Determination of fentanyl in whole blood at subnanogram concentrations by dual capillary column gas chromatography with nitrogen sensitive detectors and gas chromatography/mass spectrometry.

Two methods for the determination of fentanyl at subnanogram concentrations in whole blood have been developed and evaluated. The initial screening was by gas chromatography with nitrogen sensitive detection (GC/NPD) in a splitless injection onto two fused-silica, 0.32-mm i.d. capillary columns (5% and 50% phenyl methyl silicone). Confirmation was by gas chromatography/mass spectrometry (GC/MS) using selected ion monitoring of a splitless injection onto a 0.1-mm i.d., 0.34-microns 5% phenyl methyl silicone capillary column. The methods were studied at fentanyl concentrations over the range 0.05 to 5.0 ng/mL using 2 mL of blood. The detection limits were set at 0.10 ng/mL for GC/NPD and 0.05 ng/mL for GC/MS. The overall recovery of fentanyl was found to be greater than 75% over the range of 0.25 to 2.5 ng/mL. The within-run precision determined at fentanyl concentrations of 0.25 and 1.0 ng/mL showed coefficients of variation ranging from 8.7 to 14.8%. The between-run precision determined at concentrations of 0.4 and 0.8 ng/mL showed coefficients of variation ranging from 3.3 to 11.6%. The blood calibration curves in the range of 0.25 to 2.5 ng/mL monitored over a 3-month period showed a mean correlation coefficient of 0.99 for both the GC/NPD and GC/MS methods.