Development of a Cr(III)-specific potentiometric sensor using Aurin tricarboxylic acid modified silica

A new chelating resin, Aurin tricarboxylic acid modified silica, was synthesized. The resin behaves as a selective chelating ion exchanger for Cr(III) at a pH 3.8-5.5. A polyvinyl chloride-based membrane electrode of the modified silica has been fabricated and explored as sensor for Cr(III) ions. The membrane works well over the concentration range 7.0 × 10⁻⁶ to 1 × 10⁻¹ M of Cr(III) with a Nernstian slope of 19.0 mV per decade of concentration. The response time of the sensor is 10 s and it can be used for a period of 5 months. The performance of the sensor is best in the pH range 3.5-6.5 and it also works well in partially non-aqueous medium. The selectivity coefficient values depicts that the membrane exhibits good selectivity over a number of interfering ions. Moreover, the membrane sensor has been applied to analyse the concentration of chromium in certified steel sample and food materials with greater than 97% accuracy.     

Spectrophotometric determination of zirconium with 2-(1-hydroxy-4,6-dinitro-2-phenylazo)-1,8-dihydroxynaphthalene-3,6-disulphonate (picramine ca) as chromogenic reagent

The title compound has been used as a selective reagent for the micro-determination of zirconium in acidic medium (0.5MHCl) and found to be better than Picramine R. Spectrophotometric studies show the formation of a 2:1 (ligand:Zr) water-soluble complex and the reaction is suitable for photometric determination of 0.4-2.8 ppm of zirconium. The colour takes about 90 min to develop fully and is stable for about 20 hr. The molar absorptivity of the complex is 2.4 x 10(4) and the equilibrium constant is of the order of 10(10). The interference due to a number of ions has been studied.     

Polarographic investigations of some copper chelates of 3-arylazopentane-2,4-diones

The polarographic curves of the copper chelates of twelve substituted 3-arylazopentane-2, 4-diones exhibit single 4e diffusion-controlled irreversible waves between pH 2 and 11. The two azo groups in the compound are equivalent so that only a single 4e wave is obtained; no copper reduction wave is observed. The polarographic behaviour differs from that of p-bisazobenzene. There is a linear correlation between the E$\text{1}\text{2}$ values and the Hammett substituent constants.     

Atomization mechanism and determination of Ag,Be, Cd,Li, Na,Sn and Zn in uranium-plutonium matrices by ETA-AAS

The atomization processes involved in the Electrothermal Atomization-Atomic Absorption Spectrometric (ETA-AAS) determination of Ag, Be, Cd, Li, Na, Sn and Zn in the presence of an uranium-plutonium matrix containing 25% Pu have been investigated. The significant fall in the absorbance signal for Ag, Cd, Na and Zn in an uranium matrix and its restoration in the presence of plutonium is probably correlated with the change in the partial pressure of oxygen released from the matrix at/below the signal appearance temperature (T(app)). In case of Li and Sn, the signal remains unaffected irrespective of the U-Pu matrix which might be due to a high T(app) for these analytes. Regarding Be, the steep suppression of the signal in the presence of the plutonium matrix compared to an uranium matrix can be ascribed to the formation of stable Pu-Be compounds (PuBe(13)). Based on these studies, analytical procedures have been developed for the direct determination of nanogram amounts of these analytes in an U-Pu matrix with an average precision of 9% RSD.     

Allocation of Doctors to Health Centres in Haryana State of India — A Case Study

Medical Administrators are usually confronted with the problem of determining the number of doctors to be posted at different health centres within their jurisdiction. In India the number of doctors allocated to a health centre is normally decided without any proper study of the health needs of the area served by the centre. In certain areas the number of doctors posted is considerably different from the requirement of the area. Also, in certain health centres situated in villages lacking in modern amenities, absenteeism among doctors poses a very serious problem in day to day running of the health centres. The problem of allocation is formulated and a heuristic method is suggested for determining the optimum number of doctors to be posted at each health centre in order to maximise the number of patients seen by the doctor per day. The heuristic method is applied to nine health centres of Haryana state of India in order to demonstrate the potential benefits.     

