Laser-induced breakdown spectroscopy for simultaneous determination of Sm, Eu and Gd in aqueous solution

This paper reports studies on the determination of trace levels of samarium, europium and gadolinium in aqueous samples by laser-induced breakdown spectroscopy (LIBS). In this work, a membrane-based filter paper was used as a sample support for the liquid samples. The laser-induced plasma was produced in air at atmospheric pressure, using a pulsed Nd:YAG laser. Calibration standards and synthetic mixtures of these lanthanides were prepared using solutions prepared from respective high purity oxides. Linear calibration was obtained for Sm, Eu and Gd by normalizing the intensities of lanthanides emission lines with respective to C(I) 193.029 nm emission line. The concentrations of Sm, Eu and Gd were then determined in a solution containing a mixture of these lanthanides. The concentrations of individual lanthanides were obtained within 5% of the expected values. Limits of detection were found to be 1.3 ppmw (Sm), 1.9 ppmw (Eu) and 2.3 ppmw (Gd).     

Determination of boron at sub-ppm levels in uranium oxide and aluminum by hyphenated system of complex formation reaction and high-performance liquid chromatography (HPLC)

Boron, at sub-ppm levels, in U3O8 powder and aluminum metal, was determined using complex formation and dynamically modified reversed-phase high-performance liquid chromatography (RP-HPLC). Curcumin was used for complexing boron extracted with 2-ethyl-1,3-hexane diol (EHD). Separation of complex from excess reagent and thereafter its determination using the online diode array detector (DAD) was carried out by HPLC. Calibration curve was found to be linear for boron amounts in the sample ranging from 0.02 microg to 0.5 microg. Precision of about 10% was achieved for B determination in samples containing less than 1 ppmw of boron. The values obtained by HPLC were in good agreement with the data available from other analytical techniques. The precision in the data obtained by HPLC was much better compared to that reported by other techniques. The present hyphenated methodology of HPLC and complex formation reaction is interesting because of cost performance, simplicity, versatility and availability when compared to other spectroscopic techniques like ICP-MS and ICP-AES.     

Fe(Cp)2PF6 catalyzed efficient Strecker reactions of ketones and aldehydes under solvent-free conditions

The synthesis of α-aminonitriles of ketones and aldehydes was performed in very short reaction times (20 min) with excellent yields in the presence of 5 mol % of Fe(Cp)₂PF₆ under solvent-free conditions.     

Kinetics and mechanism of <Emphasis Type="Italic">L</Emphasis>-isoleucine oxidation by alkaline diperiodatoargentate(III)

The oxidation of L-isoleucine by alkaline diperiodatoargentate(III) (DPA) at 298 K and a constant ionic strength of 0.80 mol dm⁻³ was studied spectrophotometrically. The stoichiometry is [L-isoleucine]: [DPA] = 1:2. The reaction is first order in [DPA] and has less than unit order in both [L-isoleucine] and [alkali] and retarding effect in The oxidation reaction in alkaline medium has been shown to proceed via a L-isoleucine–DPA complex, which further reacts with one molecule of DPA in a rate determining step followed by other fast steps to give the products. Spot test and IR were used to identify the main products. The reaction constants involved in the different steps of the mechanism are calculated. The activation parameters with respect to the slow step of the mechanism are computed and discussed, and thermodynamic quantities are also determined. The probable active species of oxidant have been identified. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

New method for atomistic modeling of the microstructure of activated carbons using hybrid reverse Monte Carlo simulation

We propose a new hybrid reverse Monte Carlo (HRMC) procedure for atomistic modeling of the microstructure of activated carbons whereby the guessed configuration for the HRMC construction simulation is generated using the characterization results (pore size and pore wall thickness distributions) obtained by the interpretation of argon adsorption at 87 K using our improved version of the slit-pore model, termed the finite wall thickness (FWT) model (Nguyen, T. X.; Bhatia, S. K. Langmuir 2004, 20, 3532) . This procedure overcomes limitations arising from the use of short-range potentials in the conventional HRMC method, which make the latter unsuitable for carbons such as activated carbon fibers that are anisotropic with medium-range ordering induced by their complex pore structure. The newly proposed approach is applied specifically for the atomistic construction of an activated carbon fiber ACF15, provided by Kynol Corporation (Nguyen, T. X.; Bhatia, S. K. Carbon 2005, 43, 775) . It is found that the PSD of the ACF15's constructed microstructure is in good agreement with that determined using argon adsorption at 87 K. Furthermore, we have also found that the use of the Lennard-Jones (LJ) carbon-fluid interaction well depth obtained from scaling the flat graphite surface-fluid interaction well depth taken from Steele (Steele, W. A. Surf. Sci. 1973, 36, 317) provides an excellent prediction of experimental adsorption data including the differential heat of adsorption of simple gases (Ar, N(2), CH(4), CO(2)) over a wide range of temperatures and pressures. This finding is in agreement with the enhancement of the LJ carbon-fluid well depth due to the curvature of the carbon surface, found by the use of ab initio calculations (Klauda, J. B.; Jiang, J.; Sandler, S. I. J. Phys. Chem. B 2004, 108, 9842) .     

Pressure and temperature dependence of the chlorine NQR in caesium and sodium chlorates

The (35)Cl nuclear quadrupole resonance (NQR) frequencies (nu(Q)) in caesium and sodium chlorates were measured as a function of temperature, from 77 to 300 K at different pressures up to 5.1 kbar, and the data were analysed to estimate the volume dependence of the electric field gradient (EFG), torsional frequency and also the contributions to the NQR frequency from static and dynamic effects. The variation of spin-lattice relaxation time with pressure at different temperatures was studied in the case of sodium chlorate and at room temperature in case of caesium chlorate. The pressure dependence of the spin-lattice relaxation time (T(1)) suggests that the relaxation is mainly due to the torsional motions.     

Dimerization of aromatic ureido pyrimidinedione derivatives: observation of an unexpected tautomer in the solid state

Ureido pyrimidinedione derivatives with phenyl, 1-naphthyl and 2-naphthyl substituents form stable dimers via quadruple hydrogen bonding, but the 1-naphthyl derivative presents an unexpected tautomer in the solid state.     

Chemoenzymatic synthesis of prodigiosin analogues--exploring the substrate specificity of PigC

Analogues of prodigiosin, a tripyrrolic pigment produced by Serratia species with potent immunosuppressive and anticancer activities, have been produced by feeding synthetic analogues of the normal precursor MBC to mutants of Serratia sp. ATCC 39006 or to engineered strains of Escherichia coli; in this way it has been shown that the prodigiosin synthesising enzyme, PigC, has a relaxed substrate-specificity.