Determination of iodide in samples with complex matrices by hyphenation of capillary isotachophoresis and zone electrophoresis

A method has been developed for the determination of iodide in mineral water, seawater, cooking salt, serum, and urine based on hyphenation of capillary ITP and zone electrophoresis. A commercially available instrumentation for capillary ITP with column-switching system was used. ITP served for removal of chloride present in the analyzed samples in a ratio of 106-107:1 to iodide, zone electrophoresis was used for evaluation. Isotachophoretic separation proceeded in a capillary made of fluorinated ethylene-propylene copolymer of 0.8 mm id and 90 mm total length to the bifurcation point filled with a leading electrolyte (LE) composed of 8 mM HC1 + 16 mM β-alanine (β-A1a) + 10% PVP + 2.86 mM N 2 H 4 x 2HC1, pH 3.2; and a terminating electrolyte composed of 8 mM H 3 PO 4 + 16 mM β-Ala + 10% PVP + 5 mM N 2 H 4 , pH 3.85 for all the matrices except seawater. For ITP of seawater the LE consisted of 50 mM HC1 + 100 mM β-Ala + 10% PVP + 2.86 mM N 2 H 4 x 2HC1, pH 3.52. Distance of conductivity detector from the injection point and bifurcation point was 52 and 38 mm, respectively. Zone electrophoresis was performed in a capillary made of fused silica of 0.3 mm id and 160 mm total length filled with LE from isotachophoretic step. LODs reached for all matrices were 2-3 x 10 -8 M concentration (2.5-4 μg/L) enabled monitoring of iodide in all analyzed samples with RSD 0.4-9.3%. Estimated concentrations of iodide in individual matrices were 10 -6 -10 -8 M.