Separation and determination of cations in beverage products by capillary zone electrophoresis

Cation determination is important for quality control of beverage products. To determine a large group simultaneously, a capillary electrophoresis procedure is developed with indirect UV at 214 nm in a three-complex buffer system (10 mM N,N-dimethylbenzylamine (DBA), 8 mM lactic acid and 2 mM 18-crown-6) with good mobility matching with desired cations. Under optimized conditions with pH adjusted to 4.65, a baseline separation is achieved for 14 cations (Rb+, NH4+, K+, Ca2+, Na+, Mg2+, Mn2+, Co2+, Fe2+, Cd2+, Cr3+, Ni2+, Zn2+ and Cu2+) within 7 min using an uncoated silica column. To cover ng/l to μg/l range, both hydrostatic and electrokinetic sampling are studied, showing working ranges within (0.05–50)/(0.005–2) μg/l and detection limits (13–78)/(1.4–10) ng/l, respectively with satisfactory repeatability (RSD 0.31–0.47% for migration time, and 3.0–4.0% for peak height measurement). Agreeable results with established inductively coupled plasma-atomic emission spectrometry method have been obtained for orange juice and tea samples.