On-line preconcentration in capillary electrophoresis using monolithic methacrylate polymers

Monolithic methacrylate polymers have been prepared at the inlet end of a capillary by photoinitiated polymerization and used for preconcentration in capillary electrophoresis. The function of the polymer as a preconcentration phase was demonstrated using solutions of S-propranolol. The sample was initially loaded onto the capillary using a high-pressure rinse. After removing unbound sample, the capillary was filled with separation/elution buffer from the outlet end using the electroosmotic flow as a pump (reverse polarity). The sample was desorbed as the separation/elution buffer passed through the polymer and was concentrated into a narrow band. The sample loading and desorption procedure was built into the analysis method thereby making this an on-line preconcentration procedure. A detection limit in the low nanomolar range was achieved for S-propranolol using this polymer for on-line preconcentration in capillary electrophoresis without compromising separation efficiency. The sensitivity enhancement can be improved further by rinsing the sample through the capillary for longer times, up to the saturation point of the polymer.