Determination of major metal cations in milk by capillary zone electrophoresis

A reliable and rapid capillary zone electrophoresis method for the determination of the major of cations in milk samples was developed. Sample preparation consisted of dilution, acidification to pH 4.0 with 1 mol L−1 acetic acid and filtration. The complete separation of K+, Ca2+, Na+ and Mg2+ could be achieved in 4 min with a simple electrolyte composed of 10 mmol L−1 imidazole and 1 mol L−1 acetic acid (pH 3.6). The running voltage was 25 kV at 25 °C. Indirect UV detection was achieved at 185 nm. Detection limits ranged from 0.06 to 0.57 mg L−1 and quantification limits ranged from 0.16 to 0.62 mg L−1. Precision data showed relative standard deviations (RSD%) lower than 4.1% for relative migration time and 2.4% for milk concentrations, respectively. Recoveries of cations in samples analysed ranged from 97.7% to 101.1%. Thirty samples of milk were analysed, obtaining mean values of 1.46, 1.19, 0.505 and 0.126 g L−1 for K+, Ca2+, Na+ and Mg2+, respectively.