RESUMEN
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 MGⅡ, 4.6 mm×250 mm,5 μm)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.