5 Micro GC Channels
Tuning the backflush time
80 Agilent 990 Micro GC User Manual
Tuning the backflush time
To set the proper backflush time for each new backflush to detector channel, follow either the
“8 m 5CB BF2D procedure” or the “10 m Al2O3/KCl BF2D procedure” on page 81.
8 m 5CB BF2D procedure
1 Set backflush (BF) time to 0 seconds. Start a run to obtain the peaks of all eluted components.
Record the retention time (RT) of n-pentane and 2,2-dimethylbutane.
2 Set run time to a value which is 10 seconds longer than the RT of 2,2-dimethylbutane. Set BF
time to 5 seconds. Start a run again.
3 Increase BF time by 0.5 seconds steps, and start a run. Observe the peak height of
2,2-dimethylbutane. Continue increasing BF time until the 2,2-dimethylbutane peak is
observed (peak height > 3 µV).
4 Finely tune the BF time, find the data point when the 2,2-dimethylbutane peak is observed.
Decrease BF time by 0.1 seconds steps, and start a run until the peak disappears (peak height
< 3 µV). Set BF time for this channel to that value minus 0.2 seconds. A typical “clean cut” time
range of 8m 5CB BF2D channel is approximately 0.3-0.5 seconds. (See Figure 32.)
Table 23 8 m 5CB BF2D settings
Parameter Settings
Column pressure 150 kPa
Injection temperature 110 °C
Column temperature 72 °C
Injection time 40 ms
Run time 90 s
Sample gas NGA gas
Figure 32. 8m 5CB Column for natural gas analysis
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