A reactive monolith based on the polymerization of 3-chloro-2-hydroxypropyl methacrylate, (HPMA-Cl), with a crosslinking agent, ethylene glycol dimethacrylate (EDMA), was synthesized and post-functionalized with a macromolecular ligand polyethyleneimine. Monolithic columns with controlled permeability and pore structure were prepared by free radical polymerization in the presence of a binary porogenic mixture of isopropanol and decanol. The presence of chloropropyl functionality in the pristine monolith allowed the synthesis of a post-fuctionalized monolith carrying cationic groups that was used to control the magnitude of electroosmotic flow (EOF) in electrochromatographic separation. In the synthesis of pristine monoliths, the feed concentration of functional monomer (ie, HPMA-Cl) was changed between 30 and 60v/v % for obtaining cationic monoliths providing satisfactory electrochromatographic separation. The best electrochromatographic performance was obtained with the polyethyleneimine functionalized monolith prepared by using the pristine monolith obtained by 60% (v/v) monomer concentration. This monolith was used in reversed phase and hydrophilic interaction capillary electrochromatography modes for the separation of alkylbenzenes, polycyclic aromatic hydrocarbons, phenols, and nucleosides, using mobile phases with low acetonitrile (ACN) contents ranging between 20% and 35% (v/v). This ACN range was remarkably lower than the content of ACN used on the hydrophilic polymethacrylate-based monoliths reported previously (ie, >90%). The plate heights up to 5.3m were obtained for the separation of nucleosides with the environmental friendly mobile phases whose ACN contents were also remarkably lower than that of similar polymethacrylate-based monoliths.