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
