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 10 6 –10 7 :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 HCl + 16 mM β‐alanine (β‐Ala) + 10% PVP + 2.86 mM N 2 H 4 ×2HCl, 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 HCl + 100 mM β‐Ala + 10% PVP + 2.86 mM N 2 H 4 ×2HCl, 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 2–3×10 −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.