Liquid Chromatography Detectors - The Electrical Conductivity Detector > Page 83

The Electrical Conductivity Detector

The electrical conductivity detector measures the conductivity of the mobile phase. There is usually background conductivity which must be backed-off by suitable electronic adjustments. If the mobile phase contains buffers, the detector gives a base signal that completely overwhelms that from any solute usually making detection impossible. Thus, the electrical conductivity detector a bulk property detector. and senses all ions whether they are from a solute or from the mobile phase.

In order to prevent polarization of the sensing electrodes, AC voltages must be used and so it is the impedance not the resistance of the electrode system that is actually measured. From a physical chemistry stand point the conductivity of a solution is more important than its resistance. However, it is the resistance (impedance) of the electrode system that determines the current across it.

The resistance (R) of any conductor varies directly as its length (L) and inversely as its cross sectional area (a).

Thus,                                                                         

              where (r) specific resistance of the conductor.