Simultaneous Determination of Amitraz and the Metabolites by Liquid Chromatography-Tandem Mass Spectrometry and Their Degradability by Disinfectant Use

The pesticide list for drinking water in Japan was revised on March 28, 2013, and the acaricide amitraz was listed as a target pesticide. We investigated an analytical method for the simultaneous determination of amitraz, and the metabolites N-2,4-dimethylphenyl-N-methylformamidine (DMPF) and 2,4-dimethylform- amidine (DMF) in water by liquid chromatography-tandem mass spectrometry. The optimal organic solvent content of the standard solution for preparing the calibration curve was 50 v/v% for amitraz, 1-10 v/v% for DMPF, and 5-50 v/v% for DMF to retain high stability and for preservation. In the fact-finding survey of the existence of the three substances in the Tama river, there were places where DMF was detected in trace amounts in May. We investigated the degradability of the three substances by a disinfectant sodium hypochlorite. As a result, amitraz disappeared in approximately 20 h, and DMPF disappeared shortly after addition of the disinfectant. On the other hand, although its amount was reduced by half in around 5 h, DMF decreased gradually afterwards, and its persistence was higher than those of amitraz and DMPF. It was suggested that amitraz and the metabolites DMF in tap water should be measured simultaneously.