Prior to use the capillary was pretreated daily with 1 mol 1-~ NaOH for 5 min, then rinsed with deionized water for 2 min. In order to obtain stable electropherograms in terms of baseline noise, the capillary was rinsed successively with 0.1 mol 1 -I HC1 (0.2 rain), deionized water (0.3 min) and carrier electrolyte (1.4 min) before each sample injection.