AN ELECTROCHEMICAL COIL FOR END-COLUMN AMPEROMETRIC DETECTION IN CAPILLARY ELECTROPHORESIS

With end-column amperometric detection in capillary electrophoresis, precise positioning and stabilization of the working electrode are highly important. Noises from vibration and breakage of the microelectrode (e.g,, carbon fiber electrode) are typical problems. To overcome these drawbacks, a new electrochemical cell assembly was designed, In this assembly, alignment of the working electrode with the capillary outlet can be achieved precisely and easily. Coupling with a disk-type Pt electrode (50 mu m diameter), detection limits of 3.0 and 5.2 amol and separation efficiencies of about 70 000 and 150 000 theoretical plates for the determination of dopamine and catechol, respectively, as test compounds can be obtained. The relative standard deviations (n = 21) of migration time and peak current obtained are 3.5, 5.1% and 2.2, 2.7%, respectively, for these two compounds. Applicability of this assembly as an electrochemical detector for capillary electrophoresis was demonstrated by running a synthetic sample containing dopamine, serotonin, norepinephrine, epinephrine, isoproterenol, and catechol. Results obtained are comparable with those from other end-column or off-column determinations.