Analyte volatilization procedure for the determination of low concentrations of iodine by inductively coupled plasma atomic emission spectrometry. Invited lecture

Abstract

A simple method is described for the generation of a continuous flow of volatile iodine by the oxidation of aqueous iodide for the determination of low concentrations of iodine by inductively coupled plasma (ICP) atomic emission spectrometry in the normal ultraviolet and vacuum ultraviolet (VUV) regions of the spectrum. For measuring spectral lines in the VUV region, the monochromator and the enclosed external optical path between the ICP source and the entrance slit of the monochromator were both purged with nitrogen to minimize light absorption by atmospheric oxygen. The iodine atom emission lines at 178.28, 183.04 and 206.16 nm were selected as the analytical lines of interest. Of the various oxidation reactions investigated, an oxidizing solution of 5.0 mmol l^–1 of sodium nitrite in 8.0 mol l^–1 sulfuric acid was found to be the most appropriate for the generation of elemental iodine. The gaseous iodine is separated from the solution in a simple gas–liquid separator and swept into the argon stream of an ICP for analysis. The best attainable detection limits (3σ criterion) for iodine at 178.28, 183.04 and 206.16 nm were found to be 0.39, 0.55 and 2.1 ng ml^–1, respectively. Typical calibration graphs obtained under the optimized experimental conditions are rectilinear over approximately four orders of magnitude of concentration. The present method has successfully been applied to the determination of total iodine (i.e., iodide + iodate) in several brine samples.