Analysis of an Analgesic Mixture Utilizing a Nonporous Octadecylsilane Stationary Phase for Reversed-Phase Fast HPLC

A High Performance Liquid Chromatography (HPLC) method utilizing nonporous silica particle technology has been developed for the assay of an analgesic mixture containing aspirin, caffeine, and codeine. The separation and quantitation of the mixture was achieved on a column packed with nonporous silica particles chemically bonded with octadecylsilane (3.0 μm particles) using a mobile phase of 95:5 v/v 0.01 M phosphate buffer (pH 3.0)-methanol at a flow rate of 600 μL/min with UV detection at 216 nm. The separation was achieved within 3 min. The method showed linearity for aspirin in the range 40–242.5 μg/mL, and for caffeine and codeine in the range 7.5–45 μg/mL. Inter- and intra day precision ranged from 0.12–1.95% for aspirin, 0.07–.69% for caffeine, and 0.06–1.69% for codeine. The limits of detection for the analytes were 157 ng/mL for aspirin, 28 ng/mL for caffeine, and 30 ng/mL for codeine based on a signal-to-noise ratio (S/N) of 3 and a 10 μL injection.