Abstract: Objective To establish an on-line column switching high performance liquid chromatography method for determination of the main drugs in erythromycin ointment, and to recommend an effective means for quality control of related preparations. Methods The samples were extracted at 80 ℃ and injected directly. Under the column switching system, the samples were initially separated on a C₁₈ chromatographic column (50 mm×2.1 mm, 5 μm) before being transferred to a second C₁₈ column (150 mm×2.1 mm, 5 μm) for analysis after 2.5 min. The flow rate was 0.2 mL·min^-1 and the column temperature was 35 ℃. Results The linear relationship of erythromycin was good within the range of 1~100 μg·mL^-1 (r=0.999 4). The average recovery was 96.9%. Intraday and interday precision was less than 1.29% (n=6). Conclusion This study has improved the sample extraction method and completed the purification and enrichment of target components through on-line column switching. This method is simple, accurate, sensitive and stable, which can be used for content determination of erythromycin ointment.

Key words: erythromycin ointment, online column switching, high performance liquid chromatography, rapid extraction, content determination