Any Rule of Thumb for Peak Fronting

[carls]

I fully agree with Carl, as my experience goes right in this direction: low ionic strenght in buffers in IEC causes "strange" peak behavior.

I agree with both of you that low ionic strength can alter pH "local" pH if we have mass overload, but recall that if we are dealing with an strong anion exchanger, it's behaviour should be independent of pH. So still the fundamental reason of low ionic strength eluent showing strange peak shape stands unclear.

If the local pH is changed the eluant species in competition with the analyte could change. In the case of a carbonate buffer, if the analyte zone causes a decrease in pH this will increase the bicarbonate ion concentration which is a weaker displacing ion (also lower ionic strength).

[M. Farooq]

I fully agree with Carl, as my experience goes right in this direction: low ionic strenght in buffers in IEC causes "strange" peak behavior.

I agree with both of you that low ionic strength can alter pH "local" pH if we have mass overload, but recall that if we are dealing with an strong anion exchanger, it's behaviour should be independent of pH. So still the fundamental reason of low ionic strength eluent showing strange peak shape stands unclear.

If the local pH is changed the eluant species in competition with the analyte could change. In the case of a carbonate buffer, if the analyte zone causes a decrease in pH this will increase the bicarbonate ion concentration which is a weaker displacing ion (also lower ionic strength).

One more interesting thing is that, even if we assume, eluent species change of carbonate to bicarbonate, we should see tailing not fronting. I see fronting. Bicarbonate alone shows clear tailing.

[carls]

Bicarbonate at what pH and concentration shows tailing?

[M. Farooq]

Bicarbonate at what pH and concentration shows tailing?

It is 25 mM bicarbonate in water. pH would be around ~7-8.

25 mM carbonate also shows tailing. The only thing which is unresolvable is the fundamental (theoretical) reason as to why fronting occurs with low conc of carbonate (~ 2.5-10 mM) with Br. The rest of eluents always produce tailing always produce tailing: 10 mM NaOH, 15 mM NaOH, 32 mM borate, 32 mM acetate?

You can see it is pretty much pH independent effect.