Previously, the Japanese Water Supply Act listed analysis of chlorate only in “Appendix No. 13: Simultaneous analysis by ion (anion) chromatography”. However, from April 1st 2020*, the analysis of chlorate was also added in “Appendix No. 18-2, analysis by LC/MS/MS". In addition to the use of ethylendiamine as an additive for the collected water sample, the use of sodium thiosulfate solution is now also allowed (1 - 2 mL of 0.3 % sodium thiosulfate (w/v) in 1-L water).
In this application, chlorate and bromate were analyzed by an LC/MS/MS method using RSpak JJ-50 4D, a multimode (reversed phase + anion exchange) column modified with quaternary ammonium groups. Calibration curves with good linearities were obtained for chlorate and bromate in the concentration range 0.001 - 0.02 mg/L.

*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