HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY ATMOSPHERIC-PRESSURE CHEMICAL-IONIZATION MASS-SPECTROMETRY WITH IONIZATION POLARITY SWITCHING FOR THE DETERMINATION OF SELECTED PESTICIDES

A high performance liquid chromatographic/atmospheric pressure chemica l ionization mass spectrometric (APCI-MS) method has been developed fo r the determination of 10 pesticides. Initial comparison was made betw een the two atmospheric pressure ionization techniques, APCI and elect rospray, Optimum separation of the compounds was obtained using a Hype rsil carbamate column with a 0,05M ammonium acetate/acetonitrile isocr atic elution at a flow rate of 0.5 mL/min, A positive/negative ionizat ion mode switch was operated during each acquisition enabling the dete rmination of 8 of the compounds in the positive ionization mode and 2 of the compounds in the negative ionization mode. The method was appli ed to the determination of all 10 compouuds in extracts of strawberrie s and plums, Limits of detection were both compound and matrix depende nt and ranged from 0.002-0.025 ng/mu L in solvent-based standards and 0.003-0.05 ng/mu L in matrix-matched standards (equivalent to 0.002-0. 033 mg/kg in the crop), Where set, current Codex Alimentarius Commissi on and UK Maximum Residue Levels are clearly met by the sensitivity ac hieved by this method. (C) 1997 Crown Copyright.