The Pulsed Discharge Electron Capture Detector

The pulsed discharge electron capture detector is an extension of the previously discussed pulsed discharge helium ionization detector, a diagram of which is shown in figure 44. The detector functions in exactly the same as that of the traditional electron capture detector but differs in the method of electron production. The sensor consists of two sections: the upper section has a relatively small diameter and is where the discharge takes place. The lower section has a much wider diameter and in this part of the sensor, the column eluent is sensed and electron capturing occurs. As with the pulsed discharge helium ionization detector, the potential across the electrodes is pulsed at about 3 kHz with a discharge pulse width of about 45 msec. The discharge produces electrons and high energy photons and some metastable helium atoms. The helium, doped with propane, enters just below the second electrode, metastable atoms are removed and electrons are generated both by the decay of the metastable atoms and by the photons.

Courtesy of Valco Instruments Company Inc.
Figure 44 The Pulsed Discharge Electron Capture Detector