Gas Chromatography Detectors - Some Less Common GC Detectors > The Absolute Mass Detector > Page 93

This system was devised by Bevan and Thorburn [43,44], who adsorbed the eluent from a GC column on to the coated walls of a vessel supported on a recording balance. A diagram of their apparatus is shown in figure 61. The adsorption vessel was 1.4 cm I.D. and about 5 cm high. The walls of the vessel were coated with a high boiling absorbent such as polyethylene glycol or an appropriate normal hydrocarbon depending on the samples being trapped. Under such circumstances the solutes separated had to be relatively low boiling otherwise they would condense in the capillary connecting tube to the adsorption vessel. The tube dipped to the base of the absorber where a baffle was situated to direct the eluent to the walls of the adsorption vessel. The balance record represented an integral chromatogram, the step height giving directly the mass of solute eluted.



Despite the relative casual arrangement of the adsorbent, it would appear that the adsorption was quite efficient and, with 10 mg charges on the column, an accuracy of 1% could be easily achieved. Later Bevan et al [45,46], reduced the size of the absorber and employed charcoal as the adsorbing material. Although this improved the performance of the detector and reduced the necessary sample size, the detecting system was never made commercially. Even after modification, its sensitivity was relatively poor and despite it being an absolute detecting system, it placed too many restrictions on the operation of the chromatograph and the samples that could be chromatographed to be generally useful.