As new “bath salt” drugs such as methylone, ethylone, mephedrone, butylone and other methcathinone analogs increase in popularity, toxicologists require native and labeled certified reference materials to accurately identify and quantify the new compounds in patient samples. Internal standards must have quantitation ions that do not interfere with native quantitation ions. There have been problems with use of PFPA and BSTFA derivatives of deuterated internal standards of these methcathinones due to loss of label in the GC/MS fragmentation. An alternate derivatization method is presented in this study.
Native and deuterated reference materials of methylone, ethylone, butylone, mephedrone, and methedrone were synthesized at Cerilliant as HCl salts and were used to develop the derivatization method with trifluoroacetic anhydride (TFAA). The HCl salts were converted to free base with 0.1M sodium bicarbonate and heated at 60 °C for five minutes with TFAA and ethyl acetate to acyalte the amino group. The free up procedure is sensitive to choice of base due to instability of α-amino ketones. Derivatization time is critical, as decomposition occurs with excessive heating.
Derivatives were analyzed directly by GC/MS with cool-on-column injection on a DB-5ms narrow-bore (30m x 0.25mm x 0.25μm) column.
Temperature ramp: 3 min at 150 °C, 150 °C to 200 °C at 10 °C/min, 200 °C to 210 °C at 2 °C/min.
The labeled compounds retain deuterium label from the molecular ion to one or two fragmentations. Quant ion pairs were selected based on ion abundance. Isotopic distribution was evaluated to ensure the majority of the label was on the quant ion.
For Methedrone and Mephedrone, the molecular ion abundance is low. The fragment ion is used for quantiation.
Ethylone and butylone are distinguished by the response of fragment ions 110 and 140 relative to 121 amu.