Poly (acrylic acid) microchannel modification for the enhanced resolution of catecholamines microchip electrophoresis with electrochemical detection

A new modification of glass electrophoresis microchips based on poly (acrylic) acid immobilization has been performed. It is based on the reaction of PAA with an amine functionalized surface, obtained through the bifunctional reagent 3-aminopropyl triethoxysilane. Parameters affecting all the three steps involved: surface activation, silanization and polymer immobilization were optimized employing soda-lime glass plates. Characterization by SEM and XPS was carried out. Application of the modified microchips to the separation of a model system: dopamine (D), epinephrine (E) and norepinephrine (NE), that on the other hand are of high clinical relevance was performed employing amperometric detection. Modification is necessary for obtaining partial resolution of all the three analytes in a microchip with an effective separation length of 30 mm. Situation changes from no resolution (Rs) at all (only one peak was achieved for the mixture) to a partial resolution (Rs D–NE and Rs NE–E are 0.25 and 0.24 respectively). Microchips with 60 mm of separation channel were also modified, implying this procedure a resolution enhancement (Rs of 0.49 and 0.28 for D–NE and NE–E respectively), even when methanol is employed as organic modifier (Rs values of 0.70 (D–NE) and 0.66 (NE–E) for a 3% MeOH).