A double-stage tube furnace—acid-trapping protocol for the pre-concentration of mercury from solid samples for isotopic analysis

High-precision mercury (Hg) stable isotopic analysis requires relatively large amounts of Hg (>10 ng). Consequently, the extraction of Hg from natural samples with low Hg concentrations (<1–20 ng/g) by wet chemistry is challenging. Combustion–trapping techniques have been shown to be an appropriate alternative [1]. Here, we detail a modified off-line Hg pre-concentration protocol that is based on combustion and trapping. Hg in solid samples is thermally reduced and volatilized in a pure O₂ stream using a temperature-programmed combustion furnace. A second furnace, kept at 1,000 °C, decomposes combustion products into H₂O, CO₂, SO₂, etc. The O₂ carrier gas, including combustion products and elemental Hg, is then purged into a 40 % (v/v) acid-trapping solution. The method was optimized by assessing the variations of Hg pre-concentration efficiency and Hg isotopic compositions as a function of acid ratio, gas flow rate, and temperature ramp rate for two certified reference materials of bituminous coals. Acid ratios of 2HNO₃/1HCl (v/v), 25 mL/min O₂ flow rate, and a dynamic temperature ramp rate (15 °C/min for 25–150 and 600–900 °C; 2.5 °C/min for 150–600 °C) were found to give optimal results. Hg step-release experiments indicated that significant Hg isotopic fractionation occurred during sample combustion. However, no systematic dependence of Hg isotopic compositions on Hg recovery (81–102 %) was observed. The tested 340 samples including coal, coal-associated rocks, fly ash, bottom ash, peat, and black shale sediments with Hg concentrations varying from <5 ng/g to 10 μg/g showed that most Hg recoveries were within the acceptable range of 80–120 %. This protocol has the advantages of a short sample processing time (～3.5 h) and limited transfer of residual sample matrix into the Hg trapping solution. This in turn limits matrix interferences on the Hg reduction efficiency of the cold vapor generator used for Hg isotopic analysis.     

Pump-limited, 203 W, single-frequency monolithic fiber amplifier based on laser gain competition

We present high power results of a Yb-doped fiber amplifier seeded with a combination of broad and single-frequency laser signals. This two-tone concept was used in conjunction with externally applied or intrinsically formed thermal gradients to demonstrate combined stimulated Brillouin scattering suppression in a copumped monolithic, polarization-maintaining (PM) fiber. Depending on the input parameters and the thermal gradient, the output power of the single-frequency signal ranged from 80 to 203?W with slope efficiencies from 70% to 80%. The 203?W amplifier was pump limited and is, to the best of our knowledge, the highest reported in the literature for monolithic, PM single-frequency fiber amplifiers.     

Rapid determination of isocitrate dehydrogenase mutation status of human gliomas by extraction nanoelectrospray using a miniature mass spectrometer

Analytical and Bioanalytical Chemistry - Isocitrate dehydrogenase (IDH) I and II mutations in gliomas cause an abnormal accumulation of 2-hydroxyglutarate (2-HG) in these tumor cells. These...     

Detection of Bacillus endospores using total luminescence spectroscopy

Detection and analysis of bacteria from environmental samples (e.g. water, air, and food) are usually accomplished by standard culture techniques or by analyses that target specific DNA sequences, antigens or chemicals. For large cell numbers in aqueous suspensions, an alternative technique that has proven useful is total luminescence spectroscopy (TLS). TLS is the acquisition of fluorescence data that records the unique excitation-emission matrix (EEM) of compound fluorophores. Past work has shown that one type of bacterial endospore, Bacillus megaterium, possessed a distinct EEM pattern useful for differentiating it in complex biological fluids and suspensions. The work described here extends those observations to establish some limits on the sensitivity and specificity of TLS for the detection and analysis of bacterial endospores versus (bacterial) vegetative cells in aqueous culture. Our findings show Bacillus endospores exhibit a dramatic blue shift of 130 nm in excitation and a smaller shift of 50 nm in emission when compared to ancillary endospore and non-endospore forming bacterial cells.     

Embracing ligands. Synthesis, characterisation and the correlation between 59Co NMR and ligand field parameters of Co(III) complexes with a new class of nitrogen-thioether multidentate ligand

The syntheses of the hexadentate ligands 2,2,10,10-tetra(methyleneamine)-4,8-dithiaundecane (PrN4S2amp), 2,2,11,11-tetra(methyleneamine)-4,9-dithiadodecane (BuN4S2amp), and 1,2-bis(4,4-methyleneamine)-2-thiapentyl)benzene (XyN4S2amp) are reported and the complexes [Co(RN4S2amp)]3+ (R = Pr, Bu, Xy) characterised by single crystal X-ray study. The low-temperature (11 K) absorption spectra have been measured in Nafion films. From the observed positions of both spin-allowed 1A1g-->1T1g and 1A1g-->1T2g and spin forbidden 1A1g-->3T1g and 1A1g-->3T2g bands, octahedral ligand-field parameters (10Dq, B and C) have been determined. DFT calculations suggest that significant interaction between the d-d and CT excitations occurs for the complexes. The calculations offer an explanation for the observed deviations from linearity of the relationship between 59Co magnetogyric ratio and beta(DeltaE)(-1)(beta= the nephelauxetic ratio; DeltaE the energy of the 1A1g-->1T1g transition) for a series of amine and mixed amine/thioether donor complexes.     

