Separation and determination of inorganic cations in beverages by capillary electrophoresis with indirect UV detection

A rapid, simple and reliable capillary electrophoresis method for the separation and quantitation of inorganic cations with indirect UV detection at 214 nm was developed. The electrolyte was: 12 mM imidazole as background absorbance provider; 5 mM malic acid and 1.0 mM 18-crown-6 ether as complexing agents; and 20% D₂O (v/v) to improve ion mobility. The pH was 4.25. The applied voltage was 22 kV at 22°C. Nine ions were completely separated and determined with correlation coefficients of 0.9979-0.9992. The relative standard deviations (RSD) were less than 0.5% for migration time and less than 5.2% for peak area (n=8). The detection limits (S/N=3) were from 0.08 mg L⁻¹ (for Na⁺) to 0.51 mg L⁻¹ (for Cu²⁺). To assess the reliability atomic absorption (AA) was also used to determine the same samples. Satisfactory results were obtained for real samples of jasmine tea drink and coconut milk.