Previously, the Japanese Water Supply Act listed analysis of chlorate only in “Appendix No. 13: Simultaneous analysis by ion (anion) chromatography”.  However, from April 1^st 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 w/v% sodium thiosulfate 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.


Sample : 5 μL
10 μg/L each for ClO₃^-, BrO₃^-
in Tap water containing sodium thiosulfate 0.3 w/v%
1. ClO₃^-, Chlorate
2. BrO₃^-, Bromate
3. S₂O₃^2-, Thiosulfate

Sample: 5 μL
Tap water containing
sodium thiosulfate 0.3 w/v%
1. ClO₃^-, Chlorate
2. BrO₃^-, Bromate
3. S₂O₃^2-, Thiosulfate

Column       : Shodex RSpak JJ-50 2D (2.0 mm I.D. x 150 mm)
Eluent       : (A); 200 mM HCOONH4 aq./(B); CH3CN
               Linear gradient (High pressure);
               85 % B (0 min) → 85 % B (8 min) → 50 % B (9 min) → 50 % B (20 min)
Flow rate    : 0.3 mL/min
Detector     : ESI-MS/MS (MRM Negative) for ClO3-, BrO3-
               ESI-MS (SIM Negative) for S2O32-
Column temp. : 50 °C