Isotope dilution mass spectrometry for micro- and trace-element determination

Isotope dilution mass spectrometry is an important method for accurate and precise determination of trace- and micro-amounts of the elements. Using different ionization techniques in the mass spectrometer most of the elements of the periodic table can be analysed.     

Ab initio calculation of the two lowest excited states of H2S relevant for the photodissociation in the first continuum

We present extensive MRD CI ab initio calculations for the first two excited states of ¹A″ symmetry (¹B₁ and ¹A₂ in the C_2v point group). Full three-dimensional potential energy surfaces are constructed by varying both H---S-bond lengths as well as the HSH bending angle. The lower adiabatic potential is dissociative whereas the upper one is binding. These surfaces, together with the transition dipole moments with the ground electronic state, form the basis for future investigations of the photodissociation of hydrogen sulfide.     

Ultra-trace analysis of U,Th, Ca and selected heavy metals in high purity refractory metals with isotope dilution mass spectrometry

A method for the determination of trace impurities (U, Th, Ca, Fe, Cr, Ni, Cu, and Cd) in the refractory metals molybdenum and tungsten with isotope dilution mass Spectrometry (IDMS) has been developed. This method enables determinations of uranium and thorium down to the lowest pg/g level with high precision and accuracy. Selective chromatographic, extractive and electrolytic methods for the trace-matrix separation were combined with positive thermal ionization mass spectrometry. Different samples of high purity (4N) and of ultra high purity (UHP) materials for advanced technologies were analysed. The detection limits reached are (in ng/g): U 0.006, Th 0.008, Ca 10, Fe 19, Cr 0.5, Ni 0.6, Cu 2.7, and Cd 0.12. A comparison of results with other sensitive analytical methods (ICP-MS, GDMS, SIMS) makes obvious the urgent necessity of a reliable calibration method like IDMS because the analytical results obtained by the other methods often spread over a wide range.     

A modular approach toward functionalized three-dimensional macromolecules: from synthetic concepts to practical applications

A new strategy for the preparation of functional, multiarm star polymers via nitroxide-mediated "living" radical polymerization has been explored. The generality of this approach to the synthesis of three-dimensional macromolecular architectures allows for the construction of nanoscopically defined materials from a wide range of different homo, block, and random copolymers combining both apolar and polar vinylic repeat units. Functional groups can also be included along the backbone or as peripheral/chain end groups, thereby modulating the reactivity and polarity of defined portions of the stars. This modular approach to the synthesis of three-dimensional macromolecules permits the application of these tailored materials as multifunctional hosts for hydrogen bonding, nanoparticle formation, and as scaffolds for catalytic groups. Examples of applications of the functional stars in catalysis include their use in a Heck-type coupling as well as an enantioselective addition reaction.     

Development of an ICP-IDMS method for accurate routine analyses of toxic heavy metals in polyolefins and comparison with results by TI-IDMS

An inductively coupled plasma isotope dilution mass spectrometric (ICP-IDMS) method was developed as a suitable method - with respect to its sensitivity, precision, accuracy, and time-consumption - for the analysis of toxic heavy metal traces (Pb, Cd, Cr, and Hg) in polyolefins. Results for Pb, Cd, and Cr were compared with those obtained by thermal ionization isotope dilution mass spectrometry (TI-IDMS), which was used as a reference method. Because of its high first ionization potential and its high volatility mercury could not be determined by TI-IDMS. A multi-element spike solution, containing isotopically enriched 206Pb, 116Cd, 53Cr, and 201Hg, was used for the isotope dilution step. Decomposition of the polyolefin samples was carried out with concentrated HNO3 at temperatures of about 300 degrees C in a high pressure asher (HPA). This procedure decomposes polyolefins completely and allows isotopic equilibration between sample and spike isotopes. Detection limits of 16 ng/g, 5 ng/g, 164 ng/g, and 9 ng/g were obtained for Pb, Cd, Cr, and Hg by ICP-IDMS using only sample weights of 0.25 g. In different commercially available polyethylene samples heavy metal concentrations in the range of < 5 ng/g to 4 x 10(3) ng/g were analyzed. Both mass spectrometric methods were applied within the EU project "Polymeric Elemental Reference Material (PERM)" for the certification of two polyethylene reference materials. The ICP-IDMS results agreed very well with those of TI-IDMS which demonstrates the accuracy of the ICP-IDMS method also suitable for routine analyses.     

Efficient Continuous Wave-laser emission of Pr3+-doped fluorides at room temperature

We report, to our knowledge for the first time, Continuous Wave (CW) laser emission at room temperature of Pr:LiYF₄ (Pr.YLF) at six wavelengths: 522, 545, 607, 639.5, 720 and 907.4 nm. The pump source was an argon-ion laser tuned to a wavelength of = 457.9 nm. The maximum output powers at 522 nm (³P_i ³H₅) and 639.5 nm (³P₀ ³F₂) were 144 and 266 mW, respectively. We also observed CW laser action of Pr:GdLiF₄ (Pr: GLF) at = 639 nm and of Pr:KYF₄ (Pr: KYF) at = 642.5 nm.     

Two-dimensional on-line detection of brominated and iodinated volatile organic compounds by ECD and ICP-MS after GC separation

Inductively coupled plasma-mass spectrometry (ICP-MS) was coupled to a gas chromatographic (GC) system with electron capture detector (ECD), which enables relatively easy characterization and quantification of brominated and iodinated (halogenated) volatile organic compounds (HVOCs) in aquatic and air samples. The GC-ECD system is connected in series with an ICP-MS by a directly heated transfer line and an outlet port-hole for elimination of the ECD make-up gas during ignition of the plasma. The hyphenated GC-ECD/ICP-MS system provides high selectivity and sensitivity for monitoring individual HVOCs under fast chromatographic conditions. The ECD is most sensitive for the detection of chlorinated and brominated but the ICP-MS for iodinated compounds. The greatest advantage of the use of an ICP-MS is its element-specific detection, which allows clear identification of compounds in most cases. The absolute detection limits for ICP-MS are 0.5 pg for iodinated, 10 pg for brominated, and 50 pg for chlorinated HVOCs with the additional advantage that calibration is almost independent on different compounds of the same halogen. In contrast to that detection limits for ECD vary for the different halogenated compounds and lie in the range of 0.03-11 pg. The two-dimensional GC-ECD/ICP-MS instrumentation is compared with electron impact mass spectrometry (EI-MS) and microwave induced plasma atomic emission detection (MIP-AED). Even if EI-MS has additional power in identifying unknown peaks by its scan mode, the detection limits are much higher compared with GC-ECD/ICP-MS, whereas the selective ion monitoring mode (SIM) reaches similar detection limits. The MIP-AED detection limits are at the same level as EI-MS in the scan mode.