Liquid Chromatography Detectors - The Electrical Conductivity Detector > Page 85


where  (c) is the electrolyte concentration  in gram equivalents /liter.



Thus, the cell resistance is inversely proportional to the electrolyte concentration (c), the equivalent conductance of the electrolyte and the cell geometry [(a) and (L)]. Thus the cell output (which is, in fact proportional to the resistance change of the cell) must be modified to provide an output linearly related to concentration.

The basic sensor, being so simple, has changed little from that first described (1). The sensor volume has been reduced but still consists of two electrodes situated in the column eluent, the resistance (or strictly the impedance) between which is measured by an appropriate electronic circuit. Figure 55 shows three simple forms of the conductivity sensor although many other geometric forms have been described in the literature. The basic sensor is, indeed, very simple, the top design is easily constructed and can have an effective sensing volume of only a few microliters.