Liquid chromatography-tandem mass spectrometry of porphyrins and porphyrinogens in biological materials: separation and identification of interfering poly(ethylene) glycol by travelling wave ion mobility spectrometry/tandem mass spectrometry

Biological and clinical samples for porphyrin and porphyrinogen analyses by liquid chromatography-tandem mass spectrometry (LC-MS/MS) are often contaminated with poly(ethylene)glycol (PEG), which complicates the interpretation of mass spectra and characterisation of new porphyrin metabolites. Two contaminating PEG molecules (m/z 833 and m/z 835) were completely separated from uroporphyrin I (m/z 831) by travelling wave ion mobility spectrometry and characterised by tandem mass spectrometry. One of the PEG species (m/z 835) also co-eluted with uroporphyrinogen I (m/z 837) and was unresolvable by travelling wave ion mobility spectrometry/MS, therefore contaminating the MS/MS mass spectra owing to isotope distribution. These PEG species, with the [M + H](+) ions at m/z at 833 and/or m/z 835, co-eluted with uroporphyrin I and uroporphyrinogen I by LC-MS/MS and could be wrongly identified as uroporphomethenes.