Determination of trace iodide in seawater by capillary electrophoresis following transient isotachophoretic preconcentration: Comparison with ion chromatography

Abstract

Usefulness of capillary electrophoresis (CE) in combination with transient isotachophoresis (tITP) as on-line preconcentration technique was examined for routine analysis of trace iodide in seawater. The combined method was based on an electrolyte system where 0.5 mol l −1 sodium chloride and 25 mmol l −1 cetyltrimethylammonium chloride at an acidic pH and 0.5 mol l −1 2-( N-morpholino)ethanesulfonate (pH 6.0) served as carrier and terminating electrolyte, respectively. Under optimized tITP-CE conditions (a carrier electrolyte pH of 2.4), the peak of 1 μg l −1 iodide in artificial seawater can be clearly detected at 226 nm, with the detection limit as low as 0.2 μg l −1. Calibration curve was linear in the range of 0–40 μg l −1 ( n=10; regression coefficient = 0.99992). Relative standard deviation values of the migration time, peak height and area of surface seawater iodide (0.6, 3.1 and 1.5%, respectively) proved an excellent run-to-run reproducibility performance of the proposed method. The method was applied to seawater samples containing sub- and low-μg l −1 levels of iodide, and the results obtained agreed well with ion chromatographic data. Detection of nitrate and nitrite was also possible in the same tITP-CE run (limits of detection 25 and 20 μg l −1, respectively, at 210 nm). The analytical characteristics of the method were discussed in comparison with an ion chromatographic procedure previously developed in authors’ laboratory.