We developed a liquid chromatograph-tandem mass spectrometer (LC-MS/MS) analysis method for the simultaneous determination of methidathion-oxon, which was added as the “Complimentary Items” in drinking water. Furthermore, we conducted a validation test along with 18 laboratories to confirm that the analytical method developed in the present study is applicable to various types of drinking water and instruments. Recovery tests of the methidathion-oxon spiked into drinking water were performed in two set points (0.03μg/L and 0.3μg/L), which are below 1/100 and 1/10 of target values of methidathion (0.004mg/L) in drinking water in Japan. After dechlorinated with sodium ascorbate or sodium thiosulfate, standard solution of methidathion-oxon was added to tap water collected in each laboratory. The linearity of calibration curves, selectivity, accuracy (recovery), repeatability, and intermediate precision were evaluated in this study. Proper ranges of calibration curves should be selected for the determination of these anions because the range of the linearity of calibration curves differed depending on the instruments. The accuracy, repeatability, and intermediate precision obtained by the recovery tests satisfied the criteria in the guideline for the validation of the testing method for drinking water provided by the Ministry of Health, Labour and Welfare, Japan. Therefore, we concluded that the analytical method evaluated in the present study is valid for the analysis of methidathion-oxon in drinking water.

View full abstract

[in Japanese]

View full abstract