high-performance liquid chromatographic determination of theophylline in human serum

a simple, rapid and sensitive hplc method for the determination of theophylline (t) in human serum has been developed. an isocratic system consisting of a /-l bondapak c18 column, mobile phase of methanol, phosphate buffer (22:78, ph=4.5), and a flow rate of 1.4 ml/min was used. the eluent was detected by uv at 275 nm at room temperature. 8-chlorotheophylline (8-ct) was used as an internal standard. the serum samples deproteinated by methanol containing 8-ct and the supernatant was injected into the hplc system. the retention times of 5.7 and 8.1 min were found for t and 8-ct, respectively. the linearity was checked in the range of 0.2- 30 µg/ml. relative standard deviation for both inter-day and intra-day precision analysis was less than 5%. no interference was observed from endogenous serum components. specificity was shown against some commonly co-administered drugs. simple and fast sample preparation, small sample volume (250 µl), precision, reproducibility, specificity, sensitivity and high percentage recovery (98 %) make the method to be practically useful for t monitoring in asthmatic patients.