A novel buffer system for separation of metal cations by capillary electrophoresis with indirect UV detection

Generally, the buffers used for metal ion separations in capillary electrophoresis (CE) consist of a UV-active substance, pH-adjuster, and weak complexing reagent. This paper describes the successful separation of metal ions with a new buffer that contains no complexing reagent. Of several weakly basic compounds tested, 2-aminopyridine was selected as the most useful UV-active substance. It was used at a concentration of 15 mM with pH adjusted to 5.0 +/- 0.1 by acetic acid. The degree of protonation of the UV-active substance played an important role in detection. The stacking phenomenon was a significant contributor to efficiency in this buffer system, and water-diluted samples gave especially high efficiencies. When a 75-micron-i.d. fused-silica capillary was used, a separation efficiency of 1.8 x 10(5) was observed. Quantitative determinations of Ca2+, Mn2+, Zn2+, and Cd2+ were achieved with good linear calibration curves over the range of concentration from a few milligrams per liter to 100 mg/L. The detection limits were 0.2 mg/L for Ca2+, 0.4 mg/L for Mn2+ and Zn2+, and 0.6 mg/L for Cd2+, based on three times the baseline noise.