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