Nickel(II)-selective sensor based on dibenzo-18-crown-6 in PVC matrix

Nickel(II)-selective sensors have been fabricated from poly(vinyl chloride) (PVC) matrix membranes containing neutral carrier dibenzo-18-crown-6 as electroactive material, sodium tetraphenylborate (NaTPB) as an anion excluder and tris-(2-ethylhexyl) phosphate (TEHP) as plasticizing solvent mediator. The membrane having the composition of crown ether:NaTPB:TEHP:PVC in the ratio 10:1:200:200 (w/w) exhibits best results with linear potential response in the concentration range of 1.0 × 10⁻⁵ to 1.0 × 10⁻¹ M and a Nernstian slope of 29.5 mV/decade of activity between 2.6 and 6.8. The sensor exhibits a fast response time of <25 s, is inert towards non-aqueous medium up to 15% (v/v) and was used over a period of 4 months with good reproducibility. It is selective over a number of mono-, bi- and trivalent cations. The practical utility of the sensor has been demonstrated by using it as an indicator electrode in the potentiometric titration of Ni²⁺ against EDTA and also for the estimation of Ni²⁺ in some Indian brand chocolates.     

A copper-selective electrode based on bis(acetylacetone)propylenediimine

The potentiometric response characteristics of Cu²⁺-selective electrodes based on bis(acetylacetone)propylenediimine (I) combined with anion localizing agent (sodium tetraphenyl borate (NaTPB)) and solvent mediators (dibutyl butyl phosphonate (DBBP), tri-n-butyl phosphate (TBP) and chloronaphthalene (CN)) were investigated. The best results for Cu²⁺ sensing was obtained for the electrode membrane containing PVC, I, DBBP and NaTPB in composition 5:100:200:6 (I:PVC:DBBP:NaTPB) (w/w; mg), where the electrode had a Nernstian response (30.0 mV/decade) to Cu²⁺ within the concentration range 1.0 × 10⁻⁵ to 1.0 × 10⁻¹ M and detection limit of 0.5 ppm. The operational pH range of the electrode was 3.3-7.0. Selectivity characteristic of the proposed electrode was also assessed by calculating using fixed interference method matched potential method. The sensor has been successfully used in the potentiometric titration of copper ions with EDTA.     

Oxozirconium(IV) alkoxides

Oxozirconium(IV) alkoxides of the type ZrO(OR)₂·ROH and ZrOCl(OR)·2 ROH, where R is methyl, ethyl, and isopropyl, and ZrO(OCMe ₃)₂·0.5Me ₃COH and ZrOCl(OCMe ₃)·1.5Me ₃COH have been prepared by the reaction of dichloroxozirconium(IV)-2-acetic acid with corresponding alcohols in the presence of appropriate amounts of piperidine. The alkoxides have been isolated and characterised through infrared, thermal and conductance studies.     

Studies on the electrocapillary curves of anionic surfactants in presence of non-ionic surfactants

Polyoxyethylated non-ionic surfactants such as Tween 20, Tween 40, Nonidet P40 and Nonex 501 have been supposed to be associated with cationic characteristics. Studies on the effect of these surfactants on the electrocapillary curves of the anionic surfactants Aerosol IB, Manaxol OT and sodium lauryl sulphate (SLS), show that the electrocapillary maxima shift towards positive potentials. The order of adsorption of the anionic surfactants is SLS > Manaxol OT > Aerosol IB while the shift in maxima is in the order Aerosol IB ~ Manaxol OT > SLS which confirms association of cationic characteristics with the micelles of these non-ionic surfactants. The magnitude of the shift in electrocapillary maxima is Nonex 501 > Nonidet P40 > Tween 20 > Tween 40 which may be the order of magnitude of the positive charge carried by these non-ionic surfactants.