Detector Systems
Electron capture detector (ECD)
Uncaptured electrons are collected periodically by applying short•term voltage pulses to cell electrodes. This cell current is measured and compared to a reference current, and the pulse interval is then adjusted to maintain constant cell current.
Therefore, pulse rate (frequency) rises when an electron•capturing compound is passing through the cell. The pulse rate is converted to a voltage, linearly related to amount of electron•capturingmaterial in the cell.
Figure
Detector
| Anode Purge Flow | |
| Vent | |
External | Internal | |
Plumbing | Plumbing | |
Final Pressure Regulators | Makeup Gas Adapters | |
Capillary Columns | ||
and Gauges | Only | |
Traps | Flow Manifold Block | |
| PURGE FLOW | |
Capillary | On/Off | |
MAKEUP GAS | ||
Makeup | ||
On/Off | ||
Gas |
Column
Flow Diagram, Electron Capture Detector (ECD)
Thus, the ECD responds to compounds having an affinity for electrons (for example, such halogenated materials as pesticides and related compounds). Table 7•2gives general indication of expected sensitivity to different classes of organic compounds.
138