OPTIMIZED METHOD FOR DETERMINATION OF GABAPENTIN IN SERUM BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

The anticonvulsant drug gabapentin and its heptaneacetic acid analog-u sed here as an internal standard-are isolated from serum (pH 9) with a n octyldecyl (C-18) solid-phase sorbent column. To enhance analytical detection, trinitrobenzene derivatives of these extracted compounds ar e prepared quickly within 10 min. To furthur improve chromatographic s electivity, the derivatives are concentrated on a thin C-18 solid-phas e membrane and interferences are washed away. The retained purified de rivatives are eluted from the membrane with a small volume of solvent and the eluate is directly injected onto an Ultrasphere C-18 high-perf ormance liquid chromatography column with quantification at 340 nm. No evaporation-concentration steps are necessary, Recoveries (extraction ) of gabapentin and the internal standard are 94.2 +/- 2.9% and 98 +/- 2.0%, respectively. Analytical responses are linear from lower limit of sensitivity of 0.05 mg/L up to at least 10 mg/L. Between-run coeffi cients of variation (CV) range from 2.3 to 2.9% through the concentrat ion range 0.5-4.0 mg/L. To illustrate the rationale for selection of t est parameters for a robust method, we present optimization graphs for these processes. Moreover, we discuss the advantage of the packed car tridge and membrane sorbents as companion extraction devices.