Factors affecting the amperometric determination of trace quantities of total residual chlorine in sea water

Abstract

The standard scheme for the determination of total residual chlorine in seawater by amperometric titration is not suitable for many recent studies that require lower and lower detection limits (<0.1 mg L/sup -1/ or <1.4 ..mu..equiv L/sup -1/). The interference of iodate that originated from the reaction between iodide and hypobromite and from naturally occurring iodate in seawater may yield variable blank and/or grossly underestimated results. The pH chosen in the present analytical scheme is at a value where the reaction between iodate and iodide is sluggish and the extent to which iodate is converted to triiodide is most sensitive to small pH changes. A titration at pH 2 will yield the true concentrations of total residual chlorine after the contribution from naturally occurring iodate is corrected for. The interference from nitrite should be considered if a submilligram per liter level of residual chlorine is to be measured and/or if the titration is carried out at a pH below 3. This interference may be removed by the addition of sulfamic acid.