Conductance specific, electrophoresis

This type of detection has achieved much development in the last few years due to its simplicity. A specific revision on conductimetric (and potentiometric) detection in conventional and microchip capillary electrophoresis can be found in Ref. [57]. It is considered a universal detection method, because the conductivity of the sample plug is compared with that of the solution and no electroactivity of the analytes is required. Two electrodes are either kept in galvanic contact with the electrolyte (contact conductivity) or are external and coupled capaci-tively to the electrolyte (contactless mode). An alternating current potential is applied across the electrodes and the current due to the conductivity of the bulk solution is measured. As the signal depends on the difference in conductivity between solution and analyte zones, the choice of the electrolyte is crucial. It is necessary that it presents different conductivity without affecting sensitivity. 

Note An important aspect of biocicctrochemial analysis are the processes of electrophoresis and electrical transport (conduction). Questions specific to those topics but appropriate to this chapter arc found in Chapters 23 and 27. 

All electrophoretic processes are essentially charge-transport processes that obey Ohm s law. In electrophoresis, this law is most conveniently expressed in terms of electrical current density, J, specific conductance, k, and electrical field strength, E. 

Along with electrophoresis, the electric field applied to free disperse system causes the flow of electric current, related to both the motion of ions in dispersion medium and charge transfer by particles moving with velocity o . The specific electric conductance of the free disperse system, v, is equal to phenomenological coefficient a22 and includes the specific electric conductance of the dispersion medium,, and the additional conductance caused by moving charged particles. A more detailed consideration shows that for free disperse system... 

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