Chromasolv grade methanol and water

Standards for the screening and quantitation studies were obtained from either Cayman Chemical (Ann Arbor, MI), Cerilliant (Round Rock, TX), or Sigma-Aldrich (St. Louis, MO) as 1 mg mL⁻¹ standards in methanol or acetonitrile (when possible) or as pure crystalline material. Chromasolv-grade methanol (Sigma-Aldrich) was used for sample extraction, reconstitution, and creation of calibration curves. For quantitation, five deuterated internal standards were used: methamphetamine-D₅, heroin-D₉, cocaine-D₃, fentanyl-D₅, and THC-D₉ (Cayman Chemical/Cerilliant, 1 mg mL⁻¹ solutions). A 1 mL aliquot of each of the internal standards was added to 1 L of methanol, providing an extraction solvent with an internal standard concentration of approximately 1 µg mL⁻¹. Chromasolv-grade methanol and water (Sigma-Aldrich) were used for the mobile phase with the addition of formic acid (0.1% v/v).