Application of ion-exchange chromatography with an ion-selective electrode detector to iodine determination in natural waters

A system is described which uses a selective electrode for potentiometric detection of anions in natural waters after ion-exchange separation. With an iodide-selective electrode in the flow cell, a linear relationship exists between iodide concentration and potential in the sub-Nernstian range (0–100 μM). The limit of detection is 0.015 μM for an injection of 125 μl of sample. For optimum electrode performance, a constant iodide background of about 0.5 μM is required in the column effluent passing through the detector. This background is added uniformly through a short section of hollow-fibre dialysis tubing in a concentric-flow diffusion cell. The detector also responds to other anions which affect the solubility of silver ion. This can be used to advantage if chromatographic separation is sufficient. Preconcentration of iodide in fresh waters on an anion guard cartridge allows determination down to 1 nM concentrations. For sea-water samples, simple chemical pretreatment permits quantitation of different iodine species.