A PERFLUOROSULFONATED IONOMER JOINT FOR CAPILLARY ELECTROPHORESIS WITH ON-COLUMN ELECTROCHEMICAL DETECTION

A new fabrication method for a Nafion joint for capillary electrophoresis with on-column electrochemical detection (CEEC) is described. The Nafion joint was cast directly on the capillary column. A tungsten wire was used to define the now channel during fabrication and removed for operation. This method allowed the construction of Nafion joints over 1 mm in length, which did not significantly contribute to band broadening. The increased length of these joints resulted in a significant decrease in the noise at the electrochemical detector. The relationship between the noise, the magnitude of the electrophoresis current, and the length of the Nafion joint was investigated. The separation efficiency of a CEEC system equipped with this type of Nation joint was investigated using hydroquinone, phenolic acids, and catecholamines. Using 10 mM phosphate buffer at pH 6.1 for the ran buffer, the Nafion joint did not have a significant effect on the separation efficiency of neutral or acidic compounds; however, the cationic compounds exhibited significant band broadening. The interaction of cations with the Nation was minimized by use of a 100 mM EPPS zwitterion, pH 6.0, running buffer. A detection limit of 5 x 10(-10) M was achieved for hydroquinone and 2 x 10(-9) M for the phenolic acids using the phosphate running buffer. A slightly higher detection limit of 5 x 10(-9) M was achieved for the catecholamines using the EPPS running buffer.