M6g d3

Methanolic solutions of morphine, M3G, morphine-6-glucuronide (M6G), normorphine, hydromorphone and 6monoacetylmorphine (MAM) (1 mg/mL) and the deuterated internal standards (IS) morphine-d3, M3G-d3, M6G-d3 and MAM-d3 (0.1 mg/mL) were obtained from Cerilliant (delivered by Sigma-Aldrich, Buchs, Switzerland). Water was purified with a Purelab Ultra millipore filtration unit (Labtech, Villmergen, Switzerland) and acetonitrile of HPLC grade was obtained from Fluka (Buchs, Switzerland). All other chemicals used were from Merck (Zug, Switzerland) and of the highest grade available.

Standard substances and their respective stable isotope labeled internal standards (IS): M3G, M6G, morphine, clonidine, MiOH, midazolam, M3G-D3, M6G-D3, morphine-D6 and MiOH-D4 were obtained from Cerilliant (Texas, USA). Clonidine-D4 and midazolam-D6 were obtained from the Toronto Research Chemicals Inc. (Toronto, Canada). Other reagents used: LC-MS Ultra chromasolv grade methanol (MeOH) from Sigma Aldrich (Missouri, USA), LC-MS grade formic acid from Sigma Aldrich (Missouri, USA), LC-MS grade ammonium hydroxide solution from Sigma Aldrich (Missouri, USA), LC-MS grade 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) from Sigma Aldrich (Missouri, USA). Water was purified (18.2 MΩ•cm at 25 °C and and a total organic carbon (TOC) value 2 -3 ppb) in-house using a Millipore Advantage A10 system from Millipore (Bedford, USA). Plasma and whole blood were purchased from Blood Bank of Tartu University Hospital.