An in-depth study on Z/E-methoxime isomers in gas chromatography-quadrupole mass spectrometry analysis of C6-keto-opioids in human urine as their methoxime- and acyl-derivatives. - Shoffler KM; Barajas DA; Tomedi MR; Hall CL; Reynolds GD; Dinh HT; Castaneto MS; Ke P (Journal of analytical toxicology, 2026)