Rapid quantification of urinary oxycodone and oxymorphone using fast gas chromatography-mass spectrometry

Human urine specimens that were determined to be presumptively positive for oxycodone and its metabolite, oxymorphone, by immunoassay screening were assayed using fast gas chromatography-mass spectrometry to positively identify and quantify the oxycodone and oxymorphone present. Urine specimens were first spiked with deuterated internal standards, oxycodone-d(3) and oxymorphone-d(3), subjected to acid hydrolysis, and then extracted using a positive-pressure manifold and mixed-bed solid-phase cartridge extraction methodology. Extracts were derivatized using methoxylamine and acetic anhydride. The acetylated-oxime derivatives of oxycodone and oxymorphone were identified and quantified using a selective ion monitoring (SIM). The method was found to be linear for both analytes to 1600 ng/mL, and limits of detection for oxycodone and oxymorphone were found to be 40 ng/mL and 20 ng/mL, respectively. Interlaboratory data comparisons (n = 40) showed correlation coefficients of 0.9999 and 0.9997 for oxycodone and oxymorphone, respectively. Twelve semisynthetic, structurally similar compounds at concentrations of 5000 ng/mL were assayed in the presence of oxycodone and oxymorphone and found not to interfere with identification and quantitation by this method. Finally, exact mass and tandem mass spectrometry techniques were employed to elucidate the structures of the SIM ions.