Abstract
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.
