Under the “Methods Prescribed by the Minister of Health, Labour and Welfare Based on the Provisions of the Ordinance on Water Quality Standards” (MHLW Notification No. 261, July 22, 2003; last amended by Notification No. 95*, March 25, 2020), chlorate was added, alongside bromate, as a target analyte in “Table 18-2: Liquid Chromatography–Mass Spectrometry (LC–MS/MS)”. To suppress the formation of chlorate from chlorite caused by residual chlorine, the method permits the use of sodium thiosulfate solution in addition to the use of ethylenediamine (EDA) solution at the time of sample collection (0.3 % sodium thiosulfate (w/v) solution, 1–2 mL per 1 L of sample). The method in Table 18-2 mentions using a column packed with silica or polymer-based gels modified with anion‑exchange group, or a column offering equivalent or superior separation performance. Using RSpak JJ-50 2D, a multimode (reversed phase and anion exchange) column modified with quaternary ammonium group, we analyzed (1) tap water spiked with chlorate and bromate and (2) tap water treated with sodium thiosulfate. Under the described conditions, JJ-50 2D enabled the analysis of chlorate and bromate without interference from sodium thiosulfate. The calibration curves for both analytes showed high linearity over 0.001 to 0.02 mg/L.
**Target analytes in Table 18-2 include chlorate and bromate.

*The version at the time of the application acquisition.

Sample: 5 µL
(Tap water spiked with standards) 10 µg/L each of ClO₃^-, and BrO₃^- in tap water containing 0.0003 % sodium thiosulfate (w/v)

1. 1.ClO₃^-, Chlorate
2. 2.BrO₃^-, Bromate
3. 3.HS₂O₃^2-, Thiosulfate with one hydrogen ion attached

Sample: 5 µL
Tap water containing containing 0.0003 % sodium thiosulfate (w/v)

1. 1.ClO₃^-, Chlorate
2. 2.BrO₃^-, Bromate
3. 3.HS₂O₃^2-, Thiosulfate with one hydrogen ion attached