A new procedure for capillary liquid chromatography-electrospray (CLC-ES) mass spectrometry is described. Using this procedure, coupling of a CLC column to a low-flow-rate ES interface is made simple. A 5-cm precolumn and a 35-cm analytical column, both fused-silica capillaries with an i.d. of 100 microm and packed with 3-microm octadecylsilane-bonded material, are coupled in series to a sheathless ES emitter. One solvent splitter is positioned between the loop injector and the precolumn, and a second, between the precolumn and the analytical column. By opening and closing the splitters in the appropriate order, this arrangement permits the injection of 1-20 microL of sample solution with analyte focusing onto the top of the precolumn, followed by isocratic or gradient elution at a flow rate of 0.2-0.3 microL/min through the analytical column. The relative standard deviation of the retention times of reference compounds was <3.5% (n = 5). The potential of the system in metabolome analysis, in which numerous isomeric compounds will require identification, is illustrated by the application of the system to the analysis of steroid sulfates in plasma.