Gas Chromatography - Tandem Techniques - Introduction > Historical Development of GC Spectroscopy Systems > Page 3

 

It is fairly obvious that the mass spectrometer (MS) would be the first choice for an associated spectroscopic identifying system. In fact, only four years after the first disclosure of GC as an effective separation technique by James and Martin in 1953, Holmes and Morrell (1957) (2), successfully combined the gas chromatograph with the mass spectrometer to produce the first combined system. The authors connected the GC column outlet directly to the mass spectrometer employing a split flow system. The results, in modern terms, were not very impressive, but, without doubt, they demonstrated the practicability of the GC/MS system. The MS not only had the necessary sensitivity but could also partly handle the relatively high accompanying flow of gas which was pumped away by the vacuum system of the mass spectrometer. However, at that time, the capillary column had not been invented (although the concept had been suggested by Martin in his introductory lecture at the 1956 Symposium on Vapor Phase Chromatography) and, thus, the relatively large gas flow rates were difficult to accommodate by direct GC-MS coupling. The problem associated with high gas flow rates and low solute concentration provoked the development of a number of vapor concentrator interfaces that selectively removed the carrier gas and, at the same time, increased the concentration of solute. These devices helped render the GC/MS system viable and useful before the advent of capillary columns. At this time, the chromatographer saw the mass spectrometer as some form of elaborate detector while the mass spectroscopist saw the chromatograph as merely a complex sampling device.

 

Having established the viability of the GC/MS combination, an appropriate mass spectrometer had to be designed that could be easily interfaced with a gas chromatograph. It would need to have 'fast scanning' facilities so that mass spectra could be taken across the peak as it was eluted and have sufficient sensitivity to provide spectra from even peaks from trace materials. This was necessary to ensure the peak was homogeneous and not a concentration envelope containing two or more peaks. The design of the first mass spectrometer to be specifically constructed for a GC/MS system evolved largely from the work of Bill Kelley at the Unilever Research Laboratories at Sharnbrook and Ted Adlard at the Shell Research Laboratories at Thornton in the UK. Initially the work was carried out on a small mass spectrometer the MS2, but the ultimate result of their work was the design of the MS 12 which was a (what was then considered) 'fast scanning' mass spectrometer. The basic design of the MS 12 is shown in figure 2 (Banner et al. Ref 5).