Mechanism of Isocratic elution??

[rick1112]

Hi

Could anyone tell me the binding and elution mechanism in isocratic elution model in reverse phase chromatography.

Thank you

[Bruce Hamilton]

Love binds all....

It would be a really, really good idea to look at the copious amounts of freely-available information available on the WWW, espcially at column suppliers sistes such as Waters, Agilent, Phenomenex, and many other sites listed in the resources section of this site.

Bruce Hamilton

[tom jupille]

I think what Bruce is trying to say is that there is no single "one-size fits all" mechanism. Depending on the details of the analyte, stationary phase, and mobile phase, mechanisms can include hydrophobic binding, liquid-liquid partition (with surface-bound solvent), adsorption (with residual silanols), ion-exchange (with ionized silanols, residual trace cations, or hydrophobic counterions), ion exclusion, and size exclusion (I've probably overlooked a few, but this should do for starters).

[Mark Tracy]

I would suggest R.P.W. Scott's http://www.chromatography-online.org.

[rick1112]

hi
thanks a lot for the reply
i was wondering about the reverse phase condition, how does seperation is possible in isocratic condition between the impurities..?? as in gradient elution condition, the increase in organic phase helps in elution, thus we can control or increase the sepration of impurities by changing the % of organic phase,...but how does one achive this in iscoratic condition??

[Bryan Evans]

Hi Rick -

This article might be helpful for you:

"The Power of Mobile Phase Strength" - John Dolan, June 1 2006

http://www.chromatographyonline.com/lcg ... ?id=335696

[DR]

Generally speaking, retention and elution times are a function of the partition coefficients between the mobile phase and the stationary phase for each analyte you inject onto a column. If the analytes have different partition coefficients under a given set of conditions (column packing, MP, temp), then they will be separated.

[Mark Tracy]

Each substance has a characteristic ratio of affinities for the mobile phase versus the stationary phase. That ratio determines what portion of time a molecule spends stuck to the stationary phase and what portion being swept along by the mobile phase. The ratio is neither zero nor infinite, but some intermediate value. The affinities are partly an intrinsic property of each molecule and partly the result of external influences that the chemist may manipulate.

Now if one learned chromatography by analyzing proteins, one might get the impression that the affinity changes as a step function of the mobile phase composition. (That is, below a threshold, the ratio of affinity is zero, and above the threshold it is infinite.) This is almost true of proteins, but not true in the general case. For small molecules, the ratio is a nicely behaved function (if not always well understood).