Improved metabolite characterization by liquid chromatography – Tandem mass spectrometry through electron impact type fragments from adduct ions

Highlights: • Collision induced and electron induced dissociation were studied for the LC-MS analysis of low molecular weight compounds. • For Na and K adducts a radical cation M^{• +} and EI type fragments were observed in the electron induced dissociation spectra. • Electron induced dissociation of [M+H]⁺ precursors, generated radical dications [M+H]^{• 2+} species. Using a chimeric collision cell mounted on a quadrupole time-of-flight platform, collision induced dissociation (CID) and electron induced dissociation (EID) were investigated for the LC-MS analysis of low molecular weight compounds including drugs and endogenous metabolites. Compared to CID, EID fragmentation of the [M+H]⁺ species (10–20 eV) from standard compounds resulted in additional specific and informative fragments, mostly due to neutral losses and, in some cases due to ring openings. Some analytes, for example reserpine and vinpocetine, provided characteristic [M+H]^{• 2+} species. For most analytes for sodium and potassium adducts and multimers a radical cation M^{• +} and electron impact type fragments were observed in the EID spectra, providing the opportunity to use EI libraries to support metabolite identification. EID opens the possibility to get structural information from adduct ions which is often not the case with CID. EID enabled the putative characterization of two metabolites in rat urine as glucuronides of 5,6-dihydroxyindole based on EID fragmentation of the potassium adducts.