<p>This paper reports an on-line sample preconcentration by a sweeping technique based on the surface complexation between TiO₂ (titania) nanoparticles and phosphate groups in the capillary electrophoresis (CE) analysis of phosphopeptides. It is well-known that titania particles can trap phosphopeptides under an acidic condition, while under an alkaline condition they are eluted from the titania surfaces. In the sweeping via solid phase extraction using the titania nanoparticles, a phosphopeptide solution is injected as a long plug into a capillary filled with an acidic background solution. Due to the complexation onto the titania surfaces, the analytes in a long sample zone are swept by the titania particles to a narrow zone. This preconcentration technique was applied to the analysis of monophosphopeptide from β-casein. When an 1% titania dispersion and 100 ppm phosphopeptide solution was successively introduced into the capillary at the injection time of 30 s and 60 s, respectively, a sharp peak of the phosphopeptide was obtained by UV detection without any optical interferences of the titania. Comparing with a conventional CE analysis, a 22-fold sensitivity increase was achieved by the preconcentration effect.</p>