Extraction and quantitation of carfentanil and naltrexone in goat plasma with liquid chromatography–mass spectrometry

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 μl of 1 M NaOH and extracted 2× with 2 ml of toluene. The extractions were combined and dried under N2 at 40 °C in a H2O bath. 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 (pH=4.4) 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.