A Certified Reference Material of the major urinary metabolite of methadone. Methadone, sold under various trade names such as Symoron, Amidone or Methadose?, is a synthetic opioid used medically as an analgesic and as a maintenance anti-addictive for use in patients with opioid dependency. Suitable uses for this reference standard include as starting material in preparation of calibrators and controls for LC/MS or GC/MS methods in methadone testing for applications in clinical toxicology or forensic analysis.