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Reversed-Phase High Performance Liquid Chromatography Coupled with Pulsed Electrochemical Detection for the Determination of Related Substances in Netilmicin Sulfate Injection

??OBJECTIVE To establish an improved reversed-phase high performance liquid chromatography method coupled with pulsed electrochemical detection for determining the related substances of netilmicin sulfate injection. METHODS Agilent Proshell 120 SB-C₁₈ column (4.6 mm×150 mm,2.7 μm)and gradient elution were used. Mobile phase A was 0.2 mol·L^-1 trifluoroacetic acid in 0.1 mol·L^-1 sodium hydroxide solution-acetonitrile (97:3), mobile phase B was 0.1% pentafluoropropionic acid-acetonitrile (97:3), and the flow rate was 0.8 mL·min^-1. A pulsed electrochemical detector was adopted, and the temperatures of detector and column were kept at 35 ??. The working electrode was a gold electrode with diameter of 3 mm and a quadruple-potential waveform (QPW)was selected as detection waveform. The injection volume was 25 μL. NaOH solution of 0.8 mol·L^-1 was added post-column at a flow rate of 0.3 mL·min^-1. RESULTS A total of 28 impurities could be detected and effective separation was achieved in the typical sample and most of which could not be separated in the method of Ch.P 2015. The linearity of the calibration curve for netilmicin ranged from 0.25 to 15 μg·mL^-1 with a coefficient of determination equal to 0.999 1. The LOD and LOQ of netilmicin were found to be 0.25 ng and 1.25 ng, respectively. The repeatability RSD(n=6) of the single largest impurity and total impurities were 0.9% and 0.8%, respectively. The sample solution was stable within 24 h. CONCLUSION Compared with previously published investigations, the improved method shows higher sensitivity, better separation ability and good reproducibility, especially for differentiating the origin of bulk drug for netilmicin sulfate injection, thus is more suitable for the determination of related substances of netilmicin sulfate injection.