Kathrin Hametner

An alternative data acquisition and evaluation strategy for improved isotope ratio precision using LA-MC-ICP-MS applied to stable and radiogenic strontium isotopes in carbonates

Strontium isotopes in various marine carbonates were determined using an “AXIOM” MC-ICP-MS in combination with a NewWave UP193 laser ablation unit. Using a modified measurement and data reduction strategy, an external reproducibility of 87Sr/86Sr ratios in carbonates of about 19 ppm (RSD) was achieved. For recent and sub-recent marine carbonates a mean radiogenic strontium isotope ratio 87Sr/86Sr of 0.709170 ± 0.000007 (2SE) was determined, which agrees well with the value of 0.7091741 ± 0.0000024 (2SE) reported for modern sea water (J. M. McArthur, D. Rio, F. Massari, D. Castrodi, T. R. Bailey, M. Thirlwall and S. Houghton, Palaeogeogr. Palaeoclimatol. Palaeoeco., 2006, 242(126), 2006). Compared to published laser-based methods, an improved accuracy and precision was achieved by applying a new data reduction protocol using the simultaneous responses of all isotopes measured. The latter is considered as a new principal approach for isotope ratio evaluation using LA-MC-ICP-MS. A major advantage of the presented method is the direct determination of the stable strontium isotope fractionation. Providing reproducible sample ablation, introduction into the plasma and stable plasma condition, this method excludes the efforts of a quantitative strontium recovery after ion chromatographic separation to avoid additional fractionation of the sample strontium due to chemical pre-treatment/separation (ion chromatography and solution preparation), and is therefore, together with the quicker sample preparation and spatially resolved analysis, advantageous when compared to published solution–nebulization bracketing-standard MC-ICP-MS methods for stable strontium isotope determination.

Magnetic anisotropy of carbonate minerals at room temperature and 77 K

Abstract The relationship between magnetic properties and chemical composition of 19 natural carbonate single crystals of the calcite, aragonite, and dolomite groups and of azurite were investigated. Magnetic susceptibility was determined in low fields, and magnetic anisotropy was measured at room temperature and at 77 K using a high-field torque magnetometer. The chemical composition was analyzed using LA-ICP MS. Planar arrangement of the CO3-groups generates an oblate diamagnetic anisotropy with the minimum susceptibility k3 along the crystallographic c-axis in all investigated anhydrous carbonate minerals. A prolate paramagnetic anisotropy with the maximum susceptibility k1 along the c-axis is produced by Fe2+ in the trigonal carbonate lattice, which can lead to a transition from oblate to prolate shape of the total anisotropy. The transition occurs in the calcite structure above an Fe concentration of 400 ppm at room temperature and 150 ppm at 77 K. The susceptibility difference k1 - k3 for pure calcite is 4.06 × 10-10 m3/kg and increases to 9.4 × 10-9 m3/kg for 10 800 ppm Fe. In the hexagonal aragonite structure, no paramagnetic anisotropy due to Fe2+ was detected. Azurite shows a strong anisotropy with k1 - k3 = 1.5 × 10-8 m3/kg, which is assigned to Cu2+. The paramagnetic anisotropy due to Fe2+ increases at 77 K in minerals of the calcite and dolomite group and in azurite, but not in minerals of the aragonite group. Upon cooling from room temperature to 77 K, k1 - k3 increases 13.3 times for 500 ppm to 100 000 ppm Fe2+ in the trigonal lattice and 7.2 times for siderite.

New spinel oxide catalysts for visible-light-driven water oxidation

Nanoscale Co–Mn–Ga spinels are promoted by the “synergistic” interaction of Co and Mn, thus paving the way to tailored and flexible catalyst design concepts for visible-light-driven water oxidation.

