A method is described which allows the direct measurement of conditional Ion-pair extraction constants K\. By use of a recently described filter-probe membrane phase separator the necessary extractions and absorbance measurements are conveniently and rapidly made on a continuous flow basis as a function of varying aqueous phase pH. The technique Is used to characterize the extraction of the cationic conjugate acids of the drugs promethazine, codeine, and diphenhydramine with plcrate reagent and of the latter also with the reagent diplcrylamlnate.
The "filter-probe" membrane phase separator is used with a gravimetric buret to obtain the following constants at 25 °C by measuring solvent-extraction isotherms: dimerization constant of benzoic acid in chloroform (log K2,HBz = 2.12 ± 0.01); "self-ion-pair extraction" constant of Naloxone into chloroform [Formula: see text]; and ion-pair dissociation constant of tetraethylammonium picrate in methylene chloride (log Kdiss = −4.52 ± 0.09).
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