Potentiometric sensors in flow systems

The great advantage of these sensors is that they are cheap and disposable the disadvantage is their poor reproducibility. However, there have been many applications, especially in the quantitative detection of drugs of abuse. 

In these sensors the technology developed for ISFET construction is used in conventional electrodes. Links between the membrane and internal reference are metallic (ohmic contact), by deposition of the metal on the membrane (solid state membranes), or by deposition of an ion-selective membrane on a metal. This latter is an integrated sensor. 

An example being researched for possible use is a pH electrode (Fig. 13.13) a metal contact is deposited on an inert substrate followed by a glass film (in an oven) that totally encapsulates the electrical contact19. This would be a considerably more robust pH electrode than those presently used, and easier to maintain. 

Flow methods20 permit the placing of electrochemical sensors at essential control points. Normally a branching of the principal flow is aranged that passes by the sensors any reagents, etc., being added after branching and before the sensor. An on-line response can be extremely important for efficient control. 

Any potentiometric sensor or combination of potentiometric sensors can, in principle, be used in a flow system. Certain precautions have to be 

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