The tube-in-tube technique in electrothermal atomic absorption spectrometry

Summary A new tube-in-tube is presented. It consists of a small graphite tube which is inserted into a usual Perkin-Elmer graphite oven. Three bars, 1×1 mm over the whole length of the tube, prevent direct contact with the outer one and smoothe the temperature profile within the tube. It causes a thermal delay in the atomization of the atomic cloud. Thus, expulsion of the atomic cloud by the thermally expanding inert gas grows less important compared to its growth. A significant increase of sensitivity is the result.

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Die Rohr-in-Rohr-Technik bei der elektrothermalen Atomabsorptions-SpektrometrieII. Das Dreisteg-Rohr

Zusammenfassung Ein neuer Rohr-in-Rohr-Atomisator wird vorgestellt. Er besteht aus einem kleinen Graphitrohr, welches in ein übliches Perkin-Elmer-Graphitrohr hineingebracht wird. Drei Stege (1×1 mm) über die gesamte Rohrlänge verhindern den direkten Kontakt mit dem Außenrohr und glätten das Temperaturprofil im Innenrohr. Die Atomisierung erfolgt thermisch verzögert. Deshalb verliert das Austreiben der Atomwolke durch das sich thermisch ausdehnende Intergas im Verhältnis zu deren Anwachsen an Bedeutung. Ein deutlicher Anstieg der Meßempfindlichkeit ist das Ergebnis.

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Herrn Prof. Dr. W. Fresenius zum 70. Geburtstag gewidmet

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Part I: Atomspektrometrische Spurenanalytik, Bd. 2 (B. Welz, Ed.). Verlag Chemie Weinheim — in print     

Numerical analysis of large elastic-plastic deformation of beams due to dynamic loading

Numerical calculations were performed for two examples of the response of elastic-plastic beams subjected to dynamic loads. These were a simply supported, axially restrained beam under suddenly applied uniform pressure, and an axially restrained, clamped beam with a central mass that is impacted by a projectile. Large elastic-plastic deflections were considered, and the method of finite differences was used. Two different constitutive equations were assumed: the elástic-perfectly plastic relation, and a special elastic-viscoplastic, strain hardening model. Analysis of the results included examining the interaction between the bending moment and the axial force, the variation of the axial force, bending moment and deflection with time, and the propagation velocities of the various phenomena during motion. Experiments were carried out in which a rifle projectile hit a central mass which had been fastened to a clamped beam. Comparison between the theoretical and experimental dynamic deflections shows good agreement for relatively short response times.     

On the structure and conformation of polymer chains in latex particles. I. Small-angle neutron scattering characterization of polystyrene latexes of small diameter

Polystyrene latexes with 40-60 nm diameter and molecular weights ranging from 6 × 10⁴ to 6 × 10⁶ g/mol were synthesized by a two-step equilibrium swelling method, with deuterated polymer forming either the first or second step. Below about 1 × 10⁶ g/mol, small-angle neutron scattering gave zero-angle scattering intensities much higher than expected on the basis of gel permeation chromatography molecular weights. Several models were examined, the leading model based on a core-shell latex structure. The development of such structure was found to depend on the ratio of the radius of gyration of the polymer chain to that of the diameter of the latex particle, reaching a maximum in the range where the polymer chain dimensions are about half that of the latex particle. For the highest molecular weights, normal scattering intensities were found. These results lead to the finding that the polymer chains were compressed in the latex particles with constraining in the range of one to four, for this molecular weight range.     

Sulfated glycopolymer thin films - preparation, characterization, and biological activity

The impact of heparinoid characteristics on model surfaces obtained from immobilization of sole sulfate groups as well as sulfated glycosides, sulfated cellulose, and definite heparin has been investigated. The obtained layers were physico-chemically characterized regarding film thickness, chemical composition, wettability, and surface morphology. Antithrombin adsorption, studied by fluorescence labeling, revealed a strong dependence on the presence of glycosidic structures and on the molecular weight of the grafted saccharide. On contact with whole blood, the coatings resulted in a diminished plasmatic and cellular coagulation in vitro, which did not reflect well the antithrombin binding. Therefore, more complex activating pathways are discussed.     

