Journal of Chromatography B, 793 (2003) 351–355 www.elsevier.com / locate / chromb Extraction and quantitation of carfentanil and naltrexone in goat plasma with liquid chromatography–mass spectrometry a, a b b * Robert P. Hunter , David E. Koch , Adrian Mutlow , Ramiro Isaza a Zoological Pharmacology Laboratory, Department of Anatomy and Physiology, Kansas State University, 129 Coles Hall, Manhattan, KS 66506-5802, USA b Department of Clinical Sciences, Kansas State University, Manhattan, KS 66506, USA Received 25 November 2002; received in revised form 16 April 2003; accepted 16 April 2003 Abstract This method is the first analytical method for the detection and quantitation of carfentanil and naltrexone at clinically relevant concentrations using liquid chromatography–mass spectrometry. Samples were alkalinized with 100 ml of 1 M NaOH and extracted 23 with 2 ml of toluene. The extractions were combined and dried under N at 40 8C in a H O bath. 2 2 Chromatography was performed using a Zirchrom PBD column and a mobile phase of 30:70 acetonitrile / 10 mM ammonium acetate and 0.1 mM citrate (pH54.4) at a flow rate of 0.3 ml/min. The lower limit of quantitation was 8.5 pg/ml for carfentanil and 0.21 ng / ml for naltrexone.  2003 Elsevier B.V. All rights reserved. Keywords: Carfentanil; Naltrexone 1. Introduction species [3]. Carfentanil is a synthetic derivative of fentanyl ( Fig. 1). In most situations, CARF anes- Carfentanil (CARF) is the most potent opioid thesia is reversed using the antagonist naltrexone agonist currently in use. It is 203 more potent than (NLT) [1]. fentanyl [1], and is approved by the United States Several studies of CARF have been reported in Food and Drug Administration for immobilization of both domestic [4,5] and non-domestic animals [6,7] free-ranging or confined members of the family but the pharmacokinetics and tissue residues of Cervidae (i.e., white-tailed deer, elk, and moose). CARF are unknown. Due to the extremely potent Since its development in 1975, CARF has become nature of CARF, very low concentrations of CARF the drug of choice for immobilization of a wide are believed to be achieved in the blood and it has variety of non-domestic mammals [1,2], because it not been previously possible to accurately measure allows for rapid and reliable induction of anesthesia the low concentrations of CARF in plasma. While with small volumes of CARF in a diverse range of there is a semi-commercial ELISA assay available, the limit of quantitation is 1 ng / ml [8]. The use of liquid chromatography–mass spectrometry (LC– *Corresponding author. Tel.: 11-785-532-4524; fax: 11-785- MS) will allow for the determination of plasma 532-4557. E-mail address: rhunter@vet.ksu.edu (R.P. Hunter). levels of CARF prior to and following reversal of 1570-0232 / 03 / $ – see front matter  2003 Elsevier B.V. All rights reserved. doi:10.1016 / S1570-0232(03)00351-9