Differential-pulse stripping voltammetry for the determination of soluble iron in simulated PWR coolant

A method has been developed for the determination of dissolved or ionic iron in pressurised water reactor (PWR) coolant using differential-pulse voltammetric stripping (DPVS) following adsorptive accumulation of an iron(III)-catechol complex at a hanging mercury drop electrode. The method does not discriminate between Fe(II) and Fe(III) ions and the total ionic iron is determined in a Tris buffered solution at pH 8 ± 0.1. Interference from the reaction of boric acid in the coolant with the catechol was overcome by limiting the total boron in the analytical solution to ⩽ 100 mg l–1 and adding mannitol. No interference was observed from ions of common transition metals such as copper, nickel, cobalt and manganese. The effects of pH, catechol concentration, accumulation voltage and time were investigated in simulated coolant solution. The limit of detection was of the order of 0.1 µg l–1 and the precision of a single determination based on a standard additions procedure was considered to be in the range 10–15%.When the results obtained by this technique were compared with those obtained by a spectrophotometric method, good agreement was obtained. The DPVS method for the determination of ionic iron in PWR should prove valuable in corrosion studies and it can complement alternative methods, such as electrothermal atomic absorption, which only gives the total iron in solution.