We developed a coupled dual column system with an optional post-column derivatization for on-line sample processing, trace enrichment and analysis of aromatic 1,2-diol and aliphatic cis-diol biomolecules (e.g. catecholamines, ribonucleosides). The fully automated high-performance liquid chromatography analyzer tolerates the direct injection of proteinaceous fluids by use of a unique bonded-phase precolumn material which allows the simultaneous performance of covalent affinity and size-exclusion chromatography.