5 Micro GC Channels
Backflush Option
Agilent 990 Micro GC User Manual 75
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.
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 Figure 28 on page 76.
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 Figure 27.
Figure 26. Natural gas analysis
1 = Methane
2 = Ethane
3 = Propane
4 = iso-Butane
5 = Butane
6 = iso-Pentane
7 = Pentane
Natural gas analysis, straight Natural gas analysis, with backflush at eight seconds
8 50 s 8 50 s
123 45
6
7
12
3
4
5
Figure 27. Backflush system normal flows
Precolumn
Analytical
column
Detector
Injector
Backush
vent
Restriction
Pressure
regulator
System
pressure
Pressure point
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