Development of a Robust Platform for Infrared Ion Spectroscopy: A New Addition to the Analytical Toolkit for Enhanced Metabolite Structure Elucidation

Metabolite identification is essential in drug metabolism and pharmacokinetics (DMPK) studies and plays a pivotal role throughout the drug development process, from informing drug design to evaluating safety and efficacy. Mass spectrometry (MS) is the analytical technique of choice for characterizing metabolites due to its selectivity and sensitivity, particularly when paired with chromatographic methods. However, MS encounters challenges in structural characterization. This study employs infrared ion spectroscopy (IRIS) to differentiate isomeric compounds and demonstrates the robustness of a newly developed IRIS platform. We showcase applications in metabolite identification by determining the site of glucuronidation and phase I oxidation in selected drug molecules. Employing density functional theory for spectral prediction, IRIS decreases reliance on reference standards and alleviates the time-consuming purification processes typically associated with metabolite analysis. The newly developed platform integrates a high-power, high-repetition-rate infrared laser and ion trap MS. This setup is very robust, as evidenced by the highly reproducible IRIS spectra recorded over a one-year period without any instrument readjustment or recalibration. Moreover, the high power and high repetition rate of the laser provide a large dynamic range that is necessary to resolve all spectral features. These results leverage IRIS toward a transformative tool in analytical chemistry, with potential applications expanding across various fields, such as impurity analysis and forensics. The introduction of a compact IRIS setup in an industrial setting not only confirms its practical applicability but also emphasizes its potential for integration into routine analytical workflows.