An Automated, Column-Switching HPLC Method for Analyzing Active and Excipient Materials in Both Cream and Ointment Formulations

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Abstract
We developed a microprocessor-controlled, tandem reverse-phase HPLC method for analyzing both cream and ointment formulations. Analytes included: a developmental corticosteroid in both cream and ointment formulations; a developmental naphthohydroquinone diester in the ointment; and benzyl alcohol, a cream excipient material. Sample preparation consisted simply of dissolving cream or ointment in 30:60 tetrahydrofuran:isopropanol, centrifuging to sediment undissolved residue, and directly injecting onto the HPLC column. With automated switching valves operating in a front-cutting mode, analytes plus internal standard were directed from the reverse-phase precolumn to a 30-cm reverse-phase analytical column while retained excipient materials were backflushed to waste. For comparison, we also analyzed the corticosteroid cream and ointment formulations by reverse-phase HPLC with conventional liquid-liquid partition sample preparation procedures. In all cases, method performance was satisfactory as evidenced by: sample recovery, response linearity, precision, stability specificity, peak tailing factors, peak assymetries, peak resolution, and theoretical plate counts. Compared with liquidated extraction techniques, the reported column-switching methods reduced required sample preparation times by a factor of nearly 3.