Reversible protein phosphorylation on serine, threonine, and tyrosine residues is essential for fast, specific, and accurate signal transduction in cells. Up to now, the identification and quantification of phosphorylated amino acids, peptides, and proteins continue to be one of the significant challenges in contemporary bioanalytical research. In this paper, a series of surface grafted monoliths in the capillary format targeting phosphorylated serine has been prepared by first synthesizing a monolithic core substrate material based on trimethylolpropane trimethacrylate, onto which a thin surface-imprinted layer was established by oriented photografting of a variety of mono- and bis-imidazolium host monomers at subzero temperature, using six different continuous or pulsed UV light sources. The imprinted monolith capillaries were evaluated in a capillary liquid chromatographic system connected to a mass spectrometer in order to test the specific retention of phosphorylated peptides. Site-specific recognition selectivity and specificity for phosphorylated serine was demonstrated when separating amino acids and peptides, proving that the optimized materials could be used as novel trapping media in affinity-based phosphoproteomic analysis.