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Rapid Method for Analysis of Aspirin–Butalbital in Serum Utilizing a Monolithic C18 Column

Abstract A fast and sensitive high performance liquid chromatography (HPLC) assay was developed for the simultaneous determination of aspirin–butalbital in human serum. Serum samples were treated with a solid phase extraction procedure. The analytes were separated using a mobile phase of 90:10 (v/v) 0.1 M aqueous potassium phosphate monobasic (pH 4)‐acetonitrile on a monolithic C18 column with UV detection at 220 nm. Benzoic acid was used as the internal standard (IS). The method was validated over the range of 0.5–100 µg mL−1 for each drug. The method proved to be accurate (percent bias for all calibration samples varied from −13 to 6.6%) and precise (range from 0.1% to 10%). The mean percent absolute recoveries were 104 ± 6.3 for aspirin, 92.6 ± 5.5 for butalbital and 106 ± 6.9 for the internal standard. The assay should be applicable for use in pharmacokinetic studies and routine serum monitoring of these drugs.