Determination of chloride ions by reaction with mercury thiocyanate in the absence of iron(III) using a UV-photometric, flow injection method

Abstract

The absorbance at 254 nm of a previously undocumented complex, which forms when chloride and mercury thiocyanate are mixed in aqueous solution, provides the basis for a new technique for the determination of chloride ions in water. Performance of this new technique is compared to that of the widely applied method described by Utsumi, in which Fe^III is included as a reagent and the absorbance of the absorbing species, Fe(SCN)²⁺, is measured at 450 nm. A single-line flow injection (FI) system was employed for studies of the Cl^–Hg(SCN)₂ system at 254 nm. A logarithmic response was obtained for chloride concentrations in the range of 0–2000 µg ml^–1 without the need for sample dilution. The detection limit of the system was determined to be 0.16 µg ml^–1. Sulfate, magnesium, and calcium ions do not interfere with chloride ion determination. Bromide and iodide ions interfere significantly in the determination of Cl^– over the concentration ranges of 10–100 µg ml^–1 of interferent.