Why not an acid such as acetic acid? That is OTC, and a stronger acid then carbonic acid.
Piping in CO2 till saturation was probably not thought out so well, It popped into my head, thinking, what is a way to reduce the pH value to crash out the ibuprofen, which has a pKa of 4.4. I also dont want to add anything else in the aquarious phase that I cannot remove easily - which fueled the CO2 idea. Once the unwanted is crashed out, I"d need to filter, and then get this baby back to neutral or close too, because low pH is not so good I have heard for this particular molecule
What about plain phosphoric acid, i.e. work out how much I need to bring the pH down to say 3.2 - the ibuprofen would crash out, I seperate via filtering. and then add CaOH to bring the pH back up to what it started as, and the calcium phosphate would also crash out.
Vesp, if I did use the correct amount of acetic acid, and got the pH to around 3, I need some way to remove it, and bump up the pH. Perhaps I need to find out if codiene can indeed cope with pH 3, and with gentle heating, around 40C, the acetic would slowly be removed. I think. Im not sure of course. for this theoretical situation.