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In this study, we assessed three liquid chromatographic platforms: reversed phase (RP), aqueous normal phase (ANP), and hydrophilic interaction (HILIC) for the analysis of polar metabolite standard mixtures and for their coverage of urinary metabolites. The two zwitterionic HILIC columns showed high-quality chromatographic performance for metabolite standards, improved separation for isomers, and the greatest coverage of polar metabolites in urine. In contrast, on the reversed phase column, most metabolites eluted very rapidly with little or no separation. Using an Exactive Orbitrap mass spectrometer with a HILIC liquid chromatographic platform, approximately 970 metabolite signals with repeatable peak areas (relative standard deviation (RSD) ≤ 25%) could be putatively identified in human urine, by elemental composition assignment within a 3 ppm mass error. The ability of the methodology for the verification of nonmolecular ions, which arise from adduct formation, and the possibility of distinguishing isomers could also be demonstrated. Careful examination of the raw data and the use of masses for predicted metabolites produced an extension of the metabolite list for human urine.
Zhang et al. (Wed,) studied this question.