HP 5890 Series II Plus Reference Manual page 138

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 7-6
Final Pressure Regulators
and Gauges
Traps
Capillary
Makeup
Gas
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
External Internal
Plumbing Plumbing
Flow Manifold Block
Anode Purge Flow
Vent
Makeup Gas Adapters
Capillary Columns
Only
PURGE FLOW
On/Off
MAKEUP GAS
On/Off
Detector
Column