21   J. E. Lovelock, J. Chromatogr. 1(1958)35. 22   J. E. Lovelock, Nature, Lond. 181(1958)1460. 23.  R. P. W. Scott, Nature, Lond, 183(1959)1753. 24.  S. A. Beres, C. D. Halfman, E. D. Katz and R. P. W. Scott,        112(1987)91. 25. J. E. Lovelock and S. R. Lipsky, J. Amer. Chem. Soc. 82(1960)431. 26. A.J.P. Martin and R.L.M. Synge, Biochem. J. , 35(1941)1358. 27. A. T. James and E. A. Piper, J. Chromatogr. 5(1961)265. 28. A. T. James and E. A. Piper, Anal. Chem. 35(1963)515. 29.  S. A. Ryce

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

not reported. It was not apparent whether the associated electronics contained non linear signal modifying circuitry or not. Unfortunately, there were several disadvantages to this detector. One disadvantage was the erosion of the electrodes due to "spluttering" In addition, the electrodes were contaminated by sample decomposition and it was essential that it was used with a well–controlled vacuum system.                                             The Spark Discharge Detector Lovelock [15] noted that the voltage at which a spark will occur between two electrodes situated in a gas will depend on the composition of the gas between the electrode tips and suggested that this could form the basis for a GC detector. The system suggested by Lovelock is shown in figure 49.     Figure 49 The Spark Discharge Detector

current increases to 10-7 amp, this will cause a 300 volt drop across the linearizing resistance of 3 x  109  (10-7x 3 x  109 = 300) and consequently reduce the voltage across the electrodes to 1000 volts. In this way the natural exponential response of the detector can be made sensibly linear. In a typical detector, the primary current consists of about 1011 electrons per second. Taking the charge on the electron as 1.6 x 10-19 coulombs this gives a current of 1.6 x 10-8 amp. According to Lovelock [20], if each of these electrons can generate 10,000 metastables on the way to the electrode, the steady state concentration of metastables will be about 1010 per ml (this assumes a life span for the metastables of about 10-5 seconds at NTP). From the kinetic theory of gases it can be calculated that the probability of collision between a metastable atom andan organicmoleculewillbeabout 1.6 : 1. This would lead to a very high ionization efficiency and Lovelock claims that with sensors

105. An example of the use of a pulsed helium discharge detector for monitoring the separation of some aromatics on a capillary column is shown in figure 37. The pulsed helium discharge detector appears to be an attractive alternative to the flame ionization detector and would eliminate the need for three different gas supplies. It does, however, require equipment to provide specially purified helium, which diminishes the advantage of using a single gas.   The Electron Capture Detector Lovelock's work on ionization detectors culminated in the invention of the electron capture detector (25).  However, the electron capture detector operates on an entirely different principle from that of the argon detector. A low energy b-ray source is used in the sensor to produce electrons and ions. The first source to be used was tritium absorbed into a silver foil but, due to its relative instability at high temperatures, this was quickly replaced by the far more thermally stable 63Ni source

The Logarithmic Dilution Method of Linearity Measurement This method of linearity measurement was introduced by Lovelock (2). The procedure requires some special apparatus that is diagramatically represented in figure 3. Figure 3 The Logarithmic  Dilution Apparatus. A known mass of solute is introduced into a well–stirred vessel through which passes a flow of gas. The exit gas is arranged to pass directly into the detector. As a consequence, the mixture is continuously diluted and the concentration of the solute in the exit flow continuously  monitored by  the detector.   Let a volume