Fig. 2

A typical chromatogram of standard drug mixture samples. Chromatographic conditions were acetonitrile-0.05 mol·L⁻¹ potassium dihydrogen phosphate (36: 64, v/v); the buffer pH was varied. a. pH 3.0; b. pH 3.5; c. pH 4.0; d. pH 4.5; e. pH 5.0