Potassium Bromate Assay by Redox Titrimetry Using Arsenic Trioxide

Bromate, a disinfectant, is one of the analytes of interest in wastewater analysis. Environmental laboratories have a regulatory need for their measurements to be traceable to NIST standards. Bromate is not currently certified as a NIST Standard Reference Material (SRM). Therefore, a traceable assay of potassium bromate (KBrO(3)) is needed. KBrO(3) was dissolved in water and assayed by redox titrimetry using arsenic trioxide (As(2)O(3)). A nominal (0.1 g) sample of As(2)O(3) was dissolved in 10 mL of 5 mol/L sodium hydroxide. The solution was acidified with hydrochloric acid and about 95 % of the KBrO(3) titrant was added gravimetrically. The end point was determined by addition of dilute (1:3) titrant using an automated titrator. The KBrO(3) assay was determined to be 99.76 % ± 0.20 %. The expanded uncertainty considered the titrations of three independently prepared KBrO(3) solutions.