Gas Chromatography Detectors - Some Less Common GC Detectors > The Discharge Detector > Page 84
The Discharge Detector
About the same time that Ryce and Bryce were developing the thermionic ionization detector, Harley and Pretorious (33) and (independently) Pitkethly and his co-workers (34,35) were developing the discharge detector. By applying the appropriate potential, a discharge can be maintained between two electrodes situated in a gas providing the pressure is maintained between 0.1–10 mm of mercury. After the discharge has been initiated, the electrode potential can be reduced and the discharge will still continue. Under stable discharge, the electrode potential remains constant and independent of the gas pressure and the electrode current.The electrode potential, however, depends strongly on the composition of the gas. It follows, that the system could function as a GC detector. Pitkethly modified a small domestic neon lamp for this purpose and a diagram of his sensor is shown in figure 48.The lamp was operated at about 3 mm of mercury pressure with a current of 1.5. Under these conditions the potential across the electrodes was 220 V. Pitkethly reported that a concentration of 10-6 g/l gave an electrode voltage change of 0.3 V.
Figure 48. The Discharge Detector