Meyer and collaborators identified isofentanyl together with three-methylfentanyl section I and section II metabolites in rat urine (Meyer et al., 2012). Isofentanyl is undoubtedly an isomer of fentanyl and shares some principal fragment ions in MS Assessment. Metabolites including the nor-metabolite can help to unequivocally establish uptake of the compound. http://franciscojexbp.shotblogs.com/the-greatest-guide-to-5f-pcn-drug-14455975