Quantification of Kratom Alkaloids in Plasma

Dextromethorphan, Dextromethorphan-d₃, dextrorphan, 1′-hydroxymidazolam, 4-hydroxymidazolam, 7-hydroxymitragynine, midazolam, midazolam-d₄, mitragynine, and mitragynine-d₃ were purchased from Cayman Chemical (Ann Arbor, MI). The kratom indole alkaloids speciociliatine, speciogynine, mitraciliatine, paynantheine, and isopaynantheine were isolated and purified from commercial kratom products as described^{3 (link),5 (link)}; all reference standards were verified to be ≥95% pure as measured by ultra-high-performance liquid chromatography-ultraviolet spectroscopy (UHPLC-UV) analysis. tert-Butyl methyl ether was purchased from Sigma-Aldrich (St. Louis, MO). Acetonitrile and methanol were purchased from Fisher Scientific (Fair Lawn, NJ). Blank human plasma (K₂EDTA, pooled, mixed gender, lot HMN99236) was purchased from BioIVT (Westbury, NY). All other chemicals and reagents were analytical grade.