Agilent Technologies 6890 Series, Service Manual, Page: 312 / 867

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Jun 2001
Detectors
Agilent 6890 Gas Chromatograph Service Manual
341 Micro-cell Electron Capture
Detector (
µ
-ECD)
Theory of operation
The Micro-cell Electron Capture Detector
(µ
-ECD), G2397A, is based on the
phenomenon that electronegative species can react with thermal electrons
present to form negatively charged ions. The loss of such electrons is related
to the quantity of analyte in the sample. In order to produce capturable (low
energy) thermal electrons, the carrier gas is ionized by beta particles from a
radioactive source in the cell. This electron flow produces a current, which
is collected and measured. When the sample molecule is introduced into the
cell, electrons which would otherwise be captured at the electrode are
captured by the sample, resulting in decreased current. This change is
recorded and measured for the chromatogram.
Figure 341-1 The Micro-cell Electron Capture Detector (
µ
-ECD)
Pneumatic lines
Detector body (under
cover)
Heater/sensor cable
Vent line
Electrometer
Electrometer ribbon cable