Development and characterization of custom-engineered and compacted nanoparticles as calibration materials for quantification using LA-ICP-MS

The flame spray technique was used to produce a nano-material with a customized composition. Liquid organic precursors of Si, Ca, Ti, Mg, Fe, and Al in a concentration similar to the matrix of the well-known NIST SRM 610 glass standard were mixed with a selection of rare earth elements (Ce, Gd, Ho, and Tb), precious metals (Ag, Au, Pd, Pt, Rh, and Ru) and Pb at concentrations of approx. 400–500 mg kg−1. The liquid precursor mixture was sprayed and collected as nanopowder, compacted to pellets and analyzed by solution and laser-ablation inductively coupled plasma mass spectrometry. The bulk composition of the material was determined in several aliquots of the powder, either 25 mg or 50 mg. Electron microprobe analyses were carried out to further characterize the major element composition of the pressed nano-material. The pellet was ablated using different laser ablation systems with an aim of assessing the micro-scale homogeneity of the produced material. The manufactured material is homogeneous for major elements and REEs similar to the NIST glass (<5% RSD). However, the distribution of the PGEs showed some larger spatial variation in the order of <7.5%. In addition it is shown that contamination during production leads to heterogeneous distribution of Pb and Ag. Based on the results achieved for Ru, Rh, Pd, Au, Pt, Mg, Ti, and Fe, which are either absent or not available in sufficient concentration levels in NIST glass, it is demonstrated that flame spray synthesis allows production of suitable customized matrix-matched calibration materials for micro-analytical techniques.

Manganese distribution in polystyrene beads prepared by copolymerization with cross-linking dendritic salens using laser ablation inductively coupled plasma mass spectrometry

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) with an ArF 193-nm excimer laser was used to determine the Mn content of polystyrene beads (diameter ca. 400 µm) obtained by radical cross-linking suspension copolymerization of chiral, dendritically styryl-substituted salens with styrene and loading with Mn(OAc)2/LiCl to give polymer-bound Mn-Salen complexes (p-1· and p-2 · Mn(Cl)). The beads were used to catalyze the enantioselective epoxidation of styrene to the corresponding epoxide. The spatial distribution of Mn (and Li) in freshly prepared, in multiply used (up to 20 times), or in “reloaded” beads was measured by drilling with laser craters (ablation) of ca. 40 µm into whole beads or into beads cut in half and analyzing the vaporized and ionized material in a plasma (detection limits down to 10 µg/g and depth resolution down to 0.3 µm/pulse). The following results were obtained: (i) the Mn content is evenly distributed within the freshly prepared and loaded beads; (ii) the high-performance polymer (p-2 · Mn(Cl)) leaches Mn down to a constant value of ca. 25% of the original content after 15 sequential uses; (iii) the low-performance polymer (p- 1 · Mn(Cl), a hydroquinone derivative) loses almost all Mn after six runs; (iv) reloading of beads with Mn causes increased Mn content only on the outer layers of the particle; (v) leaching occurs by loss of Mn, increasing from the surface to the center of the beads. It was demonstrated for the first time that LA-ICP-MS is well suited to assessing element distribution inside individual beads containing catalytically active transition metal sites and to detecting spatial change s upon multiple use.  2003 Elsevier Science (USA). All rights reserved.

Analyses of lithium-doped and pure magnesium diboride using ultraviolet nano- and femtosecond laser ablation inductively coupled plasma mass spectrometry

Lithium-doped and pure magnesium diboride crystals were quantified by nanosecond and femtosecond laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). In both cases, non-matrix matched calibration using a silicate glass (NIST SRM 610) was performed. The application of nanosecond LA-ICP-MS resulted in a boron and magnesium stoichiometry of MgB. In contrast, data obtained by femtosecond LA-ICP-MS indicate a boron and magnesium stoichiometry of MgB2, which was supported by supplementary measurements on the basis of X-ray diffraction using peak refinement. Concentration discrepancies of main constituents that suggest a wrong stoichiometry, as found for ns-LA-ICP-MS, have not yet been reported and can, therefore, be considered an example of extreme laser-induced elemental fractionation.