“…Data is acquired in an untargeted manner and can be retrospectively analyzed for new and emerging synthetics. In recent years, LC-HRMS has been used for the detection of synthetic opioids such as butyrfentanyl, 4-fluorobutyrfentanyl, acetylfentanyl, 4-methoxybutyrfentanyl, furanylfentanyl, acrylfentanyl, 4Cl-iBF, 4F-iBF, THF-F, cyclopentylfentanyl, AH-7921, MT-45, and U-47700 in individual cases, case series, outbreaks, and epidemiological surveillance efforts (Backberg et al, 2015;Wohlfarth et al, 2016;Helander et al, 2016;Schneir et al, 2017;Armenian et al, 2017;Breindahl et al, 2017;Jones et al, 2017;Steuer et al, 2016;Vo et al, 2017;Fleming et al, 2017;Guerrieri et al, 2017;Helander et al, 2017;Goggin et al, 2017;Watanabe et al, 2017;Fels et al, 2017). It has also been used for the elucidation of the metabolic pathways of emerging synthetic opioids, such as, AH-7921, butyrfentanyl, carfentanil, U-47700, furanylfentanyl, acetylfentanyl, acrylfentanyl, and 4F-iBF Jones et al, 2017;Steuer et al, 2016;Feasel et al, 2016;Fleming et al, 2017;Goggin et al, 2017;Watanabe et al, 2017).…”