Sanjukta A. Kumar

Direct determination of uranium in seawater by laser fluorimetry

A method for estimation of uranium in seawater by using steady state laser flourimetry is described. Uranium present in seawater, in concentration of approximately 3 ng ml(-1) was estimated without prior separation of matrix. Quenching effect of major ions (Cl(-), Na(+), SO(4)(-), Mg(+), Ca(+), K(+), HCO(3)(-), Br(-)) present in seawater on fluorescence intensity of uranium was studied. The concentration of phosphoric acid required for maximum enhancement of fluorescence intensity was optimized and was found to be 5%. Similarly the volume of concentrated nitric acid required to eliminate the quenching effect of chloride and bromide completely from 5 ml of seawater were optimized and was found to be 3 ml. A simple equation was derived using steady state fluorescence correction method and was used for calculation of uranium concentration in seawater samples. The method has a precesion of 1% (1s, n=3). The values obtained from laser fluorimetry were validated by analyzing the same samples by linear sweep adsorptive stripping voltametry (LSASV) of the uranium-chloranilic acid (2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone) complex. Both the values are well in agreement.

A fluoride ion selective Zr(IV)-poly(acrylamide) magnetic composite

A fluoride ion selective magnetic sorbent has been synthesized by the encapsulation of Fe3O4 nanoparticles in a network of Zr(IV) complexed poly(acrylamide) (Zr–PAM). This magnetic sorbent has been found to be efficient for the selective preconcentration of fluoride ions from natural waters. The Zr–PAM/Fe3O4 composite has been characterized using various physico-chemical techniques i.e. energy dispersive X-ray fluorescence (EDXRF), scanning electron microscopy (SEM), Fourier transform infra-red spectroscopy (FTIR) and a vibrating sample magnetometer (VSM). The Zr–PAM/Fe3O4 composite developed in the present work retains the super paramagnetic properties of Fe3O4 nanoparticles, and the results reveal that the sorption is rapid. The composite has a considerably higher fluoride sorption capacity (124.5 mg g−1) compared to other super-paramagnetic fluoride sorbents reported in the literature. Repeated sorption–regeneration cycles seem to suggest reusability of the sorbent for fluoride removal from natural waters, as well as other aqueous solutions having pH in the range 1–9.

Radiation resistance of Deinococcus radiodurans R1 with respect to growth phase

Deinococcus species exhibit an extraordinary ability to withstand ionizing radiation (IR). Most of the studies on radiation resistance have been carried out with exponential phase cells. The studies on radiation resistance of Deinococcus radiodurans R1 with respect to different phases of growth showed that late stationary phase cells of D. radiodurans R1 were fourfold more sensitive to IR and heat as compared with exponential or early stationary phase cells. The increased sensitivity of D. radiodurans R1 to IR in the late stationary phase was not due to a decrease in the intracellular Mn/Fe ratio or an increase in the level of oxidative protein damage. The resistance to IR was restored when late stationary phase cells were incubated for 15 min in fresh medium before irradiation, indicating that replenishment of exhausted nutrients restored the metabolic capability of the cells to repair DNA damage. These observations suggest that stress tolerance mechanisms in D. radiodurans R1 differ from established paradigms.

Extractive fixed-site polymer sorbent for selective boron removal from natural water.

Water contamination by boron is a widespread environmental problem. The World Health Organization (WHO) recommends maximum boron concentration of 2.4 mg L(-1) for drinking water. The paper presents a simple method for preparation of functionalized sheet sorbent for selective extraction of boron from natural water. The pores of commercially available poly(propylene) membrane were functionalized by room temperature in situ crosslinking of poly(vinylbenzyl chloride) with a cyclic diamine piperazine. The precursor membranes were chemically modified with N-methyl D-glucamine which is selective for boron. Characterization of membrane was carried out using scanning electron microscopy (SEM) and attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) techniques. The functionalized membrane has been characterized in terms of parameters that influence the sorption of boron from aqueous streams like pH, uptake capacity, contact time, effects of competing ions and reusability. The maximum boron sorption capacity determined experimentally was 28 mg g(-1). The studies showed that trace concentrations of boron were quantitatively removed from water at neutral pH. The developed fixed site polymer sorbent exhibited high sorption capacity and fast kinetics as compared to various sorbents reported in literature. It was successfully applied for the removal of boron from ground water and seawater samples in presence of high concentration of interfering ions.

Characterization of As (V), As (III) by selective reduction/adsorption on palladium nanoparticles in environmental water samples

Hydrazine (HZ) and sodium borohydride (BH) are commonly used reagents for the production of palladium nanoparticles (PdNP) in aqueous solution and also for the reduction of arsenic from higher oxidation state to lower oxidation state. A methodology based on the quantitative adsorption of reduced arsenic species on PdNP generated in situ by BH and HZ is described to characterize As (V) and As (III) in environmental water samples. It was observed that PdNP obtained by BH gave quantitative recovery of As (V) and (III) and the PdNP obtained by HZ could account for As (III). The reduced palladium particles are collected and dissolved in minimum amount of nitric acid. The quantification of arsenic was carried out using GFAAS. Optimization of the experimental conditions and instrumental parameters were investigated in detail. The proposed procedure was validated by applying it for the determination of the content of total As in Certified Reference Material BND 301-02 (NPL, India). The detection limit of arsenic in environmental water samples was 0.029 microg L(-1) with an enrichment factor of 50. The relative standard deviation (R.S.D.) for 10 replicate measurements of 5 microg mL(-1) was 4.2%. The proposed method was successfully applied for the determination of sub ppm to ppm levels of arsenic (V), (III) in environmental water samples.

