On March 25th 2020, the Japanese Water Supply Act added chlorate 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. RSpak JJ-50 4D, a multimode (reversed phase + anion exchange) column modified with quaternary ammonium groups, is suitable for the simultaneous analysis of not only chlorate and bromate, but other anions and haloacetic acids by following the analytical conditions mentioned in the Appendix 18-2. We observed that the elution times of two additives were different: thiosulfate ion elutes after sulfate ion while ethylendiamine elutes before any other anions.

Sample : 5 μL
10 μg/L each for ClO₃^-, BrO₃^-
100 μg/L each for MCAA, DCAA, TCAA
in Tap water containing sodium thiosulfate 0.3 w/v%

1. 1.ClO₄^-, Perchlorate
2. 2.TCAA, Trichloroacetic acid
3. 3.ClO₃^-, Chlorate
4. 4.DCAA, Dichloroacetic acid
5. 5.NO₃^-, Nitrate
6. 6.MCAA, Chloroacetic acid
7. 7.BrO₃^-, Bromate
8. 8.Br^-, Bromide
9. 9.Cl^-, Chloride
10. 10.HSO₄^-, Hhydrogen sulfate
11. 11.S₂O₃^2-, Thiosulfate

Sample : 5 μL
Tap water containing sodium thiosulfate 0.3 w/v%

1. 1.ClO₄^-, Perchlorate
2. 2.TCAA, Trichloroacetic acid
3. 3.ClO₃^-, Chlorate
4. 4.DCAA, Dichloroacetic acid
5. 5.NO₃^-, Nitrate
6. 6.MCAA, Chloroacetic acid
7. 7.BrO₃^-, Bromate
8. 8.Br^-, Bromide
9. 9.Cl^-, Chloride
10. 10.HSO₄^-, Hhydrogen sulfate
11. 11.S₂O₃^2-, Thiosulfate