Development and applications of Ion-selective electrodes
thesisposted on 04.02.2011, 14:53 by Agha S. Pathan
A new type of liquid state electrode assembly based on a natural rubber membrane and using a graphite rod as internal reference electrode, has been developed for use with organic salts which are soluble in organic solvent. Electrodes have been developed for determination of zinc(II)j perchlorate and tetrafluoroborate ions, using basic dye salts containing those arAons. In general, natural rubber sheeting is treated with a water immiscible organic solvent containing the salt; swollen sheeting is used as the membrane. These electrodes respond in a Nernstian manner, giving a potential-concentration slopes of 29.5,57.5 and 58.5 mV for zinc(II), perchlorate and tetrafluoroborate electrodes respectively. The slope is stable for a reasonable length of time, e.g. potential-concentration slope is decreased by 0.5 W after about three to five weeks, depending on the type of electrode. In the preparation of these electrodes, the choice of solvent and the kind of natural rubber has been carefully selected, as these factors influence the operation of the membrane. Effects of solution pH and the temperature variations on response of the electrodes, have also been studied. Further work also has been done on studying the Gmelin reaction (reaction of nitroprusside and sulphide ions) with a sulphide ionselective electrode. This reaction involves a study of the reaction between nitroprusside and sulphide ions, where nitrosyl group is modified to pentacyanothionitroferrate(II) imparting a purple colour to the solution. For determination of sulphide and nitroprusside by potentiometric titration optimum conditions have been developed. Also a colorimetric procedure for sulphide determination is recommended.