Capillary electrophoresis determination of butalbital from serum using solid phase extraction (SPE) and ultraviolet detection

Butalbital is a sedative hypnotic that is used mainly in combination with a nalgesics in the treatment of tension headaches. This paper develops and va lidates a rapid and sensitive method for the determination of butalbital in serum using capillary electrophoresis (CE) and ultraviolet detection. The internal standard chosen for this assay was aprobarbital because it showed similar chemical structure, identical chromatographic/SPE characteristics, and was commercially available. The CE run buffer contained 50 mM sodium di hydrogen phosphate buffer at pH 9.0 containing 20 mM hydroxypropyl-beta-cyc lodextrin as a capillary zone electrophoresis (CZE) buffer additive. An SPE method, using C-18 Bond-Elut cartridges, was developed to recover th e drug and internal standard from serum. The CE system consists of a 75 mic ron I.D., 52 cm length fused silica capillary maintained at a run voltage o f 15 kV with sample detection performed at 254 nm. The limit of detection f or butalbital was < l mu g/mL from serum. Linear calibration curves generat ed in the concentration ranges of 1 to 60 mu g/mL showed a coefficient of d etermination greater than 0.99. The precision and accuracy of the method ca lculated as RSD and error were 0.65-3.16% and 2.20-8.90%, respectively. But albital is commonly coadminisetred with aspirin, acetaminophen, caffeine, a nd codeine for the treatment of tension headaches. The CE method baseline r esolved these compounds from the butalbital and the internal standard. Ther efore, there is a decreased chance for interference from commonly coadminis tered compounds in this assay.