Page 1 of 1

eluotropic strength coefficient of mobile phase??

Posted: Wed Sep 24, 2008 5:42 am
by rick1112
Hi

What is eluotropic strength coefficient of mobile phase?? How does this affect retention and resolution??

Thanks a lot

Posted: Wed Sep 24, 2008 7:47 am
by JA
I posted about elutropic strength only three days ago.
http://www.sepsci.com/chromforum/viewto ... 9218#43116

For its affect on resolution, consider the equation:
Image
Effectively, increases in k greater than ~ 5 gives the least reward with respect to increasing resolution. In general the selectivity term is the strongest.

Posted: Sat Oct 04, 2008 4:15 am
by rick1112
Hi
I went through your post..some question still remains…taking eluotropic strength of a mobile phase/solvent into consideration how will I select a solvent to be used in mobile phase, lets say I have choice between ACN, Iso-propanol, n-propanol, THF…??? And how this will affect my selectivity/resolution??

(I have read in some article, where they have used a mixture of ACN and n-propanol for better resolution and have stated that this was done taking eluotropic strength into consideration...so this got me thinking on how did they decide??...;will try to get the article…)

Well thanks a lot

Posted: Mon Oct 06, 2008 3:13 am
by Uwe Neue
The selectivity of a separation is a more complex issue than just the retention. I gave it a shot for RP separations in a recent publication in J. Sep. Sci., which I am willing to distribute to those interested. The easiest thing to state is that a manipulation of the mobile phase additive is at least as powerful (if not more powerful) than to change the stationary phase. A few crude and tentative rules can be constructed for different organic modifiers. There is an interaction between the basic type of stationary phase and the effect of the organic modifier.

Posted: Thu Dec 31, 2009 7:26 am
by rick1112
I gave it a shot for RP separations in a recent publication in J. Sep. Sci., which I am willing to distribute to those interested.
Hi..could you please provide me with this article...thank you

stirring up an old topic...

Was going through one article which stated (and i qoute)....the high eluotropic nature of these solvents (i.e propanol,isopropanol or butanol) restricts the selectivity of chromatography separation.

kind of baffled me...because i though eluotropic strength could add on to the selectivity of chromatography separation (plz correct me if i am wrong..)

so please help me to clarify...

Posted: Thu Dec 31, 2009 3:37 pm
by Uwe Neue
There are actually several articles on the subject.

1. U. D. Neue, "Stationary Phase Characerization and Method Development", J. Sep. Sci. 30 (2007) 1611-1627
2. U. D. Neue, A. Mendez, Selectivity in Reversed-Phase Separations: General Influence of Solvent Type and Mobile Phase pH", J. Sep. Sci. 30 (2007) 949-963
3. U. D. Neue, J. E. O'Gara, A. Mendez, "Selectivity in Reversed-Phase Separations: Influence of the Stationary Phase", J. Chromatogr. A 1127 (2006) 161-174