, phtalamides, dinitroanilines, pyrazole, triazinone) in apple matrix with conventional capillary GC-NCI-MS (with methane as reagent gas) in comparison to EI ionization is presented. For sample preparation QuEChERS method was applied. The lowest calibration levels (LCLs) for all pesticides were determined in both modes. Calibration in the NCI mode was performed at the concentration levels from 0.1 to 500 microg kg(-1) (R(2) > 0.999) and for EI in the range from 5 to 500 microg kg(-1) (R(2) > 0.99). From LCLs the instrumental limits of detection (LODs) and quantification (LOQs) were calculated. Chemometric study of pesticide signals in two MS modes was performed. Repeatability of all measurements, expressed by the relative standard deviations of absolute peak areas was better than 10% for the majority of compounds. Significantly lower values were obtained for the NCI mode.

Fast GC-MS with narrow-bore columns combined with effective sample preparation technique (QuEChERS method) was used for evaluation of various calibration approaches in pesticide residues analysis. In order to compare the performance of analyte protectants (APs) with matrix-matched standards calibration curves of selected pesticides were searched in terms of linearity of responses, repeatability of measurements and reached limit of quantifications utilizing the following calibration standards in the concentration range 1-500 ng mL(-1)(the equivalent sample concentration 1-500 microg kg(-1)): in neat solvent (acetonitrile) with/without addition of APs, matrix-matched standards with/without addition of APs. For APs results are in a good agreement with matrix-matched standards. To evaluate errors of determination of concentration synthetic samples at concentration level of pesticides 50 ng mL(-1) (50 microg kg(-1)) were analyzed and quantified using the above given standards. For less troublesome pesticides very good estimation of concentration was obtained utilizing APs, while for more troublesome pesticides such as methidathion, malathion, phosalone and deltamethrin significant overestimation reaching up to 80% occurred. According to presented results APs can be advantegously used for "easy" pesticides determination. For "difficult" pesticides an alternative calibration approach is required for samples potentially violating MRLs. An example of real sample measurement is shown. In this paper also the use of internal standards (triphenylphosphate (TPP) and heptachlor (HEPT)) for peak areas normalization is discussed in terms of repeatability of measurements and quantitative data obtained. TPP normalization provided slightly better results than the use of absolute peak areas measurements on the contrary to HEPT.