Potentiometric sensors concentration standard

Reference electrodes provide a standard for the electrochemical measurements. For potentiometric sensors, an accurate and stable reference electrode that acts as a halfcell in the measurement circuit is critical to providing a stable reference potential and for measuring the change in potential difference across the pH sensitive membrane as the pH concentration changes. This is especially important in clinical applications such as pH measurements in the blood, heart, and brain, where the relevant physiological pH range is restricted to a very small range, usually less than one unit. 

In practice, potentiometric biosensors are used just like any other membrane electrodes or gas-sensing probe. Calibration plots are prepared using known standards of the biomolecule analytes (usually prepared in a given buffer), and exposing the sensors to these solutions until a steady state emf value can be recorded (usually in 1 to 2 minutes). Plots of emf versus log [substrate] are prepared and used to obtain concentration data for unknown samples (either diluted in buffer or nondiluted) that are exposed to the same sensor under exactly the same measurement conditions. 

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