Thermo Scientific FOCUS GC, Instruction Manual

Page: 158 / 356

Chapter 8
Flame Ionization Detector (FID)
FID Overview
158 Instruction Manual
FID Overview
In the FID, the effluent from the column is mixed with hydrogen and burned in a
stream of air as it emerges from the jet. The jet acts as a polarizing electrode,
while the metal collar surrounding the flame forms the collecting electrode.
A polarizing voltage is applied across the electrodes from the electrometer unit to
accelerate and collect the ions that are generated during the combustion process of
organic compounds. The resulting ionization current is sensed by an electrometer
amplifier and converted to a suitable output signal. Figure 8-1 shows the FID.
Figure 8-1. Flame Ionization Detector
Detector Base Body
The detector FID is easily interchangeable because of base body that acts as a
bridge between the detector and analytical column.
This detector base body, see Figure 8-2, can accept all types of capillary column.
The column enters the detector jet directly to eliminate any dead volumes. The
base body allows columns to be connected using either M4 or M8 mm fittings.