It is generally recognized that sample treatment often is the bottleneck in trace-level organic analysis. As far as column liquid chromatography (LC) is concerned, the design, and commercialization, of on-line and fully automated precolumn/analytical column LC systems with diode-array UV or mass spectrometric detection is a distinct step towards solving the existing problems. Small precolumns that can be packed with sorbents of divergent selectivity, and also on-line (electro)dialysis modules, have been shown to perform well in many environmental and biomedical applications. In addition, it is noteworthy that LC or rather, LC-type, trace enrichment and clean-up on such precolumns are increasingly being used as an on-line treatment step for aqueous samples prior to capillary gas chromatographic analysis.