Determination of iodide and thiosulfate by paired-ion, reversed-phase high-performance liquid chromatography with ultraviolet absorbance, electrochemical, and conductimetric detection.

Inorganic anions are typically determined by ion chromatography, ion-selective electrodes, or by "wet chemical" procedures. An alternative to these approaches is afforded by paired-ion, reversed-phase high-performance liquid chromatography (HPLC), and the application of this technique to the determination of iodide and thiosulfate is discussed. Each analyte can be determined using ultraviolet (UV) absorbance detection and oxidative, amperometric electrochemical detection (ED). Furthermore, in the case of iodide, an additional and quite selective ED scheme is available through the use of series-configured dual glassy carbon electrodes. The dual-series ED approach utilizes an upstream electrode which is maintained at an oxidative potential. This results in the formation of an electroactive species, which may be detected at a downstream electrode held at a reductive potential. Finally, it is demonstrated that non-suppressed conductimetric detection is also perfectly viable within the context of paired-ion, reversed-phase HPLC, provided the overall conductance of the mobile phase is not excessive.