Distinguishing two isomeric mephedrone substitutes with selective reagent ionisation mass spectrometry (SRI‐MS)

The isomers 4‐methylethcathinone and N‐ethylbuphedrone are substitutes for the recently banned drug mephedrone. We find that with conventional proton transfer reaction mass spectrometry (PTR‐MS), it is not possible to distinguish between these two isomers, because essentially for both substances, only the protonated molecules are observed at a mass‐to‐charge ratio of 192 (C 12 H 18 NO + ). However, when utilising an advanced PTR‐MS instrument that allows us to switch the reagent ions (selective reagent ionisation) from H 3 O + (which is commonly used in PTR‐MS) to NO + , O 2 + and Kr + , characteristic product (fragment) ions are detected: C 4 H 10 N + (72 Da) for 4‐methylethcathinone and C 5 H 12 N + (86 Da) for N‐ethylbuphedrone; thus, selective reagent ionisation MS proves to be a powerful tool for fast detection and identification of these compounds. Copyright © 2013 John Wiley & Sons, Ltd.