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|Title:||STUDIES ON ION-EXCHANGE MEMBRANES AS ION-SELECTIVE ELECTRODES|
|Abstract:||Ion-selective electrodes have been the subject of wide spread interest for analytical chemists recently as they permit rapid, accurate and low-cost analysis. Moreover, analysis by these electrodes is non-destructive and adaptable to small sample volumes. Ion-selective electrodes find applications in various industrial and biologically important fields, viz., in ion-monitoring and in the analysis of sea water, glass, soils and its suspensions, nuclear fuels, industrial effluents and pharmaceutical compounds. Such electrodes are normally classified as (i) liquid-membrane electrodes and (ii)solid membrane electrodes, according to the physical state of the membrane. In view of great importance of ion-selective electrodes, some anion and cation-selective electrodes of liquid and solid membrane types have been prepared and their performance investigated. The estimation of perchlorate is difficult in presence of various ions as all the methods are susceptible to interference from halides and reducible substances. Therefore, it was thought desirable to develop a perchlorate-selective electrode. For this purpose, berberine (an alkaloid) was chosen for the preparation of berberine-perchlorate ion exchanger. -4 A 10 M solution of the exchanger in nitrobenzene was used as liquid-membrane. The electrode exhibits a Nernstian response -4 to perchlorate in the range 1.0-10 M with an anionic slope 11 of 57 mV decade"1 of activity. It has faster response (15-50s), wide pH range (1.0-13.0), and good selectivity for perchlorate over other anions. Only permanganate causes significant interference. The electrode has been used to determine perchlorate in presence of halides, nitrate, sulphate and chlorate. This electrode is superior to the electrodes reported in literature from selectivity point of view. In continuation of this work, we have also prepared some more perchlorate-selective electrodes of liquid membrane type by incorporating the ion-pairs of perchlorate with brucine, cinchonidine and emetine (all alkaloids), and zephiramine (benzyldimethyltetradecylammonium chloride) in nitrobenzene. These electrodes also showed comparable performance characteristics to the existing electrodes with regard to -4 potential response range to perchlorate (1.0-5.0x10 M), pH range (1.5-8.0) and response time. Of the four electrodes, one developed with zephiramine-perchlorate was found to be the best in view of its faster response (15-40 sec.) and slightly wider pH range (1.0-9.0). The electrodes based on brucine-, emetineand zephiramine-perchlorate ion-exchangers have also been applied successfully to the direct potentiometric determination of perchlorate in presence of halides, nitrate, sulphate and chlorate. The liquid-membrane electrode of cinchonidine-perchlorate, showing comparatively poor selectivity for perchlorate in comparison with other ions, could not be Ill used for the purpose of estimation of perchlorate in presence of other ions. It could only be used for the determination of perchlorate in pure sample solutions by direct potentiometry. The literature reveals that several periodate-selective electrodes have been prepared and used to determine uC-diols, o<-amino alcohols, carbohydrates and hydrazines. But none has been used to determine periodate in presence of iodate and bromate which cause interference in the gravimetric method of determination. Therefore, it was considered important to develop a periodate-selective electrode that could be used to determine periodate in presence of iodate and bromate. Berberine- periodate ion-pair complex dissolved in O-nitrotoluene was used as liquid membrane. The electrode was found to have a linear response to periodate in the range f 10-1-5.0xl0_5M with an anionic slope of 62 mV decade of activity. It has a fast response (5-10 sec), wide pH range (1.5-7.5), and good selectivity for periodate over other inorganic and organic anions. The electrode has also been employed for the direct potentiometric determination of periodate in presence of iodate and bromate. The estimation of surfactants is important in view of their presence in various effluents. They are usually estimated spectrophotometrically after interacting them with dyes. A convenient method has been developed to estimate cationic surfactants by titrating them with anionic dyes and determining o IV the end point by using ion-selective electrodes. Liquid-membrane electrodes for cetylpyridinium chloride and cetyltrimethylammonium bromide surfactants were prepared by incorporating the the ion-pair complexes of these surfactants with congo red and methyl orange in nitrobenzene. These selective electrodes do respond linearly to these surfactants in concentration range 5.0xl0_4 -10~7M, but the potentials generated are not highly stable. Therefore, cetylpyridinium chloride and cetyltrimethylammonium bromide could not be estimated by using calibration graph method. Therefore, these surfactants were estimated by titrating them with congored, methyl orange and sodium picrate as titrants using these surfactant-sensitive electrodes as indicator electrodes. The error in estimation of these surfactants was found to be 1-2%. The critical micelle concentration (c.m.c.) of these surfactants were determined and found to be in close agreement with those of the literature values. Inorganic ion exchangers, viz., stannic ferrocyanide, titanium tungstate and bismuth tungstate have been used to prepare solid membranes using 30% Araldite as binder. The studies with these membranes have shown that they respond to Ni2+, Co2+ and Pb2" ions over a wide concentration range of 1.0-5.0 x 10_4M, 1.0-5.0xl0~ M and 1.0- 10_4M, respectively. These electrodes also function over wide pH-range. As such they could be used to estimate the abovementioned ions in solutions.|
|Appears in Collections:||DOCTORAL THESES (chemistry)|
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