Chromatography Forum

Hello,

I have a quick question on non-linear (Langmuir) kinetics vs. linear kinetics for an analyte partitioning into a stationary phase. I've seen from a few older papers on the theory of frontal affinity chromatography that if an analyte has a high concentration, one can obtain Langmuir kinetics due to retention (or breakthrough) time being dependent on the concentration of the analyte, i.e. concentration-dependent migration. I was wondering if this was true for flow rates as well? For example, if an analyte at high concentration is observed to behave in a non-linear fashion, can you change the flow rate (either to faster or slower flow rates) to get back to linear kinetics, or is the concentration of the analyte the only factor that decides if you have non-linear or linear kinetics? Thanks for any help you could give.
Mike

A departure from the linear part of the Langmuir isotherm has nothing to do with kinetics. It is rather a question of the number of sites that are available for interaction. In affinity chromatography, one often has only a limited number of sites. If this is what your question was, then changing the flow rate makes no difference (well only a little bit of difference due to mass transfer).