Sensitive gas chromatographic-mass spectrometric method for the determination of gacyclidine in rat plasma and spinal cord dialyzates

A sensitive gas chromatographic-mass spectrometric (GC-MS) procedure is des cribed for the selective determination of gacyclidine (a non-competitive N- methyl-D-aspartate antagonist) in rat plasma and spinal cord dialyzates. It involves a single-step liquid-liquid extraction of plasma samples and dial yzates with hexane (pH 8.0) and the use of phencyclidine as an internal sta ndard. The compounds were separated on a GC capillary column and specifical ly detected by MS in the selected-ion monitoring mode. Gacyclidine and its internal standard were monitored by using the fragment ions at m/z 206 and 200, respectively. The method was accurate and reproducible (intra- and int er-day reproducibility < 12%) with a limit of quantification of 1.6 ng ml(- 1) using 100 mu l plasma of dialyzate samples. The calibration curves for r at plasma and Ringer's solution were linear (r(2) > 0.996) over a range fro m 1.6 to 200 ng ml(-1). The extraction efficiency was close to 100%. This s imple and rapid assay (total run time < 10 min) was validated for a pilot p harmacokinetic study in healthy rats after intravenous injection of a bolus dose of gacyclidine (2.5 mg kg(-1)).