Synthesis,characterisation and X-ray structure of a novel porphyrin array employing Zn–O and O–H…O bonding motifs

The preparation and characterisation of the free-base and zinc metallated derivatives of 5,10,15,20-tetrakis(4-(2-(2-hydroxyethoxy)ethoxy)phenyl)porphyrin 1 is described. The X-ray crystal structure of the Zn(II) adduct 2 dimerises in the solid state via an intermolecular polyether oxygen–Zn(II) interaction (O…Zn = 2.124(4) Å). The porphyrin dimers form discrete layers defined by a distance of 5.10 Å between the porphyrin planes in adjacent layers. A bilayer sheeting arrangement of the porphyrin macrocyclic units is achieved through cooperative hydrogen bonding of the ethoxyethanol arms to form 11-membered macrocycles containing four hydrogen bonds.     

A priori error estimates for interior penalty versions of the local discontinuous Galerkin method applied to transport equations

The local discontinuous Galerkin method has been developed recently by Cockburn and Shu for convection‐dominated convection‐diffusion equations. In this article, we consider versions of this method with interior penalties for the numerical solution of transport equations, and derive a priori error estimates. We consider two interior penalty methods, one that penalizes jumps in the solution across interelement boundaries, and another that also penalizes jumps in the diffusive flux across such boundaries. For the first penalty method, we demonstrate convergence of order k in the L^∞(L²) norm when polynomials of minimal degree k are used, and for the second penalty method, we demonstrate convergence of order k+1/2. Through a parabolic lift argument, we show improved convergence of order k+1/2 (k+1) in the L²(L²) norm for the first penalty method with a penalty parameter of order one (h^?1). © 2001 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 17: 545–564, 2001     

Complexation of lanthanides, actinides and transition metal cations with a 6-(1,2,4-triazin-3-yl)-2,2':6',2'-terpyridine ligand: implications for actinide(III)/lanthanide(III) partitioning

The quadridentate N-heterocyclic ligand 6-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-2,2'?:?6',2'-terpyridine (CyMe(4)-hemi-BTBP) has been synthesized and its interactions with Am(III), U(VI), Ln(III) and some transition metal cations have been evaluated by X-ray crystallographic analysis, Am(III)/Eu(III) solvent extraction experiments, UV absorption spectrophotometry, NMR studies and ESI-MS. Structures of 1:1 complexes with Eu(III), Ce(III) and the linear uranyl (UO(2)(2+)) ion were obtained by X-ray crystallographic analysis, and they showed similar coordination behavior to related BTBP complexes. In methanol, the stability constants of the Ln(III) complexes are slightly lower than those of the analogous quadridentate bis-triazine BTBP ligands, while the stability constant for the Yb(III) complex is higher. (1)H NMR titrations and ESI-MS with lanthanide nitrates showed that the ligand forms only 1:1 complexes with Eu(III), Ce(III) and Yb(III), while both 1:1 and 1:2 complexes were formed with La(III) and Y(III) in acetonitrile. A mixture of isomeric chiral 2:2 helical complexes was formed with Cu(I), with a slight preference (1.4:1) for a single directional isomer. In contrast, a 1:1 complex was observed with the larger Ag(I) ion. The ligand was unable to extract Am(III) or Eu(III) from nitric acid solutions into 1-octanol, except in the presence of a synergist at low acidity. The results show that the presence of two outer 1,2,4-triazine rings is required for the efficient extraction and separation of An(III) from Ln(III) by quadridentate N-donor ligands.     

Mercer’s Theorem on General Domains: On the Interaction between Measures, Kernels, and RKHSs

Given a compact metric space X and a strictly positive Borel measure ν on X, Mercer’s classical theorem states that the spectral decomposition of a positive self-adjoint integral operator T _k :L ₂(ν)→L ₂(ν) of a continuous k yields a series representation of k in terms of the eigenvalues and -functions of T _k . An immediate consequence of this representation is that k is a (reproducing) kernel and that its reproducing kernel Hilbert space can also be described by these eigenvalues and -functions. It is well known that Mercer’s theorem has found important applications in various branches of mathematics, including probability theory and statistics. In particular, for some applications in the latter areas, however, it would be highly convenient to have a form of Mercer’s theorem for more general spaces X and kernels k. Unfortunately, all extensions of Mercer’s theorem in this direction either stick too closely to the original topological structure of X and k, or replace the absolute and uniform convergence by weaker notions of convergence that are not strong enough for many statistical applications. In this work, we fill this gap by establishing several Mercer type series representations for k that, on the one hand, make only very mild assumptions on X and k, and, on the other hand, provide convergence results that are strong enough for interesting applications in, e.g., statistical learning theory. To illustrate the latter, we first use these series representations to describe ranges of fractional powers of T _k in terms of interpolation spaces and investigate under which conditions these interpolation spaces are contained in L _∞(ν). For these two results, we then discuss applications related to the analysis of so-called least squares support vector machines, which are a state-of-the-art learning algorithm. Besides these results, we further use the obtained Mercer representations to show that every self-adjoint nuclear operator L ₂(ν)→L ₂(ν) is an integral operator whose representing function k is the difference of two (reproducing) kernels.