OBJECTIVETo establish a method for the determination of gypsum and magnesium in decoction by capillary zone electrophoresis and study the influence of different compatibility on the contents of calcium and magnesium dissolution.

METHODNine decoctions with gypsum were prepared and analysed by L9 (3(4)) orthogonal design and the contents of calcium and magnesium ions were determined by the set method. The conditions of the experiment were a running buffer of 6.4 mmol x L(-1) imidazole solution (glacial acetic acid ajusted pH to 3.50) and an applied voltage of 10 kV (room temperature). Samples were introduced by hydrodynamic injection (8 cm x 7 s) and determined with on-column UV monitoring at 214 nm. Copper sulphate was chosen as the internal standard.

RESULTSThe linear responses covered the range from 0.009 68 mg x L(-1) to 9.68 mg x L(-1) (r = 0.998 1) for calcium, the detection limits (S/N = 3) and the quantitation limits (S/N = 10) of calcium were shown to be 0.002 1 mg x L(-1) and 0.007 1 mg x L(-1), respectively. The average recovery for calcium was 100.4%. The linear response covered the range from 0.01 mg x L(-1) to 10 mg x L(-1) (r = 0.995 9) for magnesium. The detection limits (S/N = 3) and the quantitation limits (S/N = 10) of magnesium showed to be 0.002 8 mg x L(-1) and 0.008 9 mg x L(-1), respectively. The average recovery for magnesium was 96.4%.

CONCLUSIONThe method is simple, rapid, cost-effective and precise with satisfactory results. The influence of Ephedra and Semen Armeniacae Amarum on the contents of gypsum dissolution are significant, while that of Radix Glycyrrhizae on the contents of gypsum dissolution is insignificant. The influence of Ephedra on the contents of magnesium dissolution are significant, while that of Semen Armeniacae Amarum and Radix Glycyrrhizae on the contents of magnesium dissolution are insignificant.