Old and new synthetic and semi-synthetic opioids analysis in hair: A review

New Psychoactive Substances (NPS), and particularly synthetic opioids, are constantly growing in the illicit market, and represent a particular danger due to their high potency and the fact that they're often not covered by legislation yet. Thus, there is the constant need for sensitive, reliable and reproducible techniques to detect and identify these substances in a variety of different matrices, both for clinical and forensic purposes. In particular, hair analysis can provide important information on past and/or continuative use of different substances such as psychoactive drugs.In this study, we report a review of the existing literature on synthetic opioids analysis in hair, in order to summarize the analytical methods currently used for synthetic and semi-synthetic opioids and NPS hair testing. Methanol with addition of diluted acidic solution represents the most frequently extraction solution. Purification procedures, either carried out through solid phase or liquid/liquid are still needed in order to achieve an adequate sensitivity; in particular, several methods provided a limit of detection lower than 1 pg/mg for most of the monitored substances. Chromatographic techniques coupled with mass spectrometric systems confirmed to be the best choice among the available analytical techniques for monitoring psychoactive substances and metabolites in keratin matrices. Though high-resolution mass spectrometric instruments, such as Time of Flight, are gaining interest, triple quad still guarantees better sensitivity. Beside common synthetic and semi-synthetic opioids, such as hydromorphone, hydrocodone and tramadol, the most frequently detected compounds in hair samples, among fentanyl derivatives, are furanyl fentanyl, sufentanil and butyryl fentanyl.