By davoh on Sunday, February 4, 2001 - 08:51 pm:
Hello!
I have been trying to perform a GC assay method. However, I had some problem and question.
The method is descripted as followed.
GC system : HP 6890
column : 0.53 mm i.d. x 30 m, 1um
flow rate : 45 ml/min
carrior gas : Nitrogen
I wonder the flow rate is right. I have known that the high flow rate is used at packed column and usually at capillary column, the flow rate is 20-30 cm/sec using Helium. So How can I use the flow rate(45ml/min) at my system (PE autosystem XL, using the same column, with Helium gas)?
By jclark on Monday, February 5, 2001 - 05:31 am:
The optimum linear velocity for nitrogen is in the range of 10-15 cm/sec; for helium around 20 cm/sec and for hydrogen well over 30 cm/sec. You can see that for tough separations where theoretical plates are a concern, nitrogen will take a very long time to accomplish a separation. This is the reason that helium is in such widespread use as a carrier gas.
By Ron on Monday, February 5, 2001 - 06:01 am:
Your flow rate is much too high. For the column you are using common flow rates are from 4 to 10 mL/minute when helium is used, depending on the analysis to be performed. Nitrogen flow rates should be lower. If you do not have adequate resolution now, lower your flow rate and try again. If you need faster analysis, try a shorter column with a smaller diameter.
By pierre philippe GARRY on Wednesday, February 7, 2001 - 05:13 am:
There is a downloadable small soft on agilent website very usefull to do all this velocity, pressure calculs for all kind of gaz.
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