[wildburg88]

I was wondering if someone could fully explain how to "azeotrope off" ammonium bicarbonate.

If I have a peptide solution in (NH₄)HCO₃ that I then dry down in a SpeedVac / lyophilize, the ammonium, because it is volatile will blow off leaving the bicarbonate in the sample. If I then had 50/50 H₂O/MeOH to the completely tried down sample and lyophilize again and repeat this step 1-2 more times, my sample should be almost completely free of any salt.

How exactly does using 50/50 H₂O/MeOH get rid of the bicarbonate? The sample is not being heated in the SpeedVac, which is kept at 4°C. Is it something like azeotropic distillation?

[Borek]

the ammonium, because it is volatile will blow off leaving the bicarbonate in the sample

Try to write reaction equation.