Determination of amitraz and its transformation products in pears by ethyl acetate extraction and liquid chromatography-tandem mass spectrometry.

Abstract

A method has been developed for identification and quantification of the acaricide amitraz and its transformation products, 2,4-dimethylaniline (DMA), 2,4-dimethylformamidine (DMF) and N-2,4-dimethylphenyl-N-methylformamidine (DMPF) in pears. The analytes were extracted using ethyl acetate and anhydrous sodium sulphate. Analysis was performed by liquid chromatography-electrospray tandem mass spectrometry (LC-ESI-MS/MS) in the positive ion mode using a triple quadrupole (QqQ) instrument. Two precursor-product ion transitions were monitored for each compound in the selected reaction monitoring (SRM) mode. The method was validated with pears taken from the orchard before the amitraz treatment and spiked at the limit of quantification (LOQ), 10 times the LOQ and the maximum residue limit (MRL). Recoveries were between 70 and 106% and relative standard deviations were below 19% (n=5 at each spiked level). Excellent sensitivity resulted in limits of detection (LODs) for all the compounds below 10 microg kg(-1). Quantification was carried out using matrix-matched standards calibration, response was a linear function of the concentration from the LOQs to, at least, three orders of magnitude. Recoveries and standard deviations were comparable to those obtained after hydrolysis of amitraz and its metabolites to DMA. Occurrence of amitraz and its metabolites in field-treated pears showed that, seven days after the treatment, DMPF and DMF are the main degradation products. This work reports for the first time the use of a conventional pesticide multiresidue method and LC-ESI-MS/MS for determining amitraz and its metabolites in pears.