Subramaniam Muralidharan

DETERMINATION OF THE EQUILIBRIUM CONSTANTS OF ORGANOPHOSPHORUS LIQUID-LIQUID EXTRACTANTS BY INDUCTIVELY COUPLED PLASMA-ATOMIC EMISSION SPECTROSCOPY

ABSTRACT The technique of inductively coupled Plasma-Atomic Emission Spectroscopy(ICP) has been used for determining the equilibrium constants of organophosphorus extractants in liquid-liquid extraction systems. The 213.618am first order atomic emission line of phosphorus was monitored to determine the equilibrium constants. The relevant equilibrium constants of bis(2,4,4-trimethylpentyl)phosphinic acid, bis(2- ethylhexyl)phosphoric acid, diphenylphosphinic acid, trioctylphosphine oxide and tri-n-butylphosphate have been determined in this manner. It has been demonstrated for the first time that the equilibrium constants for liquid-liquid extractants can be determined in a facile manner using ICP.

Improved separation of closely related metal ions by centrifugal partition chromatography

Abstract Centrifugal Partition Chromatography (CPC) has been used for the analytical scale separations of adjacent trivalent lanthanides. The stationary phase was 0.1 M Cyanex 272 (bis(2,4,4-trimethylpentyl)phosphinic acid) in heptane and the mobile phase was water at the appropriate pH. Baseline separations of the adjacent lanthanides were achieved with an observed column efficiency of 320 /pm 40 theoretical plates. The column efficiency decreased with flow rate, i.e., the normal Van Deemter behavior was observed. The distribution ratios (D) of selected trivalent lanthanides at different pH values were in general in good agreement with the values determined by batch solvent extraction method. The D obtained with CPC differed markedly from the solvent extraction values inn certain cases resulting in a dependence of separation factor (α) of adjacent lanthanides on pH. This anomaly is under further investigation. The number of theoretical plates, selectivity and resolution of adjacent lanthanides obtained w...

SELECTIVE EXTRACTION OF TRIVALENT ACTINIDES FROM LANTHANIDES WITH DITHIOPHOSPHINIC ACIDS AND TRIBUTYLPHOSPHATE

A variety of chemical systems have been developed to separate trivalent actinides from lanthanides based on the slightly stronger complexation of the trivalent actinides with ligands that contain soft donor atoms. The greater stability of the actinide complexes in these systems has often been attributed to a slightly greater covalent bonding component for the actinide ions relative to the lanthanide ions. We have investigated several synergistic extraction systems that use ligands with a combination of oxygen and sulfur donor atoms to achieve a good group separation of the trivalent actinides and lanthanides. For example, the combination of dicyclohexyldithiophosphinic acid and tributylphosphate has shown separation factors of up to 800 for americium over europium in a single extraction stage. Such systems could find application in advanced partitioning schemes for spent nuclear fuel and nuclear waste.

SEPARATION OF PALLADIUM(II) FROM PLATINUM(II), IRIDIUM(III), AND RHODIUM(III) USING CENTRIFUGAL PARTITION CHROMATOGRAPHY

ABSTRACT The separation of Pd(II) from Pt(II), Ir(III) and Rh(III) with trioctylphosphine oxide (TOPO) in heptane using centrifugal partition chromatography (CPC) has been investigated for the first time. The extraction of Pd(II) has been studied by CPC and batch solvent extraction. The distribution ratios for Pd(II) determined by both methods agree well. In low HCl concentrations (<0.1 M), the extracted species was PdCl2.(TOPO)2, irrespective of the chloride concentration, while at acid concentrations above 0.1 M, the Pd was extracted as the ion pair, 2(TOPO.H+).PdCl4 2-. Base line separation of Pd(II) and Pt(II) in CPC was obtained under a variety of chloride and HCl concentration with the average number of theoretical plates being 390 ± 40 at a flow rate of 0.47 ± 0.05 mL/min.

Characterization of Micro-Babington and Cross-Flow Type Nebulizers for Inductively Coupled Plasma Atomic Emission Spectrometry

The use of Inductively Coupled Plasma Atomic Emission Spectrometry (ICP/AES) for the analysis of samples which contain either low or high amounts of dissolved solids and/or suspended particles has become common in recent years because of the high sensitivities and multielement capability of this technique. One of the major concerns associated with ICP/AES is the reproducible introduction of the sample aerosol into the plasma. This parameter is commonly thought of as the limiting factor in the reproducibility of experimental results. Although traditional pneumatic nebulizers, such as crossflow or concentric types, can be used for samples containing low amounts of dissolved solids, such nebulizers cannot be used for samples which contain suspended particles and/or high amounts of dissolved solids, because of the possible clogging of the sample capillary. For such samples, either frit, ultrasonic, or Babington-type nebulizers are commonly employed.

Kinetic behavior of lanthanide extraction with acidic phosphorus extractants

The kinetic behavior of lanthanide extraction from HAc-NaAc-EDTA media with three acidic phosphorus extractants(HL), bis(2-ethylhexyl)phosphoric acid (HDEHP), 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH(EHP)) and bis(2,2,4-trimethylpentyl)phosphinic acid (H(DTMPP)) in n-octane solution is reported. The observed rate constants, k o for the metals (M) lanthanum, neodymium, gadolinium, holmium and lutetium with these three extractants were determined under vigorous mixing. The rate equation for extraction was determined to be : 1 formula chem. 2 formula chem. A mechanism has been proposed for the extraction reaction under the experimental conditions. For a given metal the rate constant as a function of ligand followed the order HDEHP > HEH(EHP) > H(DTMPP), the decrease from HDEHP to H(DTMPP) being less than an order of magnitude. It was also found that the rate constants for these metals and yttrium bear an inverse relationship to the stability constants of their complexes with EDTA.

Factors Influencing the Efficiencies of Multistage Separations of Lanthanides

Centrifugal partition chromatography (CPC) a multistage liquid-liquid countercurrent distribution technique has been demonstrated to be valuable for the complete separation of adjacent tervalent lanthanide metal ions. Using bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272) and 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (HPMBP) as the extractants in the heptane-H2O and toluene-H2O phase pairs respectively, the base line separations of light and heavy lanthanides at 25 °C were achieved. It was also shown that a mixture of light and heavy lanthanides could be separated in a single run by the use of a pH gradient in the aqueous mobile phase. These separation studies clearly indicated that the main factor limiting the CPC separation efficiencies was the slow kinetics of back-extraction of the lanthanide complexes. The mechanism of the complex dissociation reactions could be discerned from the dependency of the width of the CPC bands on the extractant concentration and pH. These mechanism were independently verified by stopped-flow kinetic studies in micelles formed by the neutral surfactant Triton X-100. Further a linear correlation was found between CETP (channel equivalent of a theoretical plate) determined from the CPC band widths and the half-lives of the dissociation reactions determined by stopped-flow. The importance of CPC not only as a tool for the separation of tervalent lanthanides but also for gaining fundamental understanding of their complex formation and dissociation kinetics was established in this study.

A Short and Convenient Synthesis of 5-Alkyl Substituted 8-Hydroxyquinolines

Abstract 5-Chloro-8-methoxyquinoline undergoes rapid and reversible lithium-halogen exchange reaction with alkyllithiums to yield 5-alkyl substituted derivatives indirectly, whereas the reaction with phenyllithium is slower and 5-alkyl substituted compounds are formed by the direct addition of alkyl halides.