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Ion pairing and acid dissociation constants in poly(vinyl chloride)‐based ion‐selective electrode membranes
Author(s) -
Verpoorte Elisabeth M. J.,
Chan Andy D. C.,
Harrison D. Jed
Publication year - 1993
Publication title -
electroanalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.574
H-Index - 128
eISSN - 1521-4109
pISSN - 1040-0397
DOI - 10.1002/elan.1140050920
Subject(s) - chemistry , membrane , dissociation (chemistry) , dissociation constant , ion , vinyl chloride , benzoic acid , inorganic chemistry , solvation , chloride , analytical chemistry (journal) , organic chemistry , biochemistry , receptor , copolymer , polymer
Ion pairing and acid dissociation constants, as well as limiting conductances, have been estimated in ion‐selective electrode membranes based on a 33 wt% poly(vinyl chloride) (PVC), 66 wt% dioctyladipate matrix using the Fuoss equation of conductance for weakly dissociable species. Dissociation constants of 1.66, 3.51, and 0.69 × 10 −5 were determined for NaClO 4 , C 6 H 5 COOK (KBz), and benzoic acid (HBz), respectively, in a membrane matrix with 1% valinomycin and 0.01% KB(C 6 H 5 ) 4 present as additives. The first two values are consistent with tight ion pairing in a low dielectric solvent and indicate no special role for PVC in ion solvation. The weak acid dissociation is 4 to 5 orders of magnitude higher than expected; HBz also shows unusual interactions with the membrane matrix at low added concentrations. The effect of HBz and methylbenzoate (MeBz) on surface charge transfer resistance and membrane bulk resistance shows that HBz is dissociating to form ions, and a possible mechanism for the unusual interactions has been deduced. MeBz caused a significant increase in surface charge transfer resistance, indicating a mechanism by which membrane permeation by lipophilic, neutral components of biological samples could degrade sensor performance.