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5
Micro GC Channels
Backflush Option
Backflush Option
Backflush to vent is an advanced technique used to prevent later-eluting compounds from
reaching the analytical column and detector. The main reason for applying this technique is to
keep the analytical column clean, and reduce analysis time.
The Micro GC is optionally available with GC modules that incorporate backflush capabilities.
1 2 3
4 5
8
Natural gas analysis, straight
Figure 26.
Natural gas analysis
A backflush system always consists of a precolumn and an analytical column. The two columns
are coupled at a pressure point, which makes it possible to invert the carrier gas flow direction
through the precolumn at a preset time, called the backflush time. See
The injector, two columns, and detector are in series.
The sample is injected onto the precolumn where a preseparation takes place; injection takes
place in normal mode. See
System
pressure
Pressure
regulator
Figure 27.
Backflush system normal flows
Agilent 990 Micro GC User Manual
1 = Methane
2 = Ethane
3 = Propane
4 = iso-Butane
5 = Butane
6
6 = iso-Pentane
7
7 = Pentane
50 s
Figure
Restriction
Precolumn
Injector
Backflush
vent
1 2
3
5
4
8
Natural gas analysis, with backflush at eight seconds
27.
Analytical
column
Pressure point
50 s
Figure 28
on page 76.
Detector
75
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