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  • Author or Editor: T. Reddy x
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Abstract  

The liquid-liquid extraction behavior of Hg(II) from aqueous acidic chloride solutions has been investigated by tracer techniques using dialkylsulphides (R2S) namely, dibutylsulphide (DBS) and dioctylsulphide (DOS) as extractants. These extraction data have been analyzed by both graphical and theoretical methods by taking into account complexation of the metal ion in the aqueous phase with inorganic ligands and all plausible complexes extracted into the organic phase. The results clearly indicate that Hg(II) is extracted into xylene as HgCl2 . nDBS/nDOS (where n = 2 and 3). The equilibrium constants of the extracted complexes have been deduced by non-linear regression analysis. The separation possibilities of Hg(II) from other metal ions viz. Ca(II), Mg(II), Ba(II) and Fe((III), which are present in the industrial wastes of the chlor-alkali industry has also been discussed.

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A quantitative densitometric high-performance thin-layer chromatographic method for determination of nebivolol hydrochloride in pharmaceutical preparations has been established and validated. Nebivolol hydrochloride from the formulations was separated and identified on silica gel 60 F 254 HPTLC plates with toluene-ethyl acetate-methanol-formic acid, 8 + 6 + 4 + 1 ( v / v ), as mobile phase. The plates were developed to a distance of 8 cm. Densitometric quantification was performed at λ = 285 nm by reflectance scanning. Well resolved bands were obtained for nebivolol hydrochloride. The method was validated for precision, recovery, robustness, specificity, and ruggedness. The calibration plot for nebivolol hydrochloride standard was linear with r = 0.9991, slope = 3.291, and intercept = 864.50. The limits of detection and quantification were 18.65 and 62.18 ng per band, respectively. The method is selective and specific with potential application in pharmaceutical analysis.

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Abstract  

The extraction equilibria of175Yb from thiocyanate solutions with di-n-pentyl sulfoxide (DPSO), di-n-octyl sulfoxide (DOSO), tri-n-octylphosphine oxide (TOPO) and their mixtures in carbon tetrachloride has been investigated. A relatively small synergistic enhancement has been observed with mixtures of dialkyl sulfoxides (DPSO+DOSO) and also with mixtures of DPSO+TOPO. These extraction data have been analyzed with the aid of a computer by taking into account complexation of the metal in the aqueous phase by inorganic ligands and assuming a set of product species in the organic phase and adjusting their formation constants through an iterative non-linear least-squares procedure to obtain the best fit to the data. The extraction of the metal is inversely and linearly dependent upon the dielectric constant of the solvent and temperature of the system.

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Abstract  

Synergistic solvent extraction of Eu(III) and Tb(III) from thiocyanate solutions with mixtures of 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (EHPNA) and di-2-ethylhexylphosphoric acid (DEHPA) or tributyl phosphate (TBP) or trioctylphosphine oxide (TOPO) or triphenylphosphine oxide (TPhPO) in benzene has been studied. The mechanism of extraction can be explained by a simple chemically based model presented in this paper. The equilibrium constants of the mixed-ligand species of the various neutral donors have been determined by non-linear regression analysis.

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Abstract  

The extraction of Er(III) and Lu(III) from thiocyanate media with 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (EHEHPA) and also with mixtures of EHEHPA and thenoltrifluoroacetone (HTTA) or tri-n-octylphosphine oxide (TOPO) or bis 2-ethylhexyl sulfoxide (B2EHSO) in benzene has been studied systematically. Synergistic effects have been observed with mixtures of EHEHPA+HTTA or TOPO. On the other hand, antagonistic effects have been observed with mixtures of EHEHPA+B2EHSO. These extraction data have been analyzed theoretically with the aid of a computer by taking into account complexation of the metal in the aqueous phase by SCN and plausible complexation in the organic phase. The extraction constants of the various product species have been deduced by non-linear regression analysis. The stability constants for the thiocyanate complexes of the metal ions have also been determined.

