Capillary Electrophoresis of Alkali and Alkaline-Earth Cations with Imidazole or Benzylamine Buffers

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Abstract
The separation of alkali, alkaline earth, and ammonium cations in several samples of water was achieved by capillary electrophoresis with indirect UV detection. A solution of imidazole (10−2 M, pH 4.5) was used as buffer to resolve a mixture of six cations (K+, Na+, Ca2+, Ba2+, Li+ and Mg2+) by capillary electrophoresis at 214 nm in less than 10 min. The addition of potassium cation to the running buffer has an influence on the resolution of Ca2+/Na+ and Na+/Mg2+ peaks. A linear relationship between the corrected peak area and concentration was obtained in the 1–10 ppm range for these cations using a hydrodynamic injector. This electrophoretic system permitted the separation of these inorganic cations at a 50 ppb-level concentration with an hydrodynamic injection, thus making it possible to quantitatively determine their presence in mineral waters by capillary electrophoresis. At pH 4.5, potassium and ammonium unfortunately have identical ionic mobilities causing them to comigrate in an imidazole buffer. Using an alkaline solution of benzylamine (10−2 M, pH 9) as carrier electrolyte, their separation can be successfully achieved with excellent resolution at 204 nm. The analyses of tap water and several mineral waters have been achieved by capillary electrophoresis.