What is the optimum flowrate for the column used(1.7m)?

Chromatography Forum: GC Archives: What is the optimum flowrate for the column used(1.7m)?
Top of pagePrevious messageNext messageBottom of pageLink to this message  By Nur Baizura on Friday, January 18, 2002 - 09:36 pm:

The column used measured 1.7 meter. I injected 5ul of toluene at 10,20,30,50 and 70 ml/min carrier gas flowrate. I had obtained a graph of HETP against the gas flowrate.
The results obtained on the graph seems to show that the highest HETP was when the 5ul toluene is injected at 20ml/min gas flowrate. why? But the rest is increasing constantly....


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Monday, January 21, 2002 - 05:57 am:

Are you forced to inject as much as 5uL ? Are your peaks symmetrical? It sounds like you are using a thermal conductivity detector and your column is overloaded. The experiment might give different results if you inject 0.1 uL or less (if you have enough sensitivity).


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Friday, January 25, 2002 - 08:57 am:

The other question to ask is if this is a packed column and if so what is the I.D., this will determine the correct flow rate. And of course on a packed column 5 microliters is not really a very large sample volume.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Tuesday, January 29, 2002 - 09:03 am:

If you look at a van Dempter plot you will see that the column efficiency is determined using linear velocity, not volumetric flow. Any good textbook should be able to answer your question about the shape of the plot.


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