Investigation of the Photoionization Properties of Pharmaceutically Relevant Substances by Resonance-Enhanced Multiphoton Ionization Spectroscopy and Single-Photon Ionization Spectroscopy Using Synchrotron Radiation

Abstract

The photoionization properties of the pharmaceutically relevant substances amantadine, diazepam, dimethyltryptamine, etomidate, ketamine, mescaline, methadone, and propofol were determined. At beamline U125/2-10m-NIM of the BESSY II synchrotron facility (Berlin, Germany) vacuum ultraviolet (VUV) photoionization spectra were recorded in the energy range 7.1 to 11.9 eV (174.6 to 104.2 nm), showing the hitherto unknown ionization energies and fragmentation appearance energies of the compounds under investigation. Furthermore, (1+1)-resonance-enhanced multiphoton ionization (REMPI) spectra of selected compounds (amantadine, diazepam, etomidate, ketamine, and propofol) were recorded by a continuous scan in the energy range between 3.6 and 5.7 eV (345 to 218 nm) using a tunable optical parametric oscillator (spectral resolution: 0.1 nm) laser system. The resulting REMPI wavelength spectra of these compounds are discussed and put into context with already known UV absorption data. Time-of-flight mass spectrometry was used for ion detection in both experiments. Finally, the implications of the obtained physical-chemical results for potential analytical applications are discussed. In this context, fast detection approaches for the considered compounds from breath gas using photoionization mass spectrometry and a rapid pre-concentration step (e.g., needle trap device) are of interest.