The membrane potential of a weakly amphoteric polymer membrane was mea
sured by varying the dissociation state of the dissociative groups wit
hin the membrane through control of the pH of the outer aqueous soluti
on, and the effective charge density of the membrane was evaluated. On
the basis of a modification of the Teorell-Meyer-Sievers equation, we
concluded that the difference between the charge densities of the pos
itively and negatively charged dissociative groups seemed to play an i
mportant role in the permeation behaviour through the membrane. From t
he results of a study of the potentiometric behaviour of aqueous polya
mphoteric solutions, it was confirmed that the ratio of the effective
charge density to the net value could be estimated to be the same as t
hat found previously. (C) 1996 Elsevier Science Ltd.