L.P. Singh

Macrocycle based membrane sensors for the determination of cobalt(II) ions

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.

Anion recognition through novel C-thiophenecalix[4]resorcinarene: PVC based sensor for chromate ions.

Novel ionophore, C-thiophenecalix[4]resorcinarene (I) has been synthesized and characterized by IR, NMR and C, H, N analysis. Poly(vinyl chloride) (PVC) based membranes of ionophore (I) using dibutylphthalate (DBP), dioctylphthalate (DOP), 1-chloronapthalene (CN), tris(2-ethylhexyl) phosphate (TEHP) and bis(2-ethylhexyl)sebacate (DOS) as plasticizing solvent mediators were prepared and used as CrO(4)(2-) selective sensors. Of the various sensors prepared, the one with membrane composition 2:66:120mg (I: PVC: DBP) exhibited the best performance. This sensor works well over a wide concentration range 5.6 x 10(-6)-1.0 x 10(-1)M (detection limit approximately 0.30ppm) with Nernstian compliance (29.0mV per decade) between pH 6.5-10.0 with a fast response time of approximately 13s. The selectivity coefficient values as determined by fixed interference method (FIM) indicate excellent selectivity for CrO(4)(2-) ions over a large number of anions. The sensor exhibits adequate shelf-life ( approximately 5 months) with good reproducibility (S.D. +/- 0.2mV). The sensor has been used in the potentiometric titration of chromate with Pb(II). Determination of chromium in electroplating waste using the sensor was successfully achieved.

Copper(II)-selective electrodes based on macrocyclic compounds

Poly(vinyl chloride) based membranes of 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene diperchlorate and 3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene diperchlorate with dibutyl phthalate (DBP) and dioctyl phthalate (DOP) as plasticizing solvent mediator show a Nernstian response for Cu2+ ions over a wide concentration range (1 × 10–5–1 × 10–1 mol l–1) between pH 1.9 and 5.2. These electrodes have been found to be chemically inert and of adequate stability, with a response time less than 30 s. The electrodes are selective over a large number of cations, including HgII, and anions such as Cl– and Br– cause no interference. These electrodes work satisfactorily in partially non-aqueous media and have been used as indicator electrodes in potentiometric titrations of Cu2+ with EDTA.

Neutral carrier and organic resin based membranes as sensors for uranyl ions

Uranyl ion selective electrodes have been constructed from poly(vinyl chloride) matrix membranes containing neutral carrier, 2,3,11,12-dicyclohexano-1,4,7,10,13,16-hexaoxacyclooctadecane and organic resin, 2,4-dihydroxypropiophenoneoxime–formaldehyde using dibutyl phthalate and dioctyl phthalate as plasticizing solvent mediators. These electrodes demonstrate linear response to UO2+2 ions in the concentration range 10–5–10–1 mol l–1 with a Nernstian or near Nernstian slope at pH 3. The electrodes are inert towards acids, salt solutions and non-aqueous media for a period of 3 months and exhibit a response time as fast as 30 s. The electrodes with plasticizers have been found to be better compared with electrodes without plasticizers. The electrodes are sufficiently selective over a large number of bivalent and trivalent cations including calcium, iron(III) and copper(II), with selectivity coefficient values of the order of 0.01 for bivalent and 0.001 for trivalent cations. Monovalent ions cause interference at higher concentrations with selectivity coefficient values of the order of 0.1. The electrodes work satisfactorily in a partially non-aqueous medium.

Sol-Gel processing of silica nanoparticles and their applications.

Recently, silica nanoparticles (SNPs) have drawn widespread attention due to their applications in many emerging areas because of their tailorable morphology. During the last decade, remarkable efforts have been made on the investigations for novel processing methodologies to prepare SNPs, resulting in better control of the size, shape, porosity and significant improvements in the physio-chemical properties. A number of techniques available for preparing SNPs namely, flame spray pyrolysis, chemical vapour deposition, micro-emulsion, ball milling, sol-gel etc. have resulted, a number of publications. Among these, preparation by sol-gel has been the focus of research as the synthesis is straightforward, scalable and controllable. Therefore, this review focuses on the recent progress in the field of synthesis of SNPs exhibiting ordered mesoporous structure, their distribution pattern, morphological attributes and applications. The mesoporous silica nanoparticles (MSNPs) with good dispersion, varying morphology, narrow size distribution and homogeneous porous structure have been successfully prepared using organic and inorganic templates. The soft template assisted synthesis using surfactants for obtaining desirable shapes, pores, morphology and mechanisms proposed has been reviewed. Apart from single template, double and mixed surfactants, electrolytes, polymers etc. as templates have also been intensively discussed. The influence of reaction conditions such as temperature, pH, concentration of reagents, drying techniques, solvents, precursor, aging time etc. have also been deliberated. These MSNPs are suitable for a variety of applications viz., in the drug delivery systems, high performance liquid chromatography (HPLC), biosensors, cosmetics as well as construction materials. The applications of these SNPs have also been briefly summarized.

