Teledyne GC-Pro/FID - Gas Chromatograph - Manual (Page 21)

GC-Pro FID Operational Theory
Teledyne Analytical Instruments 7
Operational Theory
2.1 Introduction
The GC-Pro FID Analyzer uses a Flame Ionization Detector (FID)
and a Gas Chromatograph (GC) Column to separate and analyze
different factions of a volatile hydrocarbon sample. Using a carrier gas
and a microprocessor actuated switching valve, a fixed volume of
sample is pushed into the Column maintained at a constant temperature.
The eluted gas is analyzed for benzene or other specific analyate
configured for your specific application in a FID detector and the
column is back flushed to accept the fresh sample for the next cycle.
Actual separating and detecting sequence may vary depending on
compounds of interest in the application for which the analyzer is
configured.
The Flame Ionization Detector was selected for use in the GC-Pro
FID Analyzer based on the positive performance and extensive
experience in the use of this detector in other Teledyne analyzers. The
FID has proven itself to be a rugged, stable, long life sensor giving years
of trouble free operation in various applications. Also considering the
fact that the required sensitivity of 100 ppb full scale was achieved, FID
was considered a better choice over the limited life and less reliable
Photo Ionization Detector.
A stainless steel packed column containing Chromosorb Diatomite is
used at a constant temperature of 70°C. Using nitrogen as a carrier gas
and a 5 ml sample loop, benzene elutes from the column within a few
minutes. Additionally, a clear separation is observed from other
aromatic hydrocarbons, namely toluene, ethyl benzene, and xylenes. The
actual temperature setpoint and compound separation for your
instrument may be different depending on the application. It is listed in
the Addendum and Testing Results section of Appendix C.