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Optimized Method for Determination of Gabapentin in Serum by High‐Performance Liquid Chromatography

The anticonvulsant drug gabapentin and its heptaneacetic acid analog—used here as an internal standard—are isolated from serum (pH 9) with an octyldecyl (C-18) solid-phase sorbent column. To enhance analytical detection, trinitrobenzene derivatives of these extracted compounds are prepared quickly within 10 min. To furthur improve chromatographic selectivity, the derivatives are concentrated on a thin C-18 solid-phase membrane and interferences are washed away. The retained purified derivatives are eluted from the membrane with a small volume of solvent and the eluate is directly injected onto an Ultrasphere C-18 high-performance 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 coefficients of variation (CV) range from 2.3 to 2.9% through the concentration range 0.5–4.0 mg/L. To illustrate the rationale for selection of test parameters for a robust method, we present optimization graphs for these processes. Moreover, we discuss the advantage of the packed cartridge and membrane sorbents as companion extraction devices.