Simultaneous concentration enrichment and electrophoretic separation of weak acids on a microchip, using in situ photopolymerized carboxylate-type polyacrylamide gels as the permselective preconcentrator

A method for the simultaneous concentration and separation of weak acids using an acidic polyacrylamide gel, fabricated in the microfluidic channel of a commercial poly(methyl methacrylate)-made microchip, is reported. This approach is based on simple photochemical copolymerization for the fabrication of a permselective preconcentrator. The intersection of the poly(methyl methacrylate)-made microchip was filled with a gel solution comprising acrylamide, N,N'-methylene-bis-acrylamide, and 2-acrylamidoglycolic acid, with riboflavin as a photocatalytic initiator. In situ polymerization, near the cross of the sample outlet channel, was performed by irradiation with an argon ion laser beam that is also used as the light source for fluorimetric detection. The electrokinetic properties, combined with electrostatic repulsion between sample components and the anionic groups on the polyacrylamide gel, enable the entrapment and concentration of weak acids at the interface of the cathodic side of the gel plug. This method displays concentration factors of up to 10(5) within 3 min. The effectiveness of the ionic preconcentrator was demonstrated by the sensitive analysis of fluorescein isothiocyanate-labeled amino acids.