Crystal polymorphism of protein GB1 examined by solid-state NMR spectroscopy and X-ray diffraction

The study of micro- or nanocrystalline proteins by magic-angle spinning (MAS) solid-state NMR (SSNMR) gives atomic-resolution insight into structure in cases when single crystals cannot be obtained for diffraction studies. Subtle differences in the local chemical environment around the protein, including the characteristics of the cosolvent and the buffer, determine whether a protein will form single crystals. The impact of these small changes in formulation is also evident in the SSNMR spectra; however, the changes lead only to correspondingly subtle changes in the spectra. Here, we demonstrate that several formulations of GB1 microcrystals yield very high quality SSNMR spectra, although only a subset of conditions enable growth of single crystals. We have characterized these polymorphs by X-ray powder diffraction and assigned the SSNMR spectra. Assignments of the 13C and 15N SSNMR chemical shifts confirm that the backbone structure is conserved, indicative of a common protein fold, but side chain chemical shifts are changed on the surface of the protein, in a manner dependent upon crystal packing and electrostatic interactions with salt in the mother liquor. Our results demonstrate the ability of SSNMR to reveal minor structural differences among crystal polymorphs. This ability has potential practical utility for studying the formulation chemistry of industrial and therapeutic proteins, as well as for deriving fundamental insights into the phenomenon of single-crystal growth.     

Domain structure and interphase dimensions in poly(urethaneurea) elastomers using DSC and SAXS

Small‐angle X‐ray scattering (SAXS) and differential scattering calorimetry (DSC) were used to demonstrate distinct differences in domain size, phase separation, and hydrogen bonding in a series of segmented urethaneurea elastomers prepared from isocyanate‐terminated prepolymers and aromatic diamine chain extenders. Two types of prepolymers were studied. The first contained a broadly polydisperse high molecular mass oligomer with relatively high levels of free isocyanate monomer. The second type of prepolymer contained low levels of high molecular mass oligomers with mass fractions greater than 90% of the two‐to‐one adduct of toluene diisocyanate (TDI) to polytetramethylene glycol (PTMEG). The mass fraction of the residual unreacted diisocyanate was less than 0.1% in the second type. Two chain extenders, 4,4′‐methylene bis‐(2‐chloroaniline)(Mboca) and 4,4′‐methylene bis‐(3‐chloro‐2,6‐diethylaniline) (MCDEA), were used to convert the prepolymers to poly(urethaneurea) elastomers. Materials prepared from the prepolymers with low oligomer polydispersity exhibited smaller hard segment domains with more ordered morphology, greater phase separation, and more hydrogen bonding than those prepared from prepolymers with high oligomer polydispersity. These tendencies were enhanced in those elastomers prepared by chain extension with MCDEA compared to those made with Mboca. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2586–2600, 1999     

Pressure–Volume–Temperature properties of polyolefin liquids and their melt miscibility

The pressure–volume–temperature (P–V–T) properties of a number of metallocene-produced polyolefins were measured experimentally at 10 MPa ≤ P ≤ 200 MPa and 30°C ≤ T ≤ 220°C in a dilatometer-type P–V–T apparatus. These included ethylene copolymers typical of linear low density polyethylene, with several α-olefins as comonomers and a wide range of comonomer content. The experimental P–V–T data were correlated with the equations of state from the Sanchez–Lacombe and Flory–Orwoll–Vrij theories. The solubility parameter map of the polyolefins, at atmospheric pressure, was established on the basis of the thermodynamic data. As the temperature increases, the solubility parameter of the polyolefin decreases. The solubility parameters of copolymers of ethylene with propylene, butene, hexene, and octene under constant temperature are all more or less the same at equal weight percent of comonomer. As the incorporation of branches increases, the solubility parameter decreases. The melt miscibility of the polyolefin blends can be predicted to design various blend products for specific applications from this solubility parameter map. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2835–2844, 1999