High performance liquid chromatographic studies on lanthanides, uranium and thorium on amide modified reversed phase supports

The retention behavior of uranium, thorium and lanthanides has been investigated with amide modified reversed phase C₁₈ supports using α-hydroxy isobutyric acid (α-HIBA) as the mobile phase. Four structurally different amide moieties namely, 4-hydroxy-N,N-dihexyl butyramide (4HHBA), 4-hydroxy-N,N-di-2-ethylhexylhexanamide (4HEHHA), bis(N,N,N′,N′-2-ethylhexyl)malonamide (B2EHM) and N-methyl-tris(dihexylcarbamoyl-3-methoxy)pivolamide (MTDCMPA) have been synthesized and studied. Among the various amide coated columns, the supports modified with 4HHBA, B2EHM and MTDCMPA exhibit an interesting retention for uranium and thorium, which is different from 4HEHHA modified support. The retention time for uranium and thorium increases with increasing amide concentration for 4HHBA, B2EHM and MTDCMPA supports, while the same decreases with increasing 4HEHHA content. However, the separation factor for uranium and thorium is greater on a 4HEHHA support, compared to an unmodified C₁₈ column, reflecting the amide's preferential complexation of uranium over thorium.Columns modified with 4HHBA, B2EHM and MTDCMPA exhibit relatively higher retentions for lanthanides. However, MTDCMPA modified support shows a different elution profile for lanthanides compared to 4HHBA, and B2EHM modified columns. Individual separations of heavier lanthanides, i.e., from gadolinium to lutetium also have been achieved using 4HHBA and B2EHM modified supports.The influence of modifier content, mobile phase concentration and its pH on the retention of metal ions has also been studied. Based on these investigations, an efficient high performance liquid chromatographic method (HPLC) has been developed for the rapid separation of uranium from thorium as well as for the individual separation of heavier lanthanides.     

Dioctyl sulfoxide as a stabilizer for scintillation counting

The use of dioctyl sulfoxide (DOSO) as a stabilizer for scintillation counting of uranium(VI), plutonium(IV) and americium(III) has been investigated. It has been observed that the addition of 2% DOSO to the scintillator solution results in a decrease in count rate of Am(III), which is about one third of that obtained with 2% TOPO. Uranium(VI) could be counted with almost the same efficiency with DOSO, TOPO, or as such without any stabilizer. The counting efficiency of plutonium(IV), however, is inferior for DOSO as compared to TOPO.     

4-Oxatricyclo[5.2.1.0(2,6)]decan-10-one and 4-oxatricyclo[5.2.1.0(2,6)]dec-8-en-10-one. Experimental and DFT investigations of the pi-selectivities.

Ab initio MO and experimental pi-selectivities of hydride additions to 4-oxatricyclo[5.2.1.0(2,6)]decan-10-one and 4-oxatricyclo[5.2.1.0(2,6)]dec-8-en-10-one are described. The interactions of sigma(C1-C2) and sigma(C6-C7) with pi(C=O), on one hand, and those of sigma(C1-C9) and sigma(C7-C8) with pi(C=O), on the other hand, support anti-selectivities for both. This is in full accordance with the experiments. The arguments that are based on electrostatic interactions and electron donation from the ring oxygen do not apply.     

Investigation of the complex formation of plutonium(VI) with 2-thenoyltrifluoroacetone by solvent extraction

The co-ordination of plutonyl ions with 2-thenoyltrifluoroacetone (HTTA) has been investigated by distribution studies of²³⁹Pu between benzene and aqueous perchlorate medium at 25°C in order to understand the nature of the extracted species and their stability. The formation constants of the first and second complexes have been evaluated by Rydberg's graphical method as well as by least squares analysis of the distribution data using a computer programme. The overall formation constant (β₂) for Pu(VI)-HTTA system has been found to be of the order of 10¹².     

Sol-gel-derived prussian blue-silicate amperometric glucose biosensor

A new type of inorganic biosensor is introduced. The sensor comprises glucose oxidase enzymes encapsulated in a sol-gel-derived Prussian blue-silicate hybrid network. Glucose is detected by the biocatalytic reduction of oxygen followed by catalytic reduction of hydrogen peroxide by the Prusian blue catalyst. The sol-gel silicate entails a rigid encapsulating matrix, the Prussian blue provides chemical catalysis and charge mediation from the reduction site to the supporting electrode, and the enzyme is responsible for the biocatalysis. The feasibility of a dual optical/electrochemical mode of analysis is also demonstrated.     

