Sensitive Ionization System for the Detection of Permanent Gases and Organic Vapours by Gas Chromatography

Journal/Book: Reprinted from Nature Vol. 197 No. 4867 pp. 625-626 February 9 1963. 1963;

Abstract: Yale University School of Medicine New Haven II Conn. THE two most commonly used high-sensitivity detection devices for gas chromatography the ´flame ionization'1 and the ´argon ionization' detectors2 are insensitive to permanent gases. During an investigation into the various mechanisms responsible for ionization phenomena within the latter class of devices it was noted that under certain conditions of field and radioactive source strength detector geometry and operating temperature a simple ionization system using argon as carrier gas could be utilized to detect extremely low concentrations of permanent gases. The Limit of sensitivity of this new mode of detector operation is up to 1 000 times greater than that reported with an earlier device3. In addition to this extraordinary response to fixed gases this Same detector when operated at a different potential was found to retain certain characteristics including the high sensitivity toward organic molecules as that noted by Lovelock2 for the conventional small ´argon detector'. The particular ionization chamber which provided optimal results is of an annular design as shown in Fig. 1. The outer cathode is a brass cylinder the internal dimensions of which are 10 mm wide and 10 mm high. The central anode is a solid brass rod 8 mm in diameter and 10 mm high insulated from the cathode by polytetra-fluoroethylene and containing two 1/16-in. dia. orifices which serve as gas inlets. The source of radiation is provided by a 200 mc. tritiated titanium foil (28 mm long x 10 mm wide) which snugly fits against the wall of the cathode. The total volume of this particular version of detector is 280 µl. While operating the device between 150° and 225° C an investigation of the effect of variation in the applied field an the response to known volumes of permanent gases revealed an area of high sensitivity with a maximum occurring between 1-2 V (field strength = 10-20 V/cm.). At these low voltages (conveniently available from either a battery or a closely regulated power supply) all gases examined (He Ne CO CO2 H2 O2 N2 CH4 C2H4 C2H6) when passed through the detector provided an increase in current. At 165° C with an applied voltage of 1·34 V and pure argon flowing through the chamber the standing current was 3·7 x 10-9 amp-about 1/2 of the saturation current obtained at 100 V. The noise-level was low at 1·2 x 10-13 amp. The minimum limit of detectability of these gases under the stated conditions is given in Table 1. No appreciable change in sensitivities were observed as the temperature was varied from 150° to 225° C. ___MH

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