[Study on reversed-phase ion-pair chromatographic determination of thiosulfate and iodide anions]

This paper describes an indirect reversed-phase ion-pair chromatographic separation and UV indirect photometric detection of and S2O3(2-) and I- by pre-column derivatization with Hg-EDTA to form their corresponding ternary complexes EDTA-Hg-S2O3 and EDTA-Hg-I for the first time. On a Zorbax ODS column with a mobile phase of methanol-water we have studied the influences of the ion-pair TBA+ concentration, pH value, the addition of EDTA, the concentration of organic modifier and ionic strength. In our experiments, the addition of EDTA had a notable effect on retention and peak shape. So the best chromatographic conditions are: methanol:water = 23:77 (V/V), the ion-pair reagent TBA+ 3.0 mmol/L, EDTA 1.0 mmol/L, NaNO3 2.0 mmol/L and buffer solution KH2PO4-Na2HPO4 (pH 7.0). The eluate is monitored by a UV detector operated at 254 nm and the detection limits of S2O3(2-) and I- are 61.1 ng and 37.6 ng respectively. Good linear relationships between the peak area (Y) and the amount of anion ions (X) with r = 0.9851 and 0.9892, respectively, are obtained. Interference of some ions is also studied. The method is both convenient and selective. It has already been used for the determination of I- in kelp and the results are satisfactory. The amount of I- in kelp is 0.0183%.