Noise in Glass Microelectrodes

A recent study by DeFelice and Firth (1971) has shown that the electrical noise present in glass microelectrodes is in excess of the Johnson noise predicted by the Nyquist formula given in Section 4.4.3. If the microelectrode lumen is filled with an electrolyte of concentration ri2 and the external electrolyte in which the electrode is immersed has the concentration when = ri2 2i noise voltage is observed as predicted by the Nyquist formula. When Ml offset voltage is noted (tip potential) because of the 

DeFelice and Firth found that the mean square voltage fluctuations per cycle (n 2) can be represented by 

At present, the origin of excess noise when nj 9 nj is not understood. 

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