Calibration curve and linear response slope of pH microelectrodes

2 Calibration curve and linear response slope of pH microelectrodes 

The principle of pH electrode sensing mechanisms which are based on glass or polymer membranes is well investigated and understood. Common to all potentiometric ion selective sensors, a pH sensitive membrane is the key component for a sensing mechanism. When the pH sensitive membrane separates the internal standard solution with a constant pH from the test solution, the potential difference E across the membrane is determined by the Nemst equation  

It is clear from the Nemst equation that the temperature of the solution affects the response slope (2303RT/F) of the calibration curve. The electrode voltage changes linearly in relationship to changes in temperature at a given pH therefore, the pH of any solution is a function of its temperature. For example, the electrode response slope increases from 59.2mV/pH at 25°C to 61.5mV/pH at a body temperature of 37°C. For modem pH sensing systems, a temperature probe is normally combined with the pH electrode. The pH meter with an automatic temperature compensation (ATC) function automatically corrects the pH value based on the temperature of the solution detected with the temperature probe. 

Response time is defined as the time at which the pH concentration in a solution is changed on contact with a pH sensor and a reference electrode has reached 95% (or 90%) 

Electrochemical Sensors, Biosensors and Their Biomedical Applications 

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