Polymerization of styrene with chromium acetylacetonate and triethylaluminum and diethylaluminum bromide

Kinetics of the polymerization of styrene in the presence of benzene at 30°C., with chromium acetylacetonate in combination with triethylaluminum and also in combination with diethylaluminum bromide as catalyst, have been studied. Chromium acetylacetonate forms a homogeneous system with triethylaluminum, and chromium acetylacetonate with diethylaluminum bromide behaves as a heterogeneous system. This homogeneous catalyst system, though reported inactive in the polymerization of α-olefins, has been found effective with styrene. Depending on the homogeneity and heterogeneity of the system, the rate of polymerization is proportional to half order and first order of catalyst concentration. A probable reason for the effect of homogeneity on the order of reaction has been discussed. A study of the effect of diethylzinc as a chain-transfer agent has helped to confirm the mechanism of polymerization.     

Kinetics of growth and catechol production byBacillus stearothermophilus BR321

Applied Biochemistry and Biotechnology - A continuous bioprocess for the specialty chemical catechol has been developed usingBacillus stearothermophilus BR321. Themeta pathway for phenol...     

Selective extraction of U(VI) over Th(IV) from acidic streams using di-bis(2-ethylhexyl) malonamide anchored chloromethylated polymeric matrix

A new chelating polymeric sorbent has been developed using Merrifield chloromethylated resin anchored with di-bis (2-ethylhexyl) malonamide (DB2EHM). The modified resin was characterized by CPMAS NMR spectroscopy, FT-NIR-FIR spectroscopy, CHN elemental analysis and also by thermo gravimetric analysis. The fabricated sorbent showed superior binding affinity for U(VI) over Th(IV) and other diverse ions, even under high acidities. Various physio-chemical parameters, like solution acidity, phase exchange kinetics, metal sorption capacity, electrolyte tolerance studies, etc., influencing the resin’s metal extractive behavior were studied by both static and dynamic method. Batch extraction studies performed over a wide range of solution acidity (0.01-10 M) revealed that selective extraction of U(VI) could be achieved even up to 4 M acidity with distribution ratios (D) in the order of ∼10³. The phase exchange kinetics studies performed for U(VI) and Th(IV) revealed that time duration of <15 min was sufficient for >99.5% extraction. But similar studies when preformed for trivalent lanthanides gave very low D values (<50), with the extraction time extending up to 60 min. The metal sorption studies performed for U(VI) and Th(IV) at 5 M HNO₃ was found to be 62.5 and 38.2 mg g⁻¹,respectively. Extraction efficiency in the presence of inferring electrolyte species and inorganic cations were also examined. Metal ion desorption was effective using 10-15 mL of 1 M (NH₄)₂CO₃ or 0.5 M α-hydroxy isobutyric acid (HIBA). Extraction studies performed on a chromatographic column at 5 M acidity were found to give enrichment factor values of 310 and 250 for U(VI) and Th(IV), respectively. The practical utility of the fabricated chelating sorbent and its efficiency to extract actinides from acidic waste streams was tested using a synthetic nuclear spent fuel solution. The R.S.D. values obtained on triplicate measurements (n = 3) were within 5.2%.     

DAPPA grafted polymer: an efficient solid phase extractant for U(VI), Th(IV) and La(III) from acidic waste streams and environmental samples

A new class of polymeric resin has been synthesized by grafting Merrifield chloromethylated resin with (dimethyl amino-phosphono-methyl)-phosphonic acid (MCM-DAPPA), for the preconcentration of U(VI), Th(IV) and La(III) from both acidic wastes and environmental samples. The various chemical modification steps involved during grafting process are characterized by FT-IR spectroscopy, ³¹P and ¹³C-CPMAS (cross-polarized magic angle spin) NMR spectroscopy and CHNS/O elemental analysis. The water regain capacity data for the grafted polymer are obtained from thermo-gravimetric (TG) analysis. The influence of various physico-chemical parameters during the quantitative extraction of metal ions by the resin phase are studied and optimized by both static and dynamic methods. The significant feature of this grafted polymer is its ability to extract both actinides and lanthanides from high-level acidities as well as from near neutral conditions. The resin shows very high sorption capacity values of 2.02, 0.89 and 0.54 mmol g⁻¹ for U(VI), 1.98, 0.63 and 0.42 mmol g⁻¹ for Th(IV) and 1.22, 0.39 and 0.39 mmol g⁻¹ for La(III) under optimum pH, HNO₃ and HCl concentration, respectively. The grafted polymer shows faster phase exchange kinetics (<5 min is sufficient for 50% extraction) and greater preconcentration ability, with reusability exceeding 20 cycles. During desorption process, all the analyte ions are quantitatively eluted from the resin phase with >99.5% recovery using 1 M (NH₄)₂CO₃, as eluent. The developed grafted resin has been successfully applied in extracting Th(IV) from high matrix monazite sand, U(VI) from sea water and also U(VI) and Th(IV) from simulated nuclear spent fuel mixtures. The analytical data obtained from triplicate measurements are within 3.9% R.S.D. reflecting the reproducibility and reliability of the developed method.