Quantitation of levorphanol in human plasma at subnanogram per milliliter levels using capillary gas chromatography with electron-capture detection

A gas chromatographic method for the determination of levorphanol in human plasma is described. The method utilizes extractive alkylation with tetrabu tylammonium cation as the phase-transfer catalyst and pentafluorobenzyl bro mide as the alkylating agent, and employs a structural analog, d-3-hydroxy- N-ethylmorphinan, as the internal standard. The pentafluorobenzyl ethers fo rmed are separated by capillary gas chromatography and detected by electron capture. The method has good precision and accuracy for concentrations ran ging from 0.25 ng/ml to 100 ng/ml and has been used to measure plasma conce ntrations as part of a study to evaluate the management of chronic neuropat hic pain with levorphanol. (C) 1999 Elsevier Science B.V. All rights reserv ed.