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Liquid Junction Potentials and Their Effect on Potential Measurements in Biological Systems

1968; Elsevier BV; Linguagem: Inglês

10.1016/s0074-7696(08)61402-3

2163-5854

P. C. Caldwell,

Analytical Chemistry and Sensors

This chapter focuses on the liquid junction potentials and their effect on potential measurements in biological systems. It is virtually impossible to measure the membrane potentials of cells. Absolute values cannot be obtained because it is not possible to measure directly the potential changes which take place between the tip of the recording electrode and its immediate surroundings as it penetrates into a cell from the external medium. This change, which is added to or subtracted from the change due to the membrane potential, arises as a result of electrode processes at the electrode tip and like any other change at a single electrode its absolute value cannot be measured directly. On the other hand, theories of this potential change are available for certain situations and can be used to calculate its effect on the values obtained for resting potentials even though it cannot be measured experimentally. The problem of potential changes at the electrode tip is reduced to a minimum in the salt bridge type of electrode and this type is the most widely used for the measurement of cell membrane potentials, usually in the form of a glass capillary filled with a potassium chloride solution. In the case of capillary electrodes of more than about 5 μ internal diameter the problem is that of the changes in liquid junction potential between the electrode solution and the surroundings and this review is mainly concerned with the ways in which estimates can be made of these potentials and the changes in them. The chapter discusses the equations that have been developed for these potentials, the validity of these equations, and the effects of junction potentials on measurements of nerve and muscle membrane potentials.