“…In general, for all analytes, our assay performed better than or comparable to prior reported assays, even in comparison with assays measuring only a single analyte, which makes it easier to achieve good performance on run time, required sample volume and matrix effects (Aranda et al, 1988;Carlier et al, 2012;Clavijo et al, 2011;Fernandez Mdel et al, 2013;Hisada et al, 2013;Kiriazopoulos et al, 2017;LeGatt et al, 1986;Lillico et al, 2016;Mahlke et al, 2014;Nichol et al, 1980;Nosseir et al, 2014;Palleschi et al, 2003;Parker et al, 2016;Robson & Prescott, 1977;Saari et al, 2012;Suzuki et al, 2017). Furthermore, most assays use a different drug as an internal standard, whereas we used a deuterated form of fentanyl, which shows better comparable behavior to the analytes that are measured than using a different drug.…”