Gas Chromatography Detectors - Early Gas Chromatography Detectors > The Gas Density Balance > Page 22

Early Gas Chromatography Detectors

The first GC detector was invented by James and Martin [4] in 1952, and used for the separation of some fatty acids. It consisted of a titration apparatus situated at the end of the column and the eluent gas was bubbled through a suitable aqueous liquid to absorb the solutes. The solution contained an indicator and, as each solute was eluted, the solution was manually titrated. The titration process was eventually automated and an integral chromatogram was obtained by plotting the volume of base solution added against time. The integram consisted of a series of steps, one for each solute. This rather primitive arrangement validated the gas chromatographic concept but also indicated that a detector with greater sensitivity and a more catholic response was necessary for the effective use of the technique.

The next detector, the first really practical detector to be developed, was also invented by James and Martin but, for some reason it seems, was never formally reported in the literature. Its description, however, did appear in a review by A. T. James [5] and a detailed explanation of the function described by Munday and Primavesi [6].

The Gas Density Balance

The gas density balance was a very complicated and ingenious device and, incidentally, the modern 'so–called' gas density bridge bears little or no resemblance to the original design. A diagram of the gas density balance is shown in figure 7. The detector consisted of a compact Wheatstone network of capillary tubes, drilled out of a high conductivity copper block. The reference flow of mobile phase and the eluent from the column entered at two opposing junctions of the bridge arms (the center of tube (C)) such that the eluent was contained in one vertical arm (C) and the pure mobile phase in a parallel vertical arms (A) and (B).



Figure 7 The Martin Gas Density Bridge