ABSTRACT
OBJECTIVE: To establish an improved LG method combined with pulsed electrochemical detection for the analysis of etimicin sulfate. METHODS: The mobile phase was composed of 40 mL of acetonitrile and 960 mL of an aqueous solution containing 15 mL · L-1 of trifluoroacetic acid, 500 μL · L-1 of pentafluoropropionic acid, 8 mL · L-1 of sodium hydroxide (50%) and 1.5 g · L-1 of sodium sulfate. The pH of the aqueous solution was adjusted to 3.5 with 50% NaOH solution. A pulsed electrochemical detector, which was kept at 35 C in a hot air oven was adopted. The electrochemical cell consisted of a working electrode, a pH-Ag/AgCl reference electrode and a titanium counter electrode. The working electrode was a gold electrode (diameter 3 mm) and a quadruple-potential waveform (QPW) was selected as detection waveform. The 0.8 mol · L-1 NaOH solution was added post column at a flow rate of 0.4 mL · min-1. RESULTS In total, 22 impurities could be separated. The LOD and LOQ of etimicin were found to be 2 ng and 6 ng respectively. The linearity of the calibration curve for etimicin ranged from 0.24 to 45 μg · mL-1 with a coefficient of correlation equal to 0.9997. The repeatability RSDs (n=6) of the content and total impurities in one sample were 0.7% and 1.72% respectively. The inter-day repeatability RSDs (n=18) of the content and total impurities in one sample were 0.98% and 1.71% respectively. The sample solution was stable within 12 h. CONCLUSION: Compared with previously published methods, this improved method shows higher sensitivity, better separation ability and robustness and has been incorporated by the Chinese Pharmacopoeia (Ch. P.) 2015 for analysis of etimicin sulfate.