Liquid chromatography electrospray mass spectrometry multiresidue determination of pesticides in apples and pears

This paper describes a rapid, specific and sensitive multi-residue method f or the routine quantitative analysis of pesticides of several classes used for the treatment of apples and pears, down to their respective maximum res idue limits (MRLs). It involves a rapid extraction procedure and liquid chr omatography coupled to electrospray mass selective detection. Seven pestici des were extracted at pH 4.5 with a mixture of acetone-dichloromethane-hexa ne (50.20:30, v/v/v). Ionization was performed at atmospheric pressure in a n electrospray-type source and detection was carried out using the selected ion monitoring (SIM) mode. Extraction recoveries were between 55 and 98% e xcept for methylthiophanate (<20%). Limits of detection (LODs) and limits o f quantitation (LOQs) ranged, respectively, from 0.01 to 0.02 mg/kg and fro m 0.02 to 0.05 mg/kg, with relative standard deviation (R.S.D.) less than 1 9%. An excellent linearity was observed for LOQs up to 5 mg/kg. Intermediat e ("inter-assay") precision and accuracy were satisfactory. The method was applied to many fruit samples intended for commercialisation. (C) 1999 Else vier Science B.V. All rights reserved.