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Membranes of 4-tert-butylcalix[6]arene I as an ion active material in poly(vinyl chloride) (PVC) based matrix have been tried for uranyl-selective sensors. The effect of anion excluder, sodium tetraphenylborate (NaTPB) and plasticizers, tris(2-ethylhexyl)phosphate (TEP), tributyl phosphate (TBP), dibutyl phthalate (DBP), 1-chloronaphthalene (CN) and diphenyl ether (DPE) on the performance of the membrane electrodes has also been studied. It was observed that the membrane having the composition I: PVC:NaTPB:TBP in the ratio 7:52:6:35 gave the best results with a wide working concentration range of3.9× 10–5–1.0–× 10–1 M, Nernstian slope of 29.1 mV per decade of activity, fast response time of 10 s and moderate selectivity over a number of mono-, bi- and trivalent cations. The sensor works well in the pH range 2.2–3.2 and can be successfully employed for the estimation ofUO22+in partially nonaqueous medium having upto 20% (v/v) nonaqueous content. The sensor was used for the estimation of uranium as uranyl ions in simulated mixtures where the results are comparable to those obtained from radiochemical methods.

Polyvinyl chloride (PVC) based membranes of dibenzo-24-crown-8(I) and 4-tert-butylcalix[8]arene (II) with and without plasticizers have been fabricated and explored as sensors for Ba 2+ and Sr 2+ , respectively. The membrane incorporating the ingredients in the ratio 8:50:6:36 [I:PVC:NaTPB (sodium tetraphenylborate): CN (1-chloronaphthalene)] works well over the concentration range 1.4×10 −5 –1.0×10 −1 M of Ba 2+ with a Nernstian slope of 30±1 mV per decade of concentration in the pH range 3.5–8.9 while the membranes of calixarene (11) were tried as Sr 2+ selective sensors and it was observed that the membrane incorporating the ingredients in the ratio 9:50:5:36 {II:PVC:NaTPB: TEP [tris-(2-ethylhexyl) phosphoric acid]} showed the best response with a working concentration range of 2.0×10 −5 –1.0×10 −1 M and a near-Nernstian slope of 31.3±1.0 mV per decade of concentration in the pH range 2.4–4.8. Both sensors exhibit a fast response time of 15 s and work well in partially non-aqueous medium having up to 30% (v/v) alcohol content. The selectivity data showed that the electrodes are sufficiently selective over a number of interfering ions including alkaline earth metals. Anions like Cl − , NO − 3 also do not interfere in the functioning of the sensors.

Poly(vinyl chloride) (PVC) based membranes of 5,10,15,20-tetraphenylporphyrinatocobalt, ( I ), incorporating dibutyl phthalate (DBP) in the composition 9:55:36 ( I :PVC:DBP) responds to molybdate (MoO 2− 4 ) over the concentration range 7.6×10 −6 –1.0×10 −1 mol l −1 , pH between 4.9 and 11.3, with a Nernstian slope and a fast response time of 15 s. The membrane shows excellent selectivity towards MoO 2− 4 ions over a number of other anions and exhibits stable response for more than four months. The sensor can be used in non-aqueous medium with no significant change in the value of slope or working concentration range for the estimation of MoO 2− 4 in solutions having upto 25% (v/v) non-aqueous fraction. It was applied for the estimation of molybdenum as molybdate in a sample of molybdenite, a low grade ore.

A zinc complex of the organic ion exchanger, bis(2,4,4-trimethylpentyl) dithiophosphinic acid, has been used as an electroactive material for the preparation of PVC-based Zn 2+ -selective electrodes. The PVC matrix incorporating sodium tetraphenylborate (NaTPB) as the anion excluder and dibutyl(butyl)phosphonate (DBBP) as the solvent mediator along with the above complex in the ratio 7:29:5:59 (Zn–Cyanex-301:DBBP:NaTPB:PVC) exhibited a working concentration range of 2.8×10 −5 –1.0×10 −1 M, with a slope of 30.1 mV per decade of activity and a fast response time of 15 s. The valid pH range for the membrane sensor is 2.1–6.9 and it can also be used in partially non-aqueous medium having upto 10% (v/v) non-aqueous content. The sensor exhibits good selectivity over a number of other cations and has been applied as indicator electrode in the potentiometric titration of Zn 2+ against EDTA for the determination of end point.

A 20% (w./w.) polystyrene-based heterogeneous membrane of inorganic ion-exchanger, cerium(IV) vanadate, has been prepared and used as a bismuth(III) selective electrode. The electrode gives linear potential response in the concentration range 8.0 × 10−5-1.0 × 10−1 mol L−1 with a slope of 19.2 mV per decade of concentration and a fast response time of 50s. The electrode functions well in the pH range 2.0–4.0, in partially nonaqueous media up to 25% (v./v.) alcoholic content and was used over a period of 4 months without any significant drift in potentials. It exhibits selectivity for Bi3+ over a large number of metal ions and can be used as an indicator electrode to determine Bi3+ by potentiometric titration with EDTA.

