Cost-efficient Use of Gas Chromatography–Mass Spectrometry: A “Piggyback” Method for Analysis of Gabapentin

Abstract

Mass spectrometry coupled with gas chromatography (GC/MS) is a powerful analytical tool combining analytical sensitivity and specificity. Its successful application to toxicology and in-born error testing is well known. In the current healthcare environment, clinical laboratories must identify means to reduce costs and improve productivity, including workstation consolidation (1) . This applies equally well to the utilization of specialized tools such as GC/MS, and the ability to maximize the productivity of a GC/MS set-up should enhance its economic value to the laboratory. We have had in use in our laboratory a GC/MS method for the measurement of methylmalonic acid (MMA) in plasma, based on solid phase anion-exchange extraction, derivatization with cyclohexanol, and separation with quantification using GC/MS (2) . Gabapentin (Neurontin) is a relatively new antiepileptic drug with a structure similar to the neurotransmitter γ-aminobutyric acid but containing a 6-carbon ring in place of the central methylene group of γ-aminobutyric acid (3)(4)(5) . Efficacy studies have reported patient serum gabapentin concentrations of 0.5–10.0 mg/L (3) . Gabapentin concentrations in serum have been measured using HPLC, gas chromatography, and capillary electrophoresis (6)(7)(8)(9) . Because both gabapentin and MMA are relatively small molecular weight organic acids, …