Simultaneous quantitation of opioids in blood by GC–EI-MS analysis following deproteination, detautomerization of keto analytes, solid-phase extraction, and trimethylsilyl derivatization
Seven opioid analytes including codeine, morphine, 6-acetylmorphine, hydrocodone, hydromorphone, oxycodone, and oxymorphone were detected in postmortem blood (n > 1000). Two milliliters of specimen was deproteinated with ~ 2.5 mL of methanol and derivatized with hydroxylamine before solid-phase extraction and derivatization with BSTFA + 1% TMCS. Extracts were assayed by gas chromatography–electron impact-mass spectrometry utilizing selected ion mode. One-microliter aliquots were injected onto an HP-1MS capillary column (30 m x 0.25-mm i.d., 0.25 µm) with a helium linear velocity of 62 cm/s. Temperature programming began at 160°C (hold 0 min), then increased at rates of 35°C/min to 195°C, 5°C/min to 240°C, and 30°C/min to 300°C (hold 2 min) resulting in a total run time of 14-min. Quantitative determinations were based on the ratios of the analyte peak areas to the corresponding deuterated analogues. Calibration curves were linear for the following concentrations: 10–500 ng/mL (6-AM), 100–2000 ng/mL (oxycodone), and 50–1000 ng/mL (all other opioids). LOQs ranged from 5 ng/mL (6-AM) to 20 ng/mL (oxycodone). Between-run precision yielded CVs ranging from 2.79% to 5.34% (n = 12). These data suggest that methanolic deproteination and dual derivatization improve separation and simultaneous quantitation of seven opioid analytes in difficult matrices.