Gas Chromatography Detectors - Ionization Detectors > The Electron Capture Detector > Page 73

The average current is about 1 x 10-8 amp and has an associated noise level of about 5 x 10-12 amp. A diagram of the electron capture detector as developed by Lovelock et al is shown in figure 40.


Their sensor consisted of a small chamber, 1-2 ml in volume, with metal ends separated by a suitable insulator. The metal ends acted both as electrodes and as fluid conduits for the carrier gas to enter and leave the cell. The cell contained the radioactive source electrically connected to the conduit through which the carrier gas enters and to the negative side of the power supply. A gauze "diffuser" was connected to the exit of the cell and to the positive side of the powersupply. The electrode current was measured by an appropriate high impedance amplifier.


An example of a more modern sensor design is that used in the Perkin Elmer electron capture detector and is shown in figure 41.



Courtesy of the Perkin Elmer Corporation


Figure 41 The Perkin Elmer Electron Capture Detector