Trace-level determination of bromate in water by ion chromatography with optimised post-column derivatisation and UV/vis detection as triiodide
Bromate is generated by the oxidation of bromide traces during water disinfection, for example by ozonisation.
The US Environmental Protection Agency (US EPA) and the European Union (EU) currently prescribe a maximum bromate concentration of ten parts per billion (ppb) in drinking water.
For mineral waters the pertinent regulations stipulate a limit of 3ppb.
Bromate can be determined at trace levels by anion-exchange chromatography followed by post-column derivatisation with subsequent UV detection, according to US EPA Method 326.
The straightforward set-up uses a sulphuric acid eluent with catalytic amounts of ammonium molybdate and requires neither suppression nor sample preparation steps.
The bromate response was neither dependent on the investigated reaction temperatures (25-80C) nor on the examined iodide concentrations (0.26-0.75 mol/L KI).
In contrast, the molybdate and sulphuric acid concentrations had a significant influence on method sensitivity.
Increasing sulphuric acid concentrations (>31mmol/L) improved sensitivity and shifted the bromate peak to shorter retention times.
Ammonium molybdate concentrations of 45 and 90mol/L in the eluent yielded the best results.
Applying the optimum conditions for the triiodide method, a detection limit for bromate of less than 50ng/L (=50ppt) is achieved.
