The applicability of trace enrichment and separation of microcontaminants on a 10 mm x 2 mm I.D. high-pressure packed (8 microns C18 bonded silica or 10-15 microns PLRP-S) column combined on-line with an atmospheric pressure chemical ionization MS-MS system is demonstrated for the target analysis of herbicides in river water. Tailor-made procedures are obtained for a limited number of analytes by tuning the chromatographic efficiency of the short LC column and the specificity of tandem MS, in order to minimize the analysis time. With the on-line short-column LC-MS-MS method, good linearity is obtained for the herbicides in the range of 0.1-10 micrograms/l. The relative standard deviations of peak areas are less than 5% and, with only 4-ml samples, detection limits of 0.01-0.1 microgram/l can be achieved. The total analysis time is 10-15 min. The 10 mm x 2 mm I.D. LC columns packed with 8 microns particles show good stability and can be used for at least 40 analyses. Target compound analyses of river water allowed the confirmation of the presence of herbicides such as diuron, simazine, atrazine and terbutylazine at sub-microgram/l levels.