[born2dive00]

Hello all

I have a quick question, I am trying to find out the amount of citric acid in diet pepsi. Now this is relatively easy for soft drinks that do not have phosphoric acid such as 7up, and sprite, using sodium hydroxide NaOh.

However if I understand my limited chemistry correctly, NaOH will react with the both the citric acid forming tri sodium citrate, and the phosphoric acid forming Tri Sodium Phosphate is this correct?

If this is correct what do i do to seperate these 2 acids to determine only the amount of the citric acid?

Please let me know, the simpler the better
Thanks
Brad

[Borek]

Not trivial at all.

You can determine sum of the acids with titration and then either citric acid (no quick idea how) or phosphoric acid (by precipitating it).

[Corribus]

As a rough concept, I would take advantage that the first ionization of one is about 10 times more efficient than the other (pKa citric acid ~3.15, pKa phosphoric acid ~2.15. Create a situation where one is ionized and the other isn't, and then exploit that as a means of separation (e.g., through a membrane).