A B Flow rates were varied from 8 to 100 µL/min and CV was scanned at SV 600 V. CV values shift as flow rates are modified, 100 µL/min was found to be the optimal for resolving the isomeric pairs BZE/NCOC and ODT/NDT (Figure ). As shown above, acetonitrile provides better resolution of the isomeric pairs, so the effect of varying the content of acetonitrile was investigated for resolution (Figure ). CV values slightly change as a function of the % acetonitrile, except for BZE for which the CV values becomes more positive as the % acetonitrile increased, eventually reaching the same CV value as NCOC (10 V), its isomeric partner. Overall, 20 % acetonitrile and 100 µL/min were found to be optimal for resolving the isomeric pairs. Subsequently, CV was scanned using the optimized DMS conditions; cell temperature 60°C, pressure 33 mbar, F value 2, SV 600 V, flow rate 100 μL/min and 20/80 ACN/H2O + 0.1% FA as mobile phase. Figure presents the ionograms with CV values for optimized separation of cocaine, tramadol, and their metabolites. Under these optimized conditions the isomeric pairs are baseline separated, the resolution between the isomers BZE/NCOC is RS=27.34 and PC= 13.63. For the isomers ODT/NDT resolution was RS=8.51 and PC=4.24. Under conditions considered the THC/CDB could not be separated in positive mode contrary to Masmoushi et al. which reported the separation of THC/CBD in negative mode with 1.5% IPA modifier on an atmospheric pressure DMS device .