INFICON 3000 Micro GC Gas Analyzer Operating Manual - Manual (Page 40)

3 - 10
PN
07
4-
51
9-
P1
C
3000 Micro GC Operating Manual
3.3.3.4 Backflush Injector
The backflush assembly consists of:
 a backflush injector
 a precolumn
 an analytical capillary column
The precolumn is a short section of column, whereas the analytical column is
usually longer. The precolumn and analytical column are connected in series.
The precolumn functions to prevent contaminants from entering the analytical
column. The sample first travels through the precolumn and then through the
analytical column. After components of interest enter the analytical column, the
flow is reversed through the precolumn, flushing the unwanted components to vent.
This backflushing of the precolumn prevents these contaminants from entering the
analytical column and causing deactivation or ghost peaks.
The backflush injector has two method parameters in EZ IQ software: Backflush
Time (in seconds) and Inject Time (in milliseconds). The Backflush Time
parameter on the Instrument Setup window can be changed to suit analysis
needs. Valid settings for the Backflush Time are between 0-240 s. Recommended
settings for the Backflush Time are between 6-12 s. Valid settings for the Inject
Time are between 0-250 ms.
The backflush injector can also function in a semi-fixed mode. An Inject Time of
0 ms results in a fixed volume injected and is best used for component levels from
0.1% and higher. This will result in higher precision.
The backflush injector can function in a variable volume mode. An Inject Time
greater than 10 ms will result in a higher injection volume. This used for component
levels below 0.1%.
Actual inject volumes are typically a few microliters of gas. For better sensitivity, set
a higher Inject Time, however, accuracy and precision will be negatively impacted.
Backflush times vary with column and setpoints and must be optimized for every
3000 Micro GC module.