Matrix supported tailored polymer for solid phase extraction of fluoride from variety of aqueous streams

Fluoride related health hazards (fluorosis) are a major environmental problem in many regions of the world. It affects teeth; skeleton and its accumulation over a long period can lead to changes in the DNA structure. It is thus absolutely essential to bring down the fluoride levels to acceptable limits. Here, we present a new inorganic-organic hybrid polymer sorbent having tailored fixed-sites for fluoride sorption. The matrix supported poly (bis[2-(methacryloyloxy)-ethyl]phosphate) was prepared by photo-initiator induced graft-polymerization in fibrous and microporous (sheet) host poly(propylene) substrates. These substrates were conditioned for selective fluoride sorption by forming thorium complex with phosphate groups on bis[2-methacryloyloxy)-ethyl] phosphate (MEP). These tailored sorbents were studied for their selectivity towards fluoride in aqueous media having different chemical conditions. The fibrous sorbent was found to take up fluoride with a faster rate (15 min for ≈76% sorption) than the sheet sorbent. But, the fluoride loading capacity of sheet sorbent (4,320 mg kg(-1)), was higher than fibrous and any other sorbent reported in the literature so far. The sorbent developed in the present work was found to be reusable after desorption of fluoride using NaOH solution. It was tested for solid phase extraction of fluoride from natural water samples.

Functionalized polymer sheet sorbent for selective preconcentration and determination of mercury in natural waters

Mercury is considered as a highly toxic and widespread heavy-metal pollutant. In the present work, two flat-sheet polymer sorbents have been synthesized for the selective preconcentration of mercury from natural waters. These are a silver nanoparticle (AgNP)-embedded poly(acrylamide)-grafted poly(propylene) sheet (Ag-PAM-PP) and a 1,8-octanedithiol-functionalized gold-coated poly(propylene) sheet (HS-octyl-S-Au-PP). The functional groups acrylamide and thiol provide the binding sites for Hg2+ ions; whereas silver nanoparticles reduce Hg2+ to Hg0 and it is held on the sheet by amalgam formation. Various factors that influence the preconcentration of Hg2+ from aqueous solution were investigated. Based on the comparison of the experimental results, it was observed that Ag-PAM-PP had superior performance for uptake of Hg2+ from natural water samples in terms of sorption capacity, sorption kinetics and working pH range. The uptake of Hg2+was found to be pH dependent with a maximum of 95% at pH 7.5. The preconcentration of Hg2+ from a large volume of aqueous solution was used to extend the lower limit of the concentration range that can be quantified by EDXRF and CV-AAS. The sorbed Hg(II) from aqueous samples was quantitatively detected within 1 min using EDXRF. The LOD (3σ) for CV-AAS (RSD = 2%) and EDXRF (RSD = 5%) were 6 and 30 μg L−1, respectively. The method was applied for the determination of Hg2+ in groundwater and seawater samples in the presence of a high concentration of interfering ions.

Characterisation of graphite using boron as a marker element

Graphite has many industrial applications. Two of the most important applications are as electrodes in industries and as moderator in nuclear industry. Determination of the Boron Equivalent of the impurity elements in graphite is the most important parameter for certifying the grade of graphite electrode [1]. The use of a suitable method with low limits of determination of boron is therefore necessary. A method has been standardised in Analytical Chemistry Division, BARC for determining trace amounts of boron in graphite electrodes. It involves controlled dissolution of graphite sample powder and measurement of boron by Inductively Coupled Plasma Mass Spectrometer (ICP-MS) using matrix matched standards. The method detection limit is 1 μg g−1. The method Relative Standard Deviation was 5%. The method was verified by spike recovery experiments. Recoveries were found to be within 100±2% in the concentration range of 1 to 100 μg g−1. The developed method has been adopted for the compositional characterizatio...

Optode sensor for on-site detection and quantification of hydroxide ions in highly concentrated alkali solutions

A colorimetric strip sensor has been developed for selective visual detection and quantification of hydroxide ions in a highly concentrated alkali solutions. The sensor was made by immobilizing the 4,4-bis-[3-(4-nitrophenyl) thiourea]diphenyl ether derivative of thiourea in a Whatman 541 filter paper. Immobilization of the derivative was optimized with respect to its concentration, stability and uniformity in the solid substrate. The sensor strip on reaction with hydroxide ions turns orange in color, and the intensity of the color was found to be proportional to the concentration of hydroxide ions. Developed strip sensor exhibits a wide linear dynamic range of 0.5 M to 8 M and a response time within 5 min. The adequate reproducibility as well as reusability of the strip sensor is suitable for a rapid on-site quantification of hydroxide ions in concentrated alkaline media. Developed strip sensor was successfully applied for the determination of hydroxide concentration in nuclear fuel decladding solutions.