Xevo tqd tandem mass spectrometer

All reagents except ammonium hydroxide were of LC/MS grade. Acetonitrile, methanol, formic acid, 29% ammonium hydroxide and acetic acid were supplied by Fisher Scientific (Hampton, NH). Buprenorphine reference standard was purchased from Sigma‐Aldrich (Sigma‐Aldrich RTC, Laramie, WY, USA). Ultrapure water was supplied by Water Corporation (Milford, MA, USA). Phosphoric acid was supplied by Aldrich Chemistry. Analysis of buprenorphine was carried out via ultra‐performance liquid chromatography (UPLC) and tandem mass spectrometric (MS/MS) detection (Waters Corporation). The UPLC‐MS/MS system consisted of a Waters Acquity UPLC I class Binary Solvent Manager, Acquity UPLC Sample Manager FTN and a Xevo TQD tandem mass spectrometer (Waters Corporation).

Amino acids were measured after extraction with methanol without derivatization (Neobase Kit; Perkin Elmer, Turku, Finland) on an XEVO‐TQD tandem mass spectrometer (Waters, Milford, MA). Briefly, 4 μL of plasma or urine were spotted onto prepunched plain filter paper (Ahlstom 226) in 96‐well plain uncoated microtiter plates. Amino acids were extracted with 100 μL of methanolic extraction solution containing stable isotope‐labeled internal standards by shaking for 45 minutes at 45°C. Twenty microliters of extract were then injected with a flow rate of 10 μL/min directly into the tandem mass spectrometer and measured afterward in multiple reaction monitoring mode. In addition to the amino acids, which are incorporated in the Neobase Kit, ADMA was added to the multiple reaction monitoring experiment with the following settings: parent ion, 203.1 Da; daughter ion, 46.1 Da; dwell time, 0.05 seconds; cone voltage, 26 V; and collision energy, 37 eV.