Yokogawa GC8000 Process Gas Chromatograph - Manual (Page 431)

<Appendix A Principle of Gas Chromatograph>
App.A-2
IM 11B08A01-01E
 Component Separation Using Column
Four types of column are available for the GC8000 Process Gas Chromatograph: a packed
column, micro packed column, mega-bore column and capillary column.
Packed columns consist of a stainless steel pipe with a diameter of 2 mm filled with a bulking
agent called a stationary phase. Micro packed columns consist of a stainless steel pipe with a
diameter of 1 mm. Bulking agents are porous polymer, alumina, or diatomite carrier impregnated
with a liquid phase.
Capillary columns use a hollow pipe with a diameter of 0.1 to 1 mm. Those with a diameter of
0.45 mm or larger are called mega-bore columns. As the stationary phase, the inner face coated
with liquid phase, micro-particle of porous polymer or alumina supported, or diatomite carrier
impregnated with a liquid phase is used.
The components in the multi-component gas mixture sample with carrier gas, which is called
the mobile phase, move through the column, repeatedly dissolving into and eluting from the
stationary phase at a certain cyclic rate conforming to a fi xed partition coeffi cient* that is unique to
each component.
* Partition coeffi cient: The concentration ratio of the components, calculated by dividing the component concentration which is in
equilibrium in the stationary phase by the concentration which is in equilibrium in the mobile phase.
Figure 2 shows a diagram of how the multi-component gas mixture is led to a column and
separated into its discrete components over time.
F_A02.ai
Multi-component
gas mixture
Sampling
(1st round)
(2nd round)
Detector Concentration signal
A
B
C
(Intake) (Outlet) Column
Injection
Time
Carrier gas
Carrier gas
:Component A, :Component B, :Component C
Figure 2 Separating Components Using a Column
 Detector
The components separated in the column are led to the detector where the concentration of each
component is measured.
The GC8000 Process Gas Chromatographs can be fitted with thermal conductivity detectors
(TCD), flame ionization detectors (FID) or flame photometric detectors (FPD). The thermal
conductivity detector can measure almost all non-corrosive components but sensitivity is relatively
low. On the other hand, the hydrogen flame ionization detector can measure hydrocarbon and
the fl ame photometric detector can measure sulfur compounds, respectively with high sensitivity.
2nd Edition : May 11, 2012-00