Isomer-Specific Two-Color Double-Resonance IR2MS3 Ion Spectroscopy Using a Single Laser: Application in the Identification of Novel Psychoactive Substances

The capability of an ion trap mass spectrometer to store ions for an arbitrary amount of time allows the use of a single infrared (IR) laser to perform two-color double resonance IR-IR spectroscopic experiments on mass-to-charge (m/z) selected ions. In this single-laser (IRMS3)-M-2 scheme, one IR laser frequency is used to remove a selected set of isomers from the total trapped ion population and the second IR laser frequency, from the same laser, is used to record the IR spectrum of the remaining precursor ions. This yields isomer-specific vibrational spectra of the m/z-selected ions, which can reveal the structure and identity of the initially co-isolated isomeric species. The use of a single laser greatly reduces the experimental complexity of two-color (IRMS3)-M-2 and enhances its application in fields employing analytical MS. In this work, we demonstrate the methodology by acquiring single-laser (IRMS3)-M-2 spectra in a forensic context, identifying two previously unidentified isomeric novel psychoactive substances (NPS) from a sample that was confiscated by the Amsterdam Police.

Automated summary

The ion trap mass spectrometer allows for two-color double resonance IR-IR experiments on mass-to-charge selected ions using a single infrared laser. This simplifies the experimental complexity and enhances the application in analytical MS field. In a forensic context, the methodology was demonstrated by identifying previously unidentified isomeric novel psychoactive substances from a confiscated sample by the Amsterdam Police.