Nitrate Selective Electrodes Containing Immobilised Ion Exchangers

Abstract

A range of ion selectivee lectrodes( ISEs) for the determinationo f nitrate has been producedu sing polymeric membranesc ontainingi mmobilisedq uaternarya mmonium saltsa s the ion exchanger.T he useo f the conventionasl olventc astingt echniqueg ave rise to a relatively low cross-link density, two sided response and poor thickness control. The developmenot f a hot pressingt echniquer esolveda ll thesep roblemsa nd would readily suit large scale manufacturing. In this work poly (acrylonitrilebutadiene)( NBr) was selecteda s the membranem atrix and was robust, gavee nhanced selectivityc oefficientsa nd extendedm embraneli fetime. The beste lectrodef abricated contained6 -5% m /m triallyloctylammoniumb romide,7 -2% m /m dicumyl peroxidea nd 39-7%m/m2 -nitrophenyloctyel theri n a 50% ACN contentN Br polymer matrix. The electrodeh ad a lifetime in excesso f 665 daysa nd the responseto nitratew asN ernstian in the range Ix 10" to Ix 10' mol dm-1 of nitrate. The limit of detection was 4-5 x IW mol dm-1 and the selectivity coefficient k Pot NO,,- - C1 was 5.3 xIW. The immobilised ion exchanger membrane electrode' offered superior lifetime and mechanical strength. The cross-link density of the membranes was determined by solvent swelling and the use of the Flory-Rehner equation. The role of cross-link density upon the electroanalytical properties of membranes was investigated in the range 0-6 x 10' to 11-0 x 10' mol cross-link cm-'. The membranes were studied using electron microscopy and the conditioning process monitored using ion exchange chromatography. Two different response mechanisms were proposed dependent on the membrane composition and the inclusion of solvent mediator.