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Abstract  

This paper describes a theoretical method for analyzing the behaviour of65Zn during solvent extraction from ammonium thiocyanate solutions with dialkyl sulphoxides. The mechanism of extraction of Zn/II/ from thiocyanate medium by sulphoxides may be represented by the following general equation:

\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$xM_{aq}^{m + } + ySCN_{aq}^ - + zS_{org} \rightleftharpoons [M_x /SCN/_y ]^{mx - y} .zS_{org}$$ \end{document}
where Mm+ is the metal ion and S is the extractant. Expressions for the distribution coefficients were derived taking into account complexation of the metal in the aqueous phase by inorganic ligands and also the dissociation of the extracted ion-pairs in the organic phase. Using these expressions, the values of the extraction constants were determined by a least-squares fit with the experimental extraction data. From these extraction constants, the various species extracted into the organic phase were resolved. The influence of the metal concentration, temperature and the diluent on the extraction of Zn/II/ has been investigated.

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A densitometric high-performance thin-layer chromatographic (HPTLC) method has been established for quantitative determination of sildenafil citrate in herbal medicinal formulations. Chromatography was performed on silica gel 60 F 254 HPTLC plates, prewashed with methanol, with toluene-acetone-methanol, 6 + 2 + 2 ( v/v ) as mobile phase. The plates were developed vertically, to a distance of 8 cm, in a saturated chamber, and densitometric quantitation was performed at λ = 312 nm by reflectance scanning. Recovery from the herbal medicinal powders and tablets was 83.17% and 99.41%, respectively. The standard sildenafil citrate calibration plot was linear ( r =0.9993) over the concentration range 100–600 ng per spot and the quantitative results showed the sildenafil content of the herbal formulations analyzed was in the range 76.4–85.0 mg | (RSD < 3%). This HPTLC technique is complementary to other chromatographic methods and has potential use for routine quality-control analysis.

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Groundnut (Arachis hypogaea L.) is an important cash crop for tropical farmers. It is an annual legume and its seeds contain high amounts of edible oil (43-55%) and protein (25-28%). Even though it is fairly drought-tolerant, production fluctuates considerably as a result of rainfall variability. To develop a water stress response function in groundnut, research has been done to improve the performance under varying degrees of stress at various physiological stages of crop growth. This review summarizes recent information on the drought resistance characteristics of groundnut with a view to developing appropriate genetic enhancement strategies for water-limited environments. It is suggested that there are considerable gains to be made in increasing yield and stabilizing the yield in environments characterized by terminal drought stress and further exploiting drought escape strategy, by shortening crop duration. Many traits conferring dehydration avoidance and dehydration tolerance are available, but integrated traits, expressed at a high level of organization, are likely to be more useful in crop improvement programs. Possible genetic improvement strategies are outlined, ranging from empirical selection for yield in drought environments to a physiological-genetic approach. It is also suggested that in view of recent advances in understanding drought resistance mechanisms, the latter strategy is becoming more feasible. It is concluded that the use of this recently derived knowledge in a systematic manner could lead to significant gains in yield and yield stability in the world's groundnut production. Research is needed to develop transferable technologies to help farmers in arid and semi-arid regions. Increasing soil moisture storage by soil profile management and nutrient management for quick recovery from drought are some of the areas which need to be explored.

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Abstract  

A simple and sensitive spectrophotometric method is developed for the determination of throium in aqueous medium. The metal ion forms yellow coloured complex with 2,4-dihydroxybenzaldehyde isonicotinoyl hydrazone (2,4-DHBINH) in the pH range 2.0–8.0. The complex shows an absorption maximum at 390 nm. The absorbance of the complex is maximum at pH 5.5 Beer's law is obeyed in the range 0.30–7.00 g/ml of thorium(IV). The molar absorptivity and the Sandell's sensitivity of the method are 2.20· 104 l·mol–1·cm–1 and 0.0106 g/cm–2, respectively. The interference of various ions was studied. The composition of the complex is 1:1 {Th(IV) : 2,4-DHBINH}. The first derivative spectrum of the complex shows a zero cross at 391.2 nm and maximum amplitude at 415 nm. Thus a sensitive derivative spectrophotometric method for the determination of Th(IV) is proposed.

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