Sushma Agrawal

Studies with inorganic ion-exchange membranes.

The pyridinium molybdoarsenate membrane shows a response to pyridinium ions and can be used to determine the concentration of these ions in the range 10(-3)-1M. The potentials generated across the membrane are reproducible and the response time is less than 1 min. There is no interference from certain inorganic and organic ions. The electrode can be used in the pH range 3-6 as well as in non-aqueous medium. Small additions of cetyltrimethylammonium bromide cause large shifts in the membrane potentials. A membrane, after being treated with this surfactant, shows a wider range of response to pyridinium ions. Precipitation titration of pyridinium nitrate has been monitored by using this membrane electrode.

Synthesis and ion-exchange properties of cerium(IV) molybdate

Cerium(IV) molybdate, prepared under the optimum conditions of concentration, acidity etc., shows exchange capacity of 0.96 meq per g of exchanger. The sorption of a large number of metal ions has been investigated and the compound shows promising behaviour as cation exchanger. Numerous separations of analytical and radiochemical interest have been performed on the columns of this exchanger with great efficiency.

Use of chromium ferrocyanide membrane electrode in the potentiometric titration of ferrocyanide with metal ions

Membranes based on the inorganic ion-exchanger chromium ferrocyanide have been prepared, which exhibit linear response to ferrocyanide over the concentration range 10(-1)-10(-4)M. Although the electrode is not very specific for ferrocyanide, it can be used for potentiometric titration of metal ions with ferrocyanide ion or vice versa. Hg(2+), Th(6+), UO(2+)(2), Pb(2+), Cu(2+) and Zn(2+) have been determined in this way.

Membranes of α-picolinium molybdoarsenate in “Araldite” as Tl(I) ion-selective electrode

ZusammenfassungDie Elektrode kann für Tl(I)-Bestimmungen im Bereich von 10−1 bis 10−5 M verwendet werden. Anhand der Bestimmung von Selektivitätskoeffizienten anderer Metallkationen ergab sich keine Störung. Auch zahlreiche Anionen verursachen keine Störung. Die Behandlung der Elektrode mit einem kationischen Tensid (CTAB) wurde ebenfalls untersucht, brachte aber keine weitere wesentliche Verbesserung.SummarySolid membranes of α-picolinium molybdoarsenate in Araldite are evaluated as Tl(I) selective electrode. The electrode can be used for Tl(I) determinations in the concentration range of 10−1 to 10−5 M. Selectivity coefficient values observed for a number of other metal cations show no interference. Various anions tested did not interfere. The response of the electrode was also evaluated after equilibrating it with a cationic surfactant (CTAB), however this did not considerably improve its behaviour.

Thallium(I) Selective Solid Membrane Electrode

Abstract Heterogeneous membranes of 2.0 cm diameter were prepared from a 60:40 mixture of thallium(I) molybdoarsenate and Araldite, These membranes gave near Nernstian response to thallium(I) ions over the concentration range 10−1 to 10−3M but could be used for determination of thallium(I) down to 10−5M. Slope of the log concentration-potential plot is improved in 10 and 25 percent acetone-water mixture. The response was independent of pH over the range 4.0 to 6.0, The response time of the electrode is few seconds and potentials generated are reproducible. The selectivity of the electrode over a large number of cations was studied. The values of selectivity coefficients are of the order 10−2 for monovalent and 10−3 for bivalent cations. Anions did not interfere. Potentiometric-titration of thallium nitrate with potassium chromate was also done using the membrane as an end point indicator electrode.

Sorption behaviour of rubidium, thallium and silver on chromium ferricyanide gel binary separations of Rb+ and Tl+

Sorption behaviour of monovalent Rb+, Tl+ and Ag+ is studied on chromium fericyanide gel. Log Kd vs log concentration plots show that Rb+ and Tl+ are sorbed through ion exchange mechanism in a higher concentration range of ammonium nitrate or nitric acid, whereas the adsorption of Ag+ is irreversible. It was found possible to elute Rb+ and Tl+ on the columns of this gel by 4 mol dm−3 NH4NO3 and 10 mol dm−3 HNO3, respectively. Binary separations of Rb+ and Tl+ from a number of other metal ions were achieved as other ions were found practically unadsorbed on these columns and were eluted with water of pH 2–3. Achieved separations are of radioanalytical and analytical importance.

Synthetic inorganic ion-exchange materials. Part XXXII. Studies on an araldite-based membrane of crystalline antimonic(V) acid as a nitrate ion-selective electrode

An Araldite-based membrane of crystalline antimonic(V) acid, when acting as a nitrate ion-selective electrode, shows a near-Nernstian response for concentrations of nitrate ions between 10–5 and 10–1M and can be used for determining the activity of the ions. Stable potentials are observed within 10–30 s and for about 2 min. The useful pH range is 3.5–11 at a higher concentration (5 × 10–3M) and 4.5–9 at a lower concentration (5 × 10–4M) of nitrate ions. This membrane responds to nitrate ions in a solution containing 25% of nonaqueous solvent.

Chromatographic separations of metal ions on zirconium tungstoarsenate impregnated ion-exchange papers

Abstract A new heteropolyacid salt ion-exchanger, zirconium tungstoarsenate, has been used for preparing impregnated ion-exchange papers. Twenty-nine metal ions have been chromatographed and RF values determined in seven different mixed solvent systems containing 1-propanol and HNO3 or HCl. On the basis of the difference in selectivities for different metal ions on impregnated papers, a large number of binary and ternary separations has been obtained. Some of the important separations achieved are Ag+–Tl+, Ag+–Pt(IV), Zn2+–Hg2+, Sb3+–Bi3+, Zn2+–UO2 2+, Fe2+–Fe3+, Sb3+–Bi3+–Hg2+, Ag+–Ba2+–UO2 2+, and Ag+–Zn2+–Cu2+–Sn2+. The results are compared with those obtained on plain papers.

Preparation and ion-exchange properties of zirconium tungstoarsenate

A new inorganic ion-exchanger, zirconium tugnstoarsenate, has been synthesized which has been characterized by chemical analysis, thermogravimetry, X-ray and infrared spectroscopy. The ion exchanger has been found to be stable in acids and neutral salt solutions. The Kd values for 30 metal ions have been determined at pH 3–4 which show that the exchanger has high affinity for UO22+, ZrO2+, Cs+ and Tl+ ions. The variation of Kd for a number of metal ions as a function of concentration of nitric acid and ammonium nitrate has been investigated to elucidate the probable exchange mechanism and to work out conditions for elution. Some binary separations, viz. Sr2+−Cs+, Sr2+−Rb+, Sr2+−Y3+, Fe3+−Al3+, Fe3+−Zn2+ and Zn2+−Hg2+ in trace amounts have been carried out on the column of the exchanger which demonstrate the utility of the exchanger in radionalytical and analytical chemistry.

Chromatographic separations on pyridinium tungstoarsenate-impregnated ion-exchange papers

Ion-exchange papers were prepared by impregnating chromatographic Whatman No. 3 paper with pyridinium tungstoarsenate exchanger. The composition of the material loaded on the paper shows that the compound has the formula (C5H5NH)3 W1 2AsO4 0·Rf values of 30 metal ions were determined on these ion-exchange papers by developing with ascending technique in solvents containing mixtures of n-propanol and hydrochloric or nitric acid. Several binary, ternary and some quaternary separations were also achieved on these papers. Studies were also made on plain papers for comparison.