T. Prasada Rao

Preconcentration techniques for uranium(VI) and thorium(IV) prior to analytical determination- : an overview

The need for the preconcentration of trace and ultratrace amounts of uranium(VI) and thorium(IV) in conjunction with various detection techniques was clearly brought out in the introductory part. Subsequently, various off-line and on-line procedures developed for uranium(VI) and thorium(IV) prior to their analytical determination since 1990 were critically reviewed in terms of enrichment factor, retention/sorption capacity, validation using certified reference materials and application to complex real samples. The relative merits and demerits of various preconcentration and/or separation of uranium(VI) and thorium(IV) prior to quantitation by a plethora of analytical techniques are discussed in concluding part of the review article.

Amberlite XAD-4 functionalized with succinic acid for the solid phase extractive preconcentration and separation of uranium(VI)

Amberlite XAD-4 resin has been functionalized with succinic acid by coupling it with dibromosuccinic acid after acetylation. The resulting resin has been characterized by FT-IR, elemental analysis and TGA and has been used for preconcentrative separation of uranium(VI) from host of other inorganic species prior to its determination by spectrophotometry. The optimum pH value for quantitative sorption of uranium(VI) in both batch and column modes is 4.5-8.0 and desorption can be achieved by using 5.0ml of 1.0moll(-1) HCl. The sorption capacity of functionalized resin is 12.3mgg(-1). Calibration graphs were rectilinear over the uranium(VI) concentrations in the range 5-200mugl(-1). Five replicate determinations of 50mug of uranium(VI) present in 1000ml of solution gave a mean absorbance of 0.10 with a relative standard deviation of 2.56%. The detection limit corresponding to three times the standard deviation of the blank was found to be 2mugl(-1). Various cationic and anionic species at 200-fold amounts do not interfere during the preconcentration of 5.0mug of uranium(VI) present in 1000ml (batch) or 100ml (column) of sample solution. Further, adsorption kinetic and isotherm studies were also carried out by a batch method to understand the nature of sorption of uranium(VI) with the succinic acid functionalized resin. The accuracy of the developed solid phase extractive preconcentration method in conjunction with Arsenazo III procedure was tested by analyzing marine sediment (MESS-3) and soil (IAEA soil-7) reference material. Further, the above procedure has been successfully employed for the analysis of soil and sediment samples.

Solid phase extractive preconcentration of uranium(VI) onto diarylazobisphenol modified activated carbon

Diarylazobisphenol (DAB) 1 and diarylazobisphenol modified carbon 2 were synthesized and characterised. The latter has been used for solid phase extractive preconcentration and separation of trace amounts of uranium(VI) from other inorganics. In this, a column mode preconcentration of uranium(VI) was carried out in the pH range 4.0-5.0, eluted with 1.0moll(-1) HCl and determined by an Arsenazo III spectrophotometric procedure. Calibration graphs were rectilinear over the uranium(VI) concentrations in the range 5-200mugl(-1). Five replicate determinations of 25mug of uranium(VI) present in 1l solution gave a mean absorbance of 0.032 with a relative standard deviation of 2.52%. The detection limit corresponding to three times the standard deviation of the blank was found to be 5mugl(-1). The accuracy of the developed preconcentration method in conjunction with the Arsenazo III procedure was tested by analysing MESS-3, a marine sediment certified reference material. Further, the above procedure has been successfully employed for analysis of uranium(VI) in soil and sediment samples.

Preconcentrative separation of chromium(VI) species from chromium(III) by coprecipitation of its ethyl xanthate complex onto naphthalene

A rapid, sensitive and selective method is described for the determination of chromium(VI) in presence of 100-fold amounts of chromium(III) by flame atomic absorption spectrometry (FAAS) in conjunction with coprecipitative preconcentration of its ethyl xanthate complex onto naphthalene. The solid mixture consisting of the chromium(VI) complex together with naphthalene is dissolved in 8.0ml of dimethyl formamide (DMF) and chromium(VI) content was established by FAAS. Calibration graphs were rectilinear over the chromium(VI) concentration in the range 0-200mugl(-1). Five replicate determinations of 20mug of chromium(VI) present in 1.0l of sample solution gave a relative standard deviation of 3.1%. The detection limit corresponding to three times the standard deviation of the blank was found to be 0.5mugl(-1). The developed procedure has been successfully utilized for the estimation of chromium(VI), chromium(total) (after oxidation with bromate) and chromium(III) (by subtracting chromium(VI) content from chromium(total) value contents of several tannery industries.

Solid phase extraction vis-à-vis coprecipitation preconcentration of cadmium and lead from soils onto 5,7-dibromoquinoline-8-ol embedded benzophenone and determination by FAAS

This article compares the solid phase extraction (SPE) and coprecipitative preconcentration of cadmium and lead from dilute aqueous solutions as a function of pH and weight of chelating agent. SPE enriches cadmium and lead over a wider pH range (6.0-8.0) and requires lower weight of DBQ chelate embedded benzophenone. Among the quinoline-8-ol and its dihaloderivatives, DBQ embedded benzophenone allows quantitative enrichment over a wide pH range (6.0-8.0) for both cadmium and lead unlike DCQ ( approximately 6.5 for Cd and 6.5-7.0 for Pb), DBQ was preferred. The calibration plots were rectilinear over the concentration range of 0.1-50 and 2.5-200mugl(-1) of cadmium and lead with detection limits of 0.1 and 2.0mugl(-1), respectively, which are 400 times lower than the direct FAAS method. The precision of the developed procedure is good as it provides relative standard deviation values of 2.20 and 2.45% during five replicate determinations of 2 and 25mugl(-1) of cadmium and lead, respectively. The accuracy of the developed procedure was tested by analyzing certified reference materials (CRMs) of soil and marine sediment samples supplied by IAEA, Italy and NRC, Canada, respectively. Furthermore, the developed procedure has been successfully used for the speciative determination of cadmium and lead in soil samples collected from the vicinity of industries in India.

