PLASTICIZERS FOR LIQUID POLYMERIC MEMBRANES OF ION-SELECTIVE CHEMICALSENSORS

A variety of 55 different plasticizers based on various structural ele ments were investigated in respect to their applicability in liquid po lymeric membranes of chemical sensors. The plasticizers and the overal l performance of the membrane were judged in respect to the properties of lipophilicity, solubility, exudation and selectivity, respectively . A strategy for the design of plasticizers is derived from theoretica l considerations and verified by experiments. The selectivity data wer e obtained by measurements with a standard Mg2+ selective electrode op timized for clinical applications. A plasticizer needs several large a lkyl and/or aryl residues to exhibit sufficient lipophilicity. In orde r to avoid crystallization or exudation, the use of branched alkyl cha ins as well as the link or the substitution of the structural elements by an adequate number of polar or polarizable groups is encouraged. H owever, to ensure high selectivities, plasticizers should not contain functional groups which may act as coordination sites and therefore co mpete with the carrier. In contrast to earlier publications it was obs erved that other properties than the dielectric constant of the plasti cizer are more important for the selectivity of the membrane. A correl ation between selectivity coefficient and the dielectric constant of t he plasticizer could not be found.