Glass Microelectrodes: the Origin and Elimination of Tip Potentials

Abstract

ONE of the most important artefacts in electrophysiology is the microelectrode tip potential^1,2. Its existence precludes accurate determination of cell membrane resting potentials, particularly with extracellular solutions of low ionic strength where the error may be as large as 50 mV. Adrian¹ found that the tip potential of electrodes filled with 3 M potassium chloride was logarithmically related to the external concentration of sodium chloride or potassium chloride (in an inverse way) and correlated with electrode resistance (correlation coefficient ≈ 0.7). It was concluded that tip potentials are junction potentials produced by some substance blocking the tip of the electrode, reducing the mobility of the chloride ion and exaggerating the difference of mobility of the sodium and potassium ions. This communication is primarily concerned with a simple method for eliminating tip potentials and with an extensive series of observations on the tip potential phenomenon.