Enrichment tags for enhanced-resolution profiling of the polar metabolome

The advanced version of metabolite enrichment by tagging and proteolytic release (METPR) is described that has improved the resolution and structural characterization of polar metabolites from complex biological systems. The enhanced resolution afforded by hydrophobic METPR tags have minimized overlap in tandem MS profiles for polar metabolites and the inclusion of a chlorine atom in the hydrophobic tags have permitted MS-based discrimination of tagged metabolites.