. After its introduction by James and Martin, the technique of GC developed at a phenomenal rate, growing from a simple research novelty to a highly sophisticated instrument, having a multi-million dollar market, in only 4 years. The gas chromatograph was also one of the first analytical instruments to be associated with a computer which controlled the analysis, processed the data and reported the results. A more sophisticated form of the gas chromatograph was constructed by James and Martin and described by James in 1955 (3). The instrument was a somewhat bulky device with a straight packed column, 3 ft long, that was held vertically and thermostatted in a vapor jacket. Initially, the detector was situated at the base of the column and consisted of the automatic titrating device, the separation was presented as a chromatogram in the form of a series of steps, the height of each step being proportional to the mass of solute eluted. The apparatus was

to separate the fatty acids, those that were radioactive needed to be identified and the relative activity of each peak compared and to do this successfully, a proportional radioactive detector was required. James and Piper described a radioactivity detector 1961-3 [27,28] suitable for this purpose is still in use today, although the detector has been fabricated in various different forms by a number of different manufacturers. A diagram of the radioactivity detector based on the device of James and Piper is shown in figure 46. There are two basic forms of the radioactivity detector, one that measures 13C only and the other that measures both 13C and 3H. In both systems the carrier gas used must be helium or argon and the column eluent is fed through a furnace packed with copper oxide to oxidize all the solutes to carbon dioxide and water. Figure 46 The Radioactivity Detector

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

References 1. A. J. P. Martin and R. L. M. Synge, Biochem. J., 35 (1941)1358. 2. A. T. James and A. J. P. Martin, Biochem. J., 50 (1952) 679. 3. A. T. James, The Times Science Review, Summer (1966)8. 4. D. H. Desty, A. Goldup and B. F. Wyman, J. Inst. Petrol., 45(1959)287. 5. R. D. Dandenau and E. M. Zenner, J. High Res. Chromatogr., 2(1979)351. 6. K. L. Ogan, C. Reese and R. P. W. Scott, J. Chromatogr. Sci., 20(1982)425. 7. J. Harley, W. Nel and V. Pretorious, Nature, London, 181(1958)177

References  1. I. A. Fowlis and R. P. W. Scott, J. Chromatogr., 11(1963)1.  2. J. E. Lovelock, "Gas Chromatography 1960" (Ed. R. P. W. Scott),      Butterworths, London, (1960)26.  3. C. G. Scott, ASTM E19 No. E689–79.  4  A. T. James and A. J. P. Martin, Biochem. J. 50(1952)679.  5. A. T. James, The Times Science Review, Summer (1955)8.  6. C. W. Munday and G. R. Primavesi, "Vapor Phase      Chromatography", (Ed. D.H. Desty and C. L. A. Harbourn),       ButterworthsScientific  Publications,(1957)146.  7. N. H. Ray, J. Appl. Chem., 4(1954)21.  8.  R. P. W. Scott, "Vapor Phase Chromatography" (Ed. D.H. Desty       and C. L. A.Harbourn), Butterworths Scientific Publications,       (1957)

mixtures of volatile compounds have been of great commercial interest to all civilizations for thousands of years. Originally the most important were the essential oils extracted from various plants and subsequently used as perfumes, food flavorings, and for medicinal purposes. Later, with the advent of the industrial revolution, petroleum fractions, solvents and coal products, such as coal tar and benzole mixtures were added to the list. Prior to the introduction of gas chromatography (GC) by James and Martin (1) in the early 1950s, the analysis of complex mixtures of volatile substances was extremely difficult and time consuming to carry out.   At that time, the only effective procedure for separating and analyzing such materials was by distillation using (what was then) high efficiency fractionating columns which, due to their very long equilibrium times, many days (sometimes weeks) were necessary to complete a separation. In addition, the distillation process was only really