Electron Capture Detector (ECD):
The characteristic features of an ECD are as follows:
i) Specific
ii) Selective to halogens
iii) Sensitive to a few parts per trillion
The electron capture detector measures the loss of signal rather than a positively generated electrical current. As the nitrogen carrier gas flows by the detector, a tritium or Ni63 source ionizes the nitrogen molecules and slow electrons are created. The slow electrons migrate to the anode under the fixed voltage that is created as "cell voltage". The slow electrons generate a steady current. If a sample holding electron absorbing solutes is introduced, this current will be decreased. The loss of current is a measure of the amount and electron affinity of the solute.