Measuring the flow rate

Chromatography Forum: GC Archives: Measuring the flow rate
Top of pagePrevious messageNext messageBottom of pageLink to this message  By M. Perez on Friday, August 27, 1999 - 04:41 pm:

Which is the best temperature to measure the column flow rate or linear velocity? Is it correct if I take it at the (or near to) analysis temperature? Thank you very much for your advices.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Scott Fredrickson on Friday, August 27, 1999 - 05:32 pm:

Yes, that is the best place. If you are running a temperature program over a wide range, the flow will drop dramatically as the temperature goes up. Hewlett-Packard built their programmable electronic flow controllers to solve the problem, and has useful data on the topic.

Most of us are lazy, or it is difficult or time-consuming to take accurate readings at the analysis temp, so you won't see 'flow rate at X temperature' in methods very often. And usually, it doesn't matter that much, as long as you are happy with the analysis, and can reset the same flow the next time you need to run that analysis.
As long as you document the measurement temperature, it probably doesn't matter where you take it. When trying to match method parameters, we usually try to approximate retention times at the suggested temperature by adjusting flow. It's simpler, and usually works fine.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Stan on Tuesday, September 7, 1999 - 05:37 pm:

I find most column specs are given with the linear velocity taken at the beginning of the temp program. Although as Scott says, the flow will drop as the temperature goes up, for troubleshooting purposes, the linear velocity should be measured at the beginning or ambient column temperature


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Wilhelm Leung on Friday, September 24, 1999 - 07:12 pm:

The linear velocity or flow rate is normally measured at the setup conditions i.e. the column temperature for isothermal or the initial temperature of the temperature program. This is the convention adopted in most official methods.


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