“…A number of high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) methods that quantified morphine, M3G and M6G and those that quantified clonidine in human plasma were reviewed. The lowest limits of quantification (LLOQ) were 0.25-3.5 ng/mL for morphine, 1-3.5 ng/mL for M3G/M6G (Clavijo et al, 2011;Eckart et al, 2015;Ghassabian et al, 2012) and 0.01-0.25 ng/mL for clonidine (Danafar & Hamidi, 2016;Muller et al, 2007;Nirogi, Kandikere, Mudigonda, & Komarneni, 2008;Parekh, Pudage, Joshi, Vaidya, & Gomes, 2008;Qin et al, 2015;Zhuang et al, 2015), and these methods required plasma volumes ranging from 100 μL up to 1 mL. There was one published HPLC-MS/MS method that simultaneously quantified clonidine, morphine and its two major metabolites that was highly sensitive and only required 100 μL of plasma (Veigure et al, 2017).…”