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Determination of Related Substances of Azithromycin for Injection by Gradient RP-HPLC

??OBJECTIVE To establish a gradient elution method for determination of related substances of azithromycin for injection. METHODS Gradient elution was used for the analysis. A C₁₈ (CAPCELL PAK MG??, 4.6 mm??250 mm,5 ??m)column was used. The mobile phase A consisted of 0.05 mol??L^-1 K₂HPO₄ solution (pH 8.2, adjusted with 20% phosphoric acid)-acetonitrile (45??55), and the mobile phase B was methanol. The flow rate was 1.2 mL??min^-1, and the detection wavelength was set at 210 nm. The column temperature was maintained at 30 ??. The gradient elution program was as follows: 0-35 min, A:75%??95%; 35-64 min, A:75%; 64-65 min, A:95%??75%; 65-71 min, A:75%. RESULTS Azithromycin, near peaks and known impurities were well separated from each other. All acid radicals of azithromycin for injection did not influence the determination of related substances of azithromycin. CONCLUSION This method is more specific than the exising method for determination of related substances of azithromycin, which can more effectively control the quality of the drug.