Methoxyacetylfentanyl

The run buffer used for opioid and synthetic opioid separations was 12 mmol/L acetic acid, 3.3 mmol/L ammonium acetate pH 4.4 (Sigma-Aldrich, St. Louis, MO, USA) in ultrapure water (Millipore Milli-Q, 18.0 MΩ-cm). Acetaminophen, caffeine, mannitol, procaine, quinine, and methanol were all purchased from Sigma-Aldrich (St. Louis, MO, USA).
All fentanyl analogues (acetyl fentanyl, acryl fentanyl, benzyl fentanyl, butyryl fentanyl, furanyl fentanyl, methacryl fentanyl, methoxyacetyl fentanyl, phenyl fentanyl, valeryl fentanyl) were purchased as hydrochloride salts from Cayman Chemical (Ann Arbor, MI, USA) or, when possible, as 1 mg·mL⁻¹ methanolic solutions. Powdered standards and samples were dissolved gravimetrically in methanol (Sigma-Aldrich, St. Louis, MO). The remaining opioids and narcotics (heroin, fentanyl, cocaine, U-47700) were purchased as 1 mg·mL⁻¹ solutions in methanol or acetonitrile from Cerilliant (Round Rock, TX, USA). All sample dilutions were prepared in run buffer, and methanol was added as necessary to allow for a constant 4 % by volume organic solvent across all analyses. When increased analyte concentrations were desired, standards were concentrated to assure each sample contained a maximum of 4 % (v/v) solvent.