By Anonymous on Sunday, June 6, 2004 - 06:09 pm:
Hello,
Does the resolution between two compounds change with their concentrations?
Thank you
By Anonymous on Sunday, June 6, 2004 - 07:10 pm:
If the injection is low - no, if the injection is high - yes.
By Anonymous on Monday, June 7, 2004 - 06:56 am:
because of saturation??
jin
By Anonymous on Monday, June 7, 2004 - 08:13 am:
Yes
By Ina on Monday, June 7, 2004 - 04:34 pm:
Hello Anon,
You mean that the width of the peak doesn't change with the quantity of the analyt under over loading limit?
Thanks
Ina
By Anonymous on Monday, June 7, 2004 - 05:24 pm:
You may want to look at the thread "Effect of concentration on plate height". What was discussed there is essentially the same as the question you are asking.
If you look at the van Deemter equation, there is nothing that indicates that peak width should depend on mass (or concentration). So there will be no effect of concentration on peak width - and therefore resolution - if the contribution of the *extra chromatographic factors* are not significant. These would include injection volume, mass on column in case of overload, and the effect of a sample solvent that is chromatographically stronger than the mobile phase.
By Lime on Tuesday, June 8, 2004 - 05:41 am:
Hi,
I think peak shape ( especially tailing )is related to conc. At least for high conc. Otherwise overload conc. wouldn't be such a big problem for peak shape.
Anyway if tailing factor increases, peak width increases and peak width and resolution are non-proportional
By Anonymous on Tuesday, June 8, 2004 - 05:11 pm:
I would agree that you might see less tailing at higher concentrations. In very simplistic terms I think this is because at higher concentrations there are many other analyte molecules which can "knock" bound analytes off of the sites to which they are stuck.
But again, this is a complicating factor. In the absence of all such complicating factors there should be no relationship between peak width and concentration.
By Anonymous on Tuesday, June 8, 2004 - 06:24 pm:
I notice that retention time changes with the concentration of the analyte.
By A.Mouse on Tuesday, June 8, 2004 - 07:23 pm:
The van Deemter equation applies to non-overloaded peaks, and is completely irrelevant for the question, which was about the resolution with increasing concentration. At low concentrations, there is no effect, but at higher concentrations (once the column becomes overloaded) the resolution changes with increasing load.
By tom jupille on Tuesday, June 8, 2004 - 11:01 pm:
I think we may be talking at cross-purposes here.
If you are not overloaded (i.e., if k' does not change as a function of concentration), then peak width will not change as a function of concentration.
If you are overloaded (i.e., if k' *does* change as a function of concentration, then peak width *will* change as a function of concentration.
Here's a "quick and dirty" pdf to illustrate why:
http://www.sepsci.com/temp/overload.pdf