BACKGROUND-NOISE IN CAPILLARY ELECTROPHORETIC AMPEROMETRIC DETECTION

Six electrolytes were used to evaluate the performance (background noise) of amperometric detection with four electrode materials (C, Pt, Au, Ag). Both filament and disk electrodes (10-25-mu m diameter) were placed either internal or external to the capillary. The large potential fields in the capillary were sufficient to cause oxidation and reduction of the electrolytes, often with bubble formation, along the length of the electrode placed inside the capillary, and electrodes could be dramatically altered when they were exposed to these potential fields. Measurement of the potential fields around the ends of capillaries with different internal diameters showed that the potential field had negligible effects on background noise for capillary internal diameters of less than or equal to 25 mu m. Normal peak-to-peak noise observed with a simple potentiostat design was in the range of 0.05-0.1 pA for end-capillary detection (i.d. less than or equal to 25 mu m). Potential fields were significant (similar to 1 V) at the end of 75-mu m capillaries, and the use of grounded detection zones gave only moderate improvements in peak-to-peak noise.