SENSITIVE AND SELECTIVE ASSAY FOR FENTANYL USING GAS-CHROMATOGRAPHY WITH MASS-SELECTIVE DETECTION

A modified gas chromatographic assay, using mass-selective detection, has been developed for the quantitation of fentanyl in swine serum. Fe ntanyl and sufentanil, the internal standard, were extracted using a s ingle-step liquid-liquid extraction with dichloromethane. Sensitivity and selectivity were improved by using electron-impact ionization (EI) in the selected-ion monitoring (SIM) mode, where fentanyl and sufenta nil were monitored using the fragment ions at m/z 245 and 289, respect ively. The limit of quantitation (LOQ) is 0.05 ng/ml, using 1 ml of sa mple, with a C.V. of 10.8% and a signal-to-noise ratio of 29. Standard curves were linear (r(2) = 0.999) over the working range of 0.05-1.5 ng/ml, using 1/y(2) as a weighting factor. Recoveries averaged 69.8 +/ - 4.7%, 91.0 +/- 13.0% and 90.9 +/- 10.3% at serum concentrations of 1 .5, 0.5 and 0.1 ng/ml, respectively. Intra- and inter-day variances, w ere <12% at 0.1 ng/ml, and <10% at concentrations of 0.5, 1 and 1.5 ng /ml. Bias was 6.2% at the LOQ and less than or equal to 12.8% at every other standard curve concentration. Applicability of the assay is dem onstrated for the pharmacokinetic study of transdermally administered fentanyl in a postoperative swine.