Assay for the simultaneous determination of acetaminophen-caffeine-butalbital in human serum using a monolithic column.

A fast and sensitive high performance liquid chromatography (HPLC) assay was developed on a C18 monolithic column for the simultaneous determination of acetaminophen-caffeine-butalbital in human serum. Serum samples were treated with a solid phase extraction procedure. The analytes were separated using a mobile phase of 95:5 (v/v) 0.1M potassium phosphate monobasic (pH 2.41)-acetonitrile on the C18 monolithic column with detection at 220 nm. Benzoic acid was used as the internal standard (IS). The method was validated over the range of 1.25-100 microg/ml for each drug and found to be linear (r > 0.995, n = 12) with RSD less than 8.3%. The method proved to be accurate (percent bias for all calibration samples varied from -14.6 to -1.3%) and precise (ranged from 2.9 to 13.4%). The mean percent absolute recoveries from serum were 89.7 +/- 3.6 for acetaminophen, 95.5 +/- 4.5 for caffeine, 99 +/- 5.2 for butalbital and 83.4 +/- 3.9% for the internal standard.