Extraction of iron(III) from acidic chloride solutions by Cyanex 923

Abstract The extraction of iron(III) from hydrochloric acid solutions has been investigated using Cyanex 923 (TRPO) in xylene. Extraction increases with increasing concentration of both hydrochloric acid and extractant. The species extracted into the organic phase appears to be HFeCl4 with 2 mol of the solvent. The extraction behaviour of iron(III) was compared with other metal ions: titanium(IV), chromium(VI) and vanadium(V), which are associated with iron in ilmenite leach liquors. The stripping percentage of iron(III) with hydrochloric acid from the loaded Cyanex 923 was found to decrease with an increase in acid concentration. The 100% stripping efficiency of iron(III) can be achieved with 0.4-M hydrochloric acid in two counter-current stages at an aqueous:organic phase ratio of 3:1. The nature of the diluent on the extraction of iron(III) with Cyanex 923 has also been studied and correlated with dielectric constants.

Styrene–Divinyl Benzene Copolymers: Synthesis, Characterization, and Their Role in Inorganic Trace Analysis

Styrene–divinyl benzene copolymers are widely used in inorganic trace analysis for solid-phase extraction preconcentration as well as other fields of application. These include nascent, ionic, and chelate incorporated polymeric materials. Furthermore, the chelate incorporation usually is achieved by surface sorption or by grafting via chemical immobilization and in situ polymerization. This review covers various synthetic approaches adopted by various researchers since 1990. Again, the chemical and morphological characterizations of styrene–divinyl benzene copolymers are also discussed. Finally, a critical account of these polymers in trace analysis of various mono- and multielement analysis of inorganics is brought out in a nutshell.

Molecularly imprinted polymer-based potentiometric sensor for degradation product of chemical warfare agents: Part I. Methylphosphonic acid

A biomimetic potentiometric sensor for the specific recognition of methylphosphonic acid (MPA), the degradation product of nerve agents sarin, soman, VX, etc., was designed. This involves the preparation of MPA imprinted polymer particles and removal of the template by soxhlet extraction. Subsequently, the leached MIP particles were dispersed in 2-nitrophenyloctyl ether (plasticizer) and embedded in polyvinyl chloride matrix. The sensor responds to MPA in the concentration range 5x10(-8) to 1x10(-4) and 1x10(-3) to 1x10(-1)M with a detection limit of 5x10(-8)M. The selectivity of the sensor has been tested with respect to chemical analogues such as phosphoric acid, sodium dihydrogen phosphate, organophosphorous pesticide and triazine herbicides. The utility of the sensor was tested for field monitoring of MPA in spiked ground water.

Solid phase extraction preconcentration of cobalt and nickel with 5,7-dichloroquinone-8-ol embedded styrene-ethylene glycol dimethacrylate polymer particles and determination by flame atomic absorption spectrometry (FAAS)

This article explores the synthesis of styrene-divinyl benzene (DVB)/ethylene glycol dimethacrylate (EGDMA) polymers embedded with quinoline-8-ol (Q) or its dihalo derivatives by thermal means in the presence and absence of 4-vinyl pyridine (VP). The above-synthesized polymers were found to enrich cobalt and nickel present in admixtures. Of these, 5,7-dichloroquinoline-8-ol (DCQ) embedded styrene-EGDMA polymer particles enrich cobalt and nickel quantitatively from dilute aqueous solutions within 5 min of preconcentration time. Styrene-EGDMA, DCQ embedded styrene-EGDMA particles obtained by bulk polymerization and cobalt/nickel bonded polymers were characterized by FTIR, thermogravimetric analysis (TGA), elemental analysis and surface area studies. The use of these polymer particles obtained by bulk polymerization for the solid phase extractive preconcentration of cobalt and nickel was investigated in detail and explores the possibility of employing this procedure for the analysis of cobalt and nickel in soil and sediment samples using a simple, low cost and readily available flame atomic absorption spectrometric instrument was explored.

Trace Determination of Lanthanides in Metallurgical, Environmental, and Geological Samples

ABBREVIATIONS: REE, rare earth elements; MAS, molecular absorption spectrometry; AAS, atomic absorption spectrometry; GFAAS, graphite furnace atomic absorption spectrometry; ETAAS, electrothermal AAS; EDXRF, energy-dispersive X-ray fluorescence spectrometry; TRXRF, Total reflectance XRF NAA, Neutron activation analysis; ICP-AES, inductively coupled plasma atomic emission spectrometry; ICPMS; inductively coupled plasma mass spectrometry; HPLC, high-performance liquid chromatography; IC, ion chromatography; SSMS, spark source mass spectrometry; PIXE, particle-induced X-ray emission; FES, flame emission spectrometry; DCPAES, direct current plasma atomic emission spectrometry; SIMS, secondary ion mass spectrometry; IDMS, isotope dilution mass spectrometry; SEM, scanning electron microscopy; EPMA electron probe microanalysis.