Evaluation of a PVC‐Based Thionine‐Zeolite and Zeolite Free Membranes as Sensing Elements in Ion Selective Electrode

Abstract

The construction and performance characteristics of thionine electrodes based on the ion-pair complex thioninetungstophosphate and thionine-mordenite zeolite embedded in a polyvinyl chloride (PVC) matrix is described. Thionine electrode based on the ion-pair is used for the indirect determination of ascorbic acid by standard addition method.Keywords: Thionine-tungstophosphate(TH-TP), Thionine-mordenite, Ion selectiive electrodes, Ascorbic acidThe incorporation of zeolites into electrochemical systems has received increasing attention during recent years. Advances in the modification of electrode surface with zeolites have been extensively reviewed by Rolison [1] and Walcarius [2,3]. Zeolites due to their precisely uniform crystal lattice with pores of molecular dimension, into which guest molecules can penetrate, possess outstanding potentialities for use in electroanalytical measurements.The unique properties of zeolites have been utilized for developing zeolite modified voltammetric/amperometric electrodes exhibiting enhanced selectivity [4,5]. On the other hand, the ion exchange properties of zeolites make them an inevitable candidate for preparing ion-selective membranes for potentiometric cation sensing. The first report on the use of a zeolite-based membrane electrode is that of Marshall [6] who dispersed zeolite particles within an insulating cement matrix. Later, Barrer and James [7] exploited the size selectivity of zeolite A in rejecting the tetraethylammonium cation (too large to fit inside the microporous structure [8]), by preparing membranes made of zeolites embedded in thermoplastic resins, and applying them for the selective detection of sodium ions over tetraethylammonium species. Johansson et al. [9,10] have reported the impregnation of mordenite-type zeolite pellet with low viscosity epoxy resins. The resulting membrane was then successfully applied to the detection of cesium ions, with a significant selectivity relative to the other alkali metal cations and some divalent species. Baker et al. [11] and Demertzis et al. [12,13] investigated the influence of the epoxy resin phase on the main characteristic properties of a potentiometric zeolite electrode, which was reported to be sensitive to alkali metal and other metal cations without a remarkable selectivity of any cation. The electrodes based on the incorporation of zeolite particles into polydimethylsiloxane membranes were applied by Matysik et al. [14] to the potentiometric detection of alkali-metal cations. Potentiometric investigations in non-aqueous media using pressed zeolite disks were described by Dryfe et al. [15]. Recent advances in the potentiometric application of zeolitemodified electrodes includes construction of a disposable electrode for determination of surfactants [16] and an enzymatic biosensor incorporating zeolite for determination of urea [17,18].Thionine is a cationic dye and can fill in the zeolite channels by an ion exchange method [19,20]. Thionine, is an antimethemoglobinemic agent and an antidote to cyani...

Unique potentiometric detection systems for HPLC determination of some steroids in human urine

“…They are resistant to ACN containing HPLC eluents. Montmorillonite electrode (montmorillonite glassy carbon electrode (MM_CW) or montmorillonite graphite/PVC composite electrode (MM_Comp)): the coating material contains 5% montmorillonite, 30% PVC, and 65% DOS [35]. The 3 mL THF was added to a 100 mg amount of this mixture.…”