Rapid capillary zone electrophoresis method for the determination of metal cations in beverages

A rapid and reliable capillary zone electrophoresis method for the determination of inorganic cations was developed. The complete separation of K⁺, Ba²⁺, Ca²⁺, Na⁺, Mg²⁺, Mn²⁺, Ni²⁺, Cd²⁺, Li⁺ and Cu²⁺ can be achieved in 4 min with a simple electrolyte composed by 10 mM imidazole as the carrier buffer and background absorbance provider and acetic acid as the complexing agent (pH 3.60). Injection was performed hydrostatically by elevating the sample at 10 cm for 30 s. The running voltage was +25 kV at room temperature. Indirect UV-absorption detection was achieved at 185 nm. The detection limit was in the range between 0.06 mg/l (Mg²⁺) and 0.57 mg/l (K⁺) and the quantification limits ranged from 0.10 mg/l (Ni²⁺) to 0.80 mg/l (Cu²⁺). The calibration graphs were linear in the concentration range from the quantification limit till at least 1 g/l in K⁺, 10 mg/l in Ba²⁺, Ca²⁺, Mg²⁺, Mn²⁺, Ni²⁺ and Cd²⁺, 40 mg/l in Na⁺ and 12 mg/l in Li⁺ and Cu²⁺. The repeatability, intraday and interday analysis were ≤1.55% and ≤3.64% for migration time and ≤3.38% and ≤3.63% for peak area. The method developed has been applied to several beverage samples with only a simple dilution and filtration treatment of the sample. The proposed method is simple, fast, cheap and it is achieved with common products in either laboratory. For these reasons, it is a very useful method for routine analysis.