Preparation of Silica Nanoparticles and its Beneficial Role in Cementitious Materials

Spherical silica nanoparticles (n-SiO2) with controllable size have been synthesized using tetraethoxysilane as starting material and ethanol as solvent by sol-gel method. Morphology and size of the particles was controlled through surfactants. Sorbitan monolaurate, sorbitain monopalmitate and sorbitain monostearate produced silica nanoparticles of varying sizes (80-150 nm), indicating the effect of chain length of the surfactant. Increase in chain length of non-ionic surfactant resulted in decreasing particle size of silica nanoparticles. Further, the size of silica particles was also controlled using NH3 as base catalyst. These silica nanoparticles were incorporated into cement paste and their role in accelerating the cementitious reactions was investigated. Addition of silica nanoparticles into cement paste improved the microstructure of the paste and calcium leaching is significantly reduced as n-SiO2 reacts with calcium hydroxide and form additional calcium- silicate-hydrate (C-S-H) gel. It was found that calcium hydroxide content in silica nanoparticles incorporated cement paste reduced ~89% at 1 day and up to ~60% at 28 days of hydration process. Synthesized silica particles and cement paste samples were characterized using scanning electron microscopy (SEM), powder X-ray diffraction (XRD), infrared spectroscopy (IR) and thermogravimetric analysis (TGA).

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

The potentiometric response characteristics of Cu(2+)-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 Cu(2+) 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 (30.0mV/decade) to Cu(2+) within the concentration range 1.0x10(-5) to 1.0x10(-1)M and detection limit of 0.5ppm. The operational pH range of the electrode was 3.3-7.0. Selectivity characteristic of the proposed electrode was also assessed by calculating K(A,B)(Pot) using fixed interference method matched potential method. The sensor has been successfully used in the potentiometric titration of copper ions with EDTA.

Chelating ionophore based membrane sensors for copper(II) ions

Acetylacetone, ethylacetoacetate and salicyldehyde, are reported to form chelates with copper of high stability as compared to other metals. Therefore, PVC based membranes of bis[acetylacetonato] Cu(II) (A), bis[ethylacetoacetate] Cu(II) (B) and bis[salicyldehyde] Cu(II) (C) have been investigated as copper(II) selective sensors. The addition of sodium tetraphenylborate and various plasticizers, viz., DOS, TEHP, DOP, DBP and TBP have been found to substantially improve the performance of the sensors. The membranes of various compositions of the three chelates were investigated and it was found that the best performance was obtained for the membrane of composition A (1%): PVC (33%): TBP (65%): NaTPB (1%). The sensor shows a linear potential response to Cu(II) over wide concentration range 2.0x10(-6) to 1.0x10(-1)M (detection limit approximately 0.1ppm) with Nernstian compliance (29.3mVdecade(-1) of activity) between pH 2.6 and 6.0 with a fast response time of approximately 9s. The potentiometric selectivity coefficient values as determined by match potential method (MPM) indicate excellent selectivity for Cu(2+) ions over interfering cations. The sensor exhibits adequate shelf life ( approximately 3 months) with good reproducibility (S.D. +/-0.2mV). The sensor has been used in the potentiometric titration of Cu(2+) with EDTA. The utility of the sensor has been tested by determining copper in vegetable foliar and multivitamin capsule successfully.

PVC-BASED NEUTRAL CARRIER AND ORGANIC EXCHANGER MEMBRANES AS SENSORS FOR THE DETERMINATION OF BA2+ AND SR2+

Abstract 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.

Novel PVC-based membrane sensors selective for vanadyl ions

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.