LIQUID-CHROMATOGRAPHY IN PHARMACEUTICAL ANALYSIS .11. DETERMINATION OF MUSCLE RELAXANT ANALGESIC MIXTURES USING REVERSED-PHASE AND ION-PAIR TECHNIQUES

High‐pressure liquid chromatography using reversed‐phase and/or ion‐pair techniques was used to optimize resolution of aspirin‐containing muscle relaxant mixtures as well as other therapeutic agents commonly found in muscle relaxant‐analgesic mixtures. The compounds were chromatographed on an octadecylsilane column using methanol‐water solvent systems, some of which contained tetrabutylammonium cation as counterion. Mixtures of methocarbamol‐aspirin and chlor‐zoxazone‐acetaminophen were selected to demonstrate separation and quantification. The methocarbamol‐aspirin mixture was chromatographed with methanol‐water (40:60, pH 6.8) containing 0.01 M tetrabutylammonium cation at a flow rate of 2.0 ml/min. The chlorzoxazone‐acetaminophen mixture was chromatographed with methanol‐water (50:50) at a 2.0‐ml/min flow rate. The separation and quantitation of each mixture were achieved in approximately 8 min with accuracy in the 2–3% range. Copyright © 1979 Wiley‐Liss, Inc., A Wiley Company