Ion selective part of an apparatus for the determination of the

Abstract

Ion selective parts are described which comprise a polymeric material, an ion selective component and optionally furthermore a plasticizer and which ion sensitive parts are suited for the determination of the concentration or activity of ions in liquid media. The polymeric material of said ion sensitive parts is a copolymer in which 5-25 mol-% of the monomeric units of said copolymer are substituted with one or more hydrophilic substituents which are selected from the group comprising hydroxy groups, carboxylic acid groups, sulphonic acid groups and phosphonic acid groups. The inventive ion selective parts have, compared with corresponding ion selective parts in which the polymeric material is free of the stated hydrophilic groups or has a lower content of said hydrophilic groups, a better stability of the standard potential E.sub.o and a lower asymmetry potential or no asymmetry potential at all. Said properties of the inventive ion selective parts are also maintained after the corresponding parts had been in contact with solutions which contain organic substances having a higher molecular weight, like proteins. The inventive in selective parts, accordingly, can be used in apparatuses for the determination of the concentration of ions in clinical fields of application, like for instance the determination in whole blood, blood serum or blood plasma.