Capillary zone electrophoresis of inorganic anions with conductivity detection

Abstract

A carrier electrolyte system for capillary zone electrophoresis (CZE) resolving chloride, bromide, iodide, fluoride, nitrite, nitrate, sulfate, and phosphate in a hydrodynamically closed separation compartment is described. The carrier electrolyte combines the effects of pH, polyvinylpyrrolidone (PVP) and the counterionic constituent on the effective mobilities of the anions. In 300 μm ID capillary tubes made of fluorinated ethylene-propylene copolymer (FEP), and with detection of analytes with the aid of an alternating current conductivity detector, detection limits in the range of 3–10 ppb could be achieved for 200 nL sample volumes. The separation efficiencies were in the range of 1.5–2.5 × 10⁵ theoretical plates per meter for an adequate sample load. The reproducibility was evaluated for two concentration levels. For concentrations close to the limits of quantitation (50–120 ppb), the RSD values ranged from 1.5–12.6%, with the highest scatter for fluoride and phosphate. The RSD values were in the range of 0.4–1.5% for 300–1200 ppb concentrations of the anions. Typical analysis times were 2–5 min, depending on the anion species. A series of water samples (drinking, river, rain) was used to assess the practical applicability of the CZE method. The method is a suitable alternative for the determination of both anionic macro- and microconstituents in water with a good overall selectivity.