Continuous-Flow Determination of Trace Iodine by Atmospheric-Pressure Helium Microwave-Induced Plasma Atomic Emission Spectrometry Using Generation of Volatile Iodine from Iodide

Abstract

A simple continuous-flow generation of volatile iodine by oxidation of aqueous iodide is described for the determination of low concentrations of iodine by atmospheric-pressure helium microwave-induced plasma atomic emission spectrometry (MIP-AES) in the normal ultraviolet (UV) 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 MIP source and the entrance slit of the monochromator have both been purged with nitrogen to minimize oxygen absorption below 190 nm. Iodine atomic emission lines at 206.16 and 183.04 nm have been selected as the analytical lines. Of various oxidation reactions examined, an oxidizing solution of 1.0 mM sodium nitrite in 5.0 M sulfuric acid is the most favorable for the generation of elemental iodine. The gaseous iodine is separated from the solution in a simple gas/liquid separator and swept into the helium stream of a microwave-induced plasma for analysis. The best attainable detection limits (3σ criterion) for iodine at 183.04 and 206.16 nm were 2.3 and 3.2 ng/mL, respectively, with the corresponding background equivalent concentrations of 60 and 118 ng/mL in iodine concentration. The typical analytical working graphs obtained under the optimized experimental conditions were rectilinear over approximately 4 and 3 orders of magnitude in concentration for the 206.16- and 183.04-nm iodine lines, respectively.