Isotopologue ratio analysis in organic compounds using ESI-FTMS: origin of caffeine in foods

Novel approaches using electrospray ionization (ESI) and Fourier transform mass spectrometry (FTMS) enable for the first time routine, simultaneous analysis of multiple isotope ratios on intact complex molecules. In this study Thermo Scientific™ Orbitrap™ MS was used for high precision and accuracy analysis of several caffeine isotopologue ratios. Alignment of this novel ESI-Orbitrap IRMS approach with the results of classical techniques for isotope ratio analysis will be shown for well characterized caffeine reference materials.

The presence of matrix contaminants can decrease the precision and accuracy of ESI-Orbitrap isotope ratio analysis. Therefore, isotope ratio analysis of caffeine in complex sample matrices requires prior purification. Different ways for the online coupling of reversed phase liquid chromatography were developed and evaluated with respect to high precision isotope ratio analysis of caffeine from complex sample matrices. These developments will be demonstrated for analysis of caffeine reference materials and caffeine in different drinks to obtain information about its natural or synthetic origin.

The online coupling of liquid chromatography with ESI-FTMS expands the application areas for compound specific isotope ratio analysis on polar compounds. This can enable the tracing of metabolites in complex systems with multiple reaction pathways without the need for heavy isotope labelling.