Analysis of "Amitraz (sum)" in pears with incurred residues - Comparison of the approach covering the individual metabolites via LC-MS/MS with the approach involving cleavage to 2,4-dimethylaniline.

We developed a method for the hydrolysis of amitraz, and its degradation products 2,4-dimethylphenyl-N'-methylformamidine (DMPF) and 2,4-dimethylformamide (DMF) into 2,4-dimethylaniline (DMA), directly from QuEChERS extracts. The hydrolysis product DMA was analysed using liquid chromatography-electrospray tandem mass spectrometry (LC-ESI-MS/MS) in the positive ion mode with DMA D6 as an internal standard. Validation of DMPF and amitraz via DMA, following hydrolysis directly from the QuEChERS raw extracts, was performed at 0.05 mg kg(-1) and at 0.5 mg kg(-1). Individual recoveries of amitraz and DMPF, determined as DMA, ranged between 100 and 120% and between 96 and 118% respectively and the relative standard deviations (RSDs) below 5.2% and below 9.5% respectively (n=5 at each spiked level). Successful validation for amitraz, and DMPF at 0.01 mg kg(-1), was also conducted following fivefold pre-concentration of QuEChERS extracts prior to hydrolysis. Pear samples with a history of amitraz treatment, containing residues of the amitraz metabolite DMPF but no detectable residues of amitraz or its other metabolites, DMF and DMA, were extracted using the QuEChERS method. DMPF-results obtained using direct LC-MS/MS analysis were found to be comparable with DMA-results obtained when the same extracts were subjected to alkaline hydrolysis, suggesting that DMPF constituted virtually the only source of DMA in the analysed pears and that the determination of amitraz (sum) in pears does not necessarily require a cumbersome method involving cleavage to DMA.