In this detailed analytical study, we have evaluated in-house synthesised polymeric solid-phase extraction (SPE) sorbents in the form of monodisperse, hypercrosslinked polymer microspheres with diameters in the low micrometre range (approximately 4 microm). More specifically, their performance in the on-line SPE of a group of polar pollutants has been investigated thoroughly. The novel hypercrosslinked materials were compared with satisfactory results to commercial SPE sorbents with similar chemical and morphological properties, albeit that the commercial materials had higher particle sizes and broader particle size distributions. The on-line SPE method developed using these novel particles as packing material was applied successfully to ultrapure, mineral, tap and Ebre river water samples, with near total recoveries of all the analytes studied when 500 ml samples were percolated through the sorbents. Method validation with river water samples demonstrated good linearity, low detection limits as well as satisfactory precision in terms of repeatability and reproducibility, with values of relative standard deviation (%RSD) lower than 6.7 and 8.7%, respectively.