Rapid and sensitive ultra-high-pressure liquid chromatography–quadrupole time-of-flight mass spectrometry for the quantification of amitraz and identification of its degradation products in fruits

Liquid chromatography under high pressure in combination with quadrupole time-of-flight mass spectrometry (QqTOF-MS and MS/MS) has been used to detect amitraz degradation products in pears, to characterize their structures, and to evaluate their occurrences in samples of different origins. Using the proposed approach, the parent pesticide and four degradation products were identified. To this end, pear samples were extracted with ethyl acetate and anhydrous sodium sulphate. Amitraz was found to be rapidly decomposed into four related compounds, of which N-(2,4-dimethylphenyl)formamidine (DMPF) was the most abundant and persistent. N,N′-bisdimethylphenylformamidine (BDMPF), 2,4-dimethylformamidine (DMF) and 2,4-dimethyl aniline (DMA) were also main metabolites of amitraz. To our knowledge this is the first report that confirms the presence of BDMPF in pears. The method was validated using MS and MS/MS for those standard available (analytical or not). In MS, recoveries ranged from 83 to 101% with relative standard deviation (RSD) from 9 to 19% at the limit of quantification (LOQ) (between 5 and 20 μg kg−1). Using MS/MS, recoveries, linearity and precision were similar but LOQs were higher because the intense fragmentation of the protonated molecules in the product mass spectrum. BDMPF, as an approximation, was quantified based on the DMF metabolite. The results demonstrated that high-pressure LC–QqTOF-MS and MS/MS techniques enhance further the capabilities of LC–MS in the identification of polar species in complex food samples.