eluotropic strength coefficient of mobile phase??

[rick1112]

Hi

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

Thanks a lot

[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:

Effectively, increases in k greater than ~ 5 gives the least reward with respect to increasing resolution. In general the selectivity term is the strongest.

[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

[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.

[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...

[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