Electrical Conductivity Detection

This method consists essentially of measuring the voltage drop across two electrodes immersed in the buffer contained in the capillary tube. Thus, a signal will be produced as soon as a substance of different mobility to that of the buffer passes between the electrodes. It is clear that this will only be effective if the mobility’s of the substances of interest differ significantly from that of the buffer. The potential gradient detector is similar in principle.

The surface area of each electrode must be minimal to avoid electrochemical reactions taking place (e.g. the formation of bubbles). Platinum or platinum iridium wire 0.05 mm in diameter is commonly used and sealed through laser-drilled holes in the quartz tube. Sometimes leakage currents can cause a ‘noise’ problem that can sometimes be avoided by including a non-ionic detergent in the buffer such as hydroxypropylcellulose. Another form of conductivity detector is the ampiometric detector which although electrical in nature functions on a somewhat different principle.