5,10,15,20-tetraphenylporphyrin (TPP) and 5,10,15,20-tetra(4-methylphenyl) porphyrin (TMPP) have been explored as electroactive materials for preparing poly(vinyl chloride) (PVC) based membrane sensors selective to Ni 2+ . The membrane incorporating TMPP, sodium tetraphenylborate and a solvent mediator (dibutylphthalate) in PVC in the ratio (7 : 35 : 4 : 54) gave the best results, exhibiting Nernstian response in the concentration range 5.6× 10 −6 –1.0×10 −1 mol/l between pH 2.5–7.4 and a fast response time of 20 s. The electrode shows moderate selectivity and has been used for the quantitative determination of Ni 2+ in chocolates and also as an indicator electrode for the end point detection in the potentiometric titration of Ni 2+ against EDTA.

Poly(vinylchloride) (PVC) and polystyrene based uranyl ion-selective electrodes have been constructed using 2-hydroxyacetophenoneoxime-thiourea-trioxane resin as electroactive material. For PVC based membranes dibutylphthalate (DBP) and dioctylphthalate (DOP) were used as plasticizing solvent mediators. These membrane electrodes work in the concentration range of ca. 10−5–10−1 M with a response time as fast as 30 s. The useful working pH range is 2.5–3.5 and the electrodes perform satisfactorily up to 20 % (v./v.) partially nonaqueous content. The electrodes were used over a period of 4 months with good reproducibility (standard deviation = 0.5 mV). Further, the selectivity coefficient values of the order 0.1 for mono- and bivalent ions indicate moderate selectivity for UO ions over the interfering ions.

Membranes of 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene diperchlorate (I) and 3,5,7,7,10,12, 14, 14-octamethyl-1,4,8, 11-tetraazacyclotetradeca-4,11-diene diperchlorate (II) in PVC and polystyrene binders have been investigated as Ni 2+ -selective sensors. The PVC membranes containing macrocycles, di-n-butylphthalate and dioctylphthalate as plasticizing solvent mediators and sodium tetraphenylborate as an anion excluder show near-Nernstian response in the concentration range ≈ 10 5 -10 1 mol l 1 , while polystyrenebased membranes exhibit linearity in the concentration range ≈ 10 6 -10 1 mol l 1 . These membranes have response times as fast as 15 s and can be used over a period of six months. The electrodes work in the pH range 1.7–5.4 and also perform well in alcohol-water mixtures with alcoholic content up to 50%. The selectivity coefficient values reveal that the electrodes respond to Ni 2+ ions selectively over a large number of cations. The membrane has also been used as an indicator electrode for the determination of the end point in the potentiometric titrationof Ni 2+ against oxine.

Poly(vinyl chloride) (PVC) based membranes of macrocycles, 5,7,7,12,14,14-hexamethyl-1,4,8,11- tetraazacyclotetradeca-4,11-diene diperchlorate (I), 3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclo- tetradeca-4,11-diene diperchlorate (II) and 5,10,15,20-tetraphenylporphyrin(III) with sodium tetraphenylborate (STB) as an anion excluder and dibutyl phthalate (DBP), dioctyl phthalate (DOP), dibutyl butylphosphonate (DBBP) and 1-chloronaphthalene (CN) as plasticizing solvent mediators were prepared and investigated as Co 2 + -selective electrodes. The best performance was observed with the membrane having the composition III–PVC–STB–DBP in the ratio 3:8:1:8, which works well over a wide concentration range (8.0 × 10 - 6 –1.0 × 10 - 1 mol l -1 ) with a Nernstian slope of 29.0 mV per decade of activity between pH 2.8 and 7.3. This electrode shows a fast response time of 20 s and was used over a period of 4 months with good reproducibility (s = 0.4 mV). The selectivity coefficient values of the order of 0.01 for mono-, di- and trivalent cations indicate excellent selectivity for Co 2 + over a large number of cations. Anions such as Cl - and SO 4 2 - do not interfere and the electrode also works satisfactorily in a partially non-aqueous medium. The sensor has been used as an indicator electrode in the potentiometric titration of Co 2 + with EDTA.

Poly(vinyl chloride) (PVC)-based membrane of pentathia-15-crown-5 exhibits good potentiometric response for Hg2+ over a wide concentration range (2.51 × 10−5 to 1.00 × 10−1 mol dm−3) with a slope of 32.1 mV per decade of Hg2+ concentration. The response time of the sensor is as fast as 20 s. The electrode has been used for a period of six weeks and exhibits fairly good discriminating ability towards Hg2+ in comparison to alkali, alkaline and some heavy metal ions. The electrode can be used in the pH range from 2.7 to 5.0.

Poly(vinyl chloride) based membranes of di-(2-ethylhexyl)phosphoric acid (DEHPA) and dibutyl(butyl)phosphonate (DBBP) have been prepared and investigated as VO(2+)-selective sensors. The membranes containing DEHPA/DBBP and sodium tetraphenylborate, an anion excluder, show near-Nernstian/Nernstian response in the concentration range approximately 10(-5)-10(-1) M. The sensors exhibit a fast response time and good selectivity for VO(2+) over a number of other cations. Quantitative determination of vanadium in waste V(2)O(5) catalyst has been achieved by these sensors and they have also been used as indicator electrodes for the determination of the end point in the potentiometric titration of VO(2+) against EDTA.