Development of supermolecular structure in polystyrene latexes

The development of supermolecular structure in polystyrene latex particles was investigated by small-angle neutron scattering (SANS). Seed latexes of deuterated polystyrene were swollen with an equal mole-% of protonated styrene monomer, equilibrated, and polymerized to complete conversion. The scattering patterns reflect the extent of supermolecular structure development inside the particle. The data were analyzed by separating the Debye single-chain and spherical scattering form factors. The extent of segregation was found to depend on the relative size of the chains compared with that of the particle, going through a maximum at the ratio M_w/D of about 0.1, where D_w represents the weight-average diameter of the latex particle. When the chain dimensions are relatively very small, uniform molecular mixing is obtained. The best model for the segregated system is a graduated core-shell supermolecular structure.     

On-line species-unspecific isotope dilution analysis in the picomolar range reveals the time- and species-depending mercury uptake in human astrocytes

In order to reveal the time-depending mercury species uptake by human astrocytes, a novel approach for total mercury analysis is presented, which uses an accelerated sample introduction system combined on-line with an inductively coupled plasma mass spectrometer equipped with a collision/reaction cell. Human astrocyte samples were incubated with inorganic mercury (HgCl₂), methylmercury chloride (MeHgCl), and thimerosal. After 1-h incubation with Hg²⁺, cellular concentrations of 3 μM were obtained, whereas for organic species, concentrations of 14–18 μM could be found. After 24 h, a cellular accumulation factor of 0.3 was observed for the cells incubated with Hg²⁺, whereas the organic species both showed values of about 5. Due to the obtained steady-state signals, reliable results with relative standard deviations of well below 5 % and limits of detection in the concentration range of 1 ng L^?1 were obtained using external calibration and species-unspecific isotope dilution analysis approaches. The results were further validated using atomic fluorescence spectrometry.

SPECIFIC PHOTOALKYLATION OF POLY U AND OF POLY A WITH 2-PROPANOL AND THEIR MESSENGER PROPERTIES

Ultraviolet light induced free radical alkylation of poly U or of poly A with 2-propanol leads to the specific formation of 6-(2-hydroxy 2-propyl) 5,6-dihydro-UMP or 8-(2-hydroxy 2-propyl)-AMP residues, respectively. The biochemical significance of the alterations in the modified polynucleotides was studied by testing their messenger activities in a cell free system of E. coli. Both photoalkylated poly U and poly A have reduced functional activity, with no change in functional specificity. This was demonstrated by inhibition of polymerization of phenylalanine and lysine directed by photoalkylated poly U and poly A, respectively, and by lack of misincorporation of other amino acids. The modification of poly U also caused the disappearance of misincorporation of serine that was found with the native polynucleotide.     

Determination of heavy metals in seawater and marine organisms by flameless atomic absorption spectrophotometry

Summary For the determination of cadmium in culture water from toxicological experiments with marine organisms direct flameless atomic absorption spectrophotometry seems to be an appropriate method, because it is less complicated than any combination with an extraction method. Unfortunately, it cannot be applied in the g·l^–1-range without modifications, because matrix effects lead to unacceptable variations in the results. It was found that these difficulties can be overcome by the addition of ammonium peroxodisulphate and sulphuric acid. A routine method basing on this effect has been developed.

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Bestimmung von Schwermetallen im Meerwasser und in marinen Organismen durch flammenlose Atomabsorptions-Spektralphotometrie. VI. Cadmiumbestimmung in Kulturwässern von toxikologischen Experimenten mit Meeresorganismen

Zusammenfassung Zur Cadmiumbestimmung in Kulturwasser von toxikologischen Versuchen mit marinen Organismen scheint die direkte flammenlose Atomabsorptions-Spektralphotometrie besonders geeignet zu sein, denn sie ist weniger umständlich als jede Kombination mit einer Extraktionsmethode. Ohne Modifikationen kann die Direktbestimmung jedoch im g/l-Bereich nicht eingesetzt werden, denn Matrixeffekte bewirken allzu starke Streuungen der Meßergebnisse. Es wird gezeigt, daß ein Zusatz von Ammoniumperoxodisulfat und Schwefelsäure zur Probenlösung eine deutliche Verbesserung bewirkt. Eine Routinemethode wurde entwickelt, bei der von diesem Effekt Gebrauch gemacht wird.

     

Abweichungen vom lokalen thermischen Gleichgewicht im axialen Kanal eines induktiv gekoppelten Argon-Plasmas

Summary Measurement of the excited state level population of a thermometric species like FeI injected into the axial channel of an inductively coupled plasma (ICP) is a powerful method to describe the plasma, even when the level population distribution in case of deviations from local thermal equilibrium (LTE) does not define a uniform plasma temperature.The injection of the thermometric species as ferrocene vapour allows to study the specific influence of operating conditions and normal sample components such as water on the plasma conditions by adding independently the different components.It is shown that deviations from LTE-state decrease with increasing generator power and decreasing carrier gas-flow rate and reach an axial minimum in the normal analytical zone (NAZ). Although differences of more than 1000 K between excitation temperature of low lying FeI-levels and levels close to the ionization-limit have been observed, deviation of the levels population density from an LTE-distribution is smaller than a factor of 5 under reasonable analytical conditions. Under such conditions the LTE-concept seems to be a useful first approximation to describe the thermodynamics of the ICP and to predict trends.

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Herrn Prof. Dr. Reinhard Nast zum 75. Geburtstag gewidmet     

Dynamics of quantum wave packets in complex molecules traced by 2D coherent electronic correlation spectroscopy

Electronic and nuclear molecular wavepackets are a clear manifestation of the wavelike properties of matter at the very heart of quantum mechanics. In this work we demonstrate how electronic two-dimensional spectroscopy (2D) serves as a highly evolved tool for the simultaneous investigation of both phenomena. In further analysis and theoretical treatments, 2D spectra form an ideal basis for the discussion of electronic decoherence, vibrational relaxation and electron-phonon coupling.     

Determination of heavy metals in sea water and in marine organisms by flameless atomic absorption spectrophotometry

Summary This publication is a part of a series in which the author describes a set of methods for the determination of cadmium in environmental samples by means of flameless AAS. Common properties of these methods are their miniaturization and standardization. These have been attained by the utmost reduction of the number of steps and by their simplification. The method described in this publication consists of an acid digestion procedure followed by neutralization, extraction, and flameless AAS measurement. The main characteristics are: digestion takes place in small 1.5 ml tubes of quartz, polyvinyldifluoride or polypropylene. Neutralization is not performed by titration but only by an excess of saturated NaHCO₃ solution. Extraction results are independent of pH in the region to be expected. Extraction is carried out by a (stable) solution of APDC in CCl₄. The organic extract is also stable for at least 16h. Precision of the method lies in the range of 8.4%, at a concentration of 18.9 ng Cd g^–1; sensitivity is at least in the range of 1.2 ng Cd g^–1. The latter can be increased, if necessary, by a several-step extraction procedure.Teil VIII: Z. Lebensm.-Unters. Forsