Summar yIn order to adopt "screening analysis" in drinking water quality testing, which performs qualitative and quantitative analysis based on information registered in a database without measuring standard materials at the time of each testing, a validation test was conducted to evaluate the difference on the chromatogram data analysis by analysts. In the validation test, chromatograms of 6 water samples were analyzed using the same database and software by 16 analysts in 13 laboratories. Peak identification was performed based on Retention time (RT), (qualifier and target ion) QT ratio, and degree of matching of mass spectra, and if necessary, peak shapes in water samples were compared with those in calibration curve samples. Large differences were observed in the detection of pesticides among the analysts. There were two main reasons for the disagreement. The first is that the judgement of peak detection at low concentrations near the quantification limit of each pesticide, particularly below the concentration at three times of quantification limit, differed depending on the analyst. The other reason was that some analysts made clear misidentifications and identified wrong peaks close to the predicted retention time, despite the QT ratio and mass spectrum didnʼt match that in the database. In addition, there were some cases where the quantified values were reported by misidentifying the peaks of degradation products and metabolites, even when the peak detection was correctly judged. In order to use screening analysis practically by drinking water quality testing laboratories, it is important to conduct a validation test like this study in advance to use screening analysis and to coordinate criteria for peak identification and quantification among data analysts.
We developed a liquid chromatography-tandem mass spectrometry (LC/MS/MS) analysis method for the simultaneous determination of 141 agricultural chemicals, the "Complimentary Items" in tap water in the Japanese Waterworks Act. Furthermore, we evaluated the validity of the analytical method on the basis of the results of the recovery tests performed with two set points, that is 1/10 of the desired value and 1/100 of the desired value of each agricultural chemical in the Japanese Waterworks Act. For 129 agricultural chemicals (when dechlorinated with sodium ascorbate) or 127 agricultural chemicals (when dechlorinated with sodium thiosulfate) , the quantification limits were lower than 1/10 of the desired values of each chemical, and the accuracy (recovery ratio) and repeatability also satisfied the criteria. For 120 agricultural chemicals, the quantification limits were lower than 1/100 of the desired values of each chemical, and the accuracy (recovery ratio) and repeatability satisfied the criteria of the Japanese guideline concerning water quality analysis. Therefore, we judged that our simultaneous analytical method developed in the present study is applicable to the analysis of 120 agricultural chemicals in drinking water. However, we should select the dichlorination treatment agent in accordance with the target chemicals.
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