“…Several analytical methods have been developed for quantitation of BUP in biological samples. Early analytical methods included quantitation of BUP by high‐performance liquid chromatography (HPLC) coupled to ultra‐violet (UV) (Hackett et al ., ), fluorescence detection (Ho et al ., ) or GC (Blom et al ., ). Several liquid chromatography coupled to mass spectrometry (LC–MS) methods have also been developed for analysis of BUP in whole blood (Hoja et al ., ), plasma (Ceccato et al ., ; Liu et al ., ; Moody et al ., ; Murphy and Huestis, ; Polettini and Huestis, ; Regina and Kharasch, ), serum (Scislowski et al ., ), urine (Fox et al ., ; Hegstad et al ., ; Kacinko et al ., ; Kronstrand et al ., ; Liu et al ., ; McMillin et al ., ; Regina and Kharasch ) and umbilical cord (Concheiro et al ., ).…”