Background noise in capillary electrophoretic amperometric detection

Abstract

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 ( -25-µ 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 <25 µ . 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. < 25 µ ). Potential fields were significant (~1 V) at the end of 75-µ capillaries, and the use of grounded detection zones gave only moderate improvements in peak-to-peak noise.The attractive potential of electrochemical detection in capillary electrophoresis (CE) has been shown for a wide range of analytes, including inorganic ions, small organic molecules, and large biomolecules.1-12 Attractive features of amperometric detection with ultramicroelectrodes include small detection volume, high sensitivity, good selectivity, and low cost. Most initial detector designs1 234 5™6 were based on the principle that to reduce detector noise from the potential field at the end of the capillary, the current in the capillary had to be connected to ground prior to the analyte reaching the working electrode. Indeed, the opinion has been expressed3 that some short-circuiting technique, such as cracking the capillary in front of the working electrode, is a requirement for effective electrochemical detection. These "grounded" detection cells can reduce the amount of the separation current passing through detection zone, but construction of such cells is difficult. It has also been noted4-6 that the background noise in these grounded systems is still affected by the (1) Curry,

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Separation of catecholamines by microchip electrophoresis with a simple integrated laser-induced fluorescence detector

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Detecção eletroquímica em eletroforese capilar

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“…A seguir, esta região é imobilizada, de maneira a aumentar a resistência mecânica do dispositivo. Uma membrana porosa é posicionada ao longo da fratura para que haja condução de corrente, embora alguns autores tenham dispensado o uso da membrana, posicionando o eletrodo utilizado na separação (conectado à fonte de alta tensão) imediatamente após a fratura 26,[34][35][36][37][38][39][40] . Finalmente, o conjunto é colocado em contato com o eletrodo de separação através de eletrólito apropriado.…”