Ion pair extraction titration

ON WHICH PRINCIPLE?

Therefore, in our case and when it comes to tutorials, a mixed indicator will be used (I amine colored indicator, IH+ amine colored and protonated indicator) as well as an acid buffer at pH=2.8.

The principle of this assay:

diagram of the principle of the assay : step 1 : addition of the acid buffer at pH 2.8, step 2 : addition of DOSS, step 3 : addition of DOSS, step 4 : formation of the ion pair between the protonated amine and DOSS, step 5 : formation of a second ion pair between the protonated colored indicator and DOSS in excess

The amine of the active ingredient is directly assayed, without prior extraction, by ion pair formation with DOSS (dioctyl sodium sulfosuccinate). In the presence of a pH=2.8 buffer, the amine is in the form of a salt soluble in the aqueous phase together with the color indicator (2). By the addition of a DOSS solution, an ion pair forms between the amine and DOSS [(4, 5) the most stable ion pair at this pH] which is insoluble in the aqueous phase and passes into the organic phase. At the end of the assay (6) when all of the amine has been paired, an excess of DOSS combines with the indicator (less stable ion pair) that turns from green to dirty grey and finally mauve (color of the turn).