Gas Chromatography Detectors - Ionization Detectors > The Thermal Argon Detector > Page 61

In due course the tritium was replaced by Ni63 (another, more energetic b–ray source) but a fairly safe source that can be operated at relatively high temperatures without fear of contamination. Employing radium as the active source, themicroargon detector was used by Scott (23), with long Nylon capillary columns for the separation of hydrocarbon mixtures. The column was 1000 ft long giving 0.75 x 106 theoretical plates. A chromatogram of the separation is shown in figure 30. It is seen that the sensor volume has no effect on the column performance and the detector is now very suitable for use with capillary columns. The modifications carried out to reduce the effective sensor volume did not improve its linearity nor increase its linear range. However, the noise level was reduced by about two orders of magnitude and thus the sensitivity was commensurably increased by the same amount making it 10 times more sensitive than the FID.

The Thermal Argon Detector

Beres et al. (24) showed that the argon detector could be made to function without a radioactive source or other electron producing device providing the argon and sensor system was operated at temperatures above 150oC. Glass becomes conducting at temperatures of 150oC and above, and so glass could be employed as one of the electrodes. A diagram of a sensor is shown in figure 31.

Figure 31 The Thermal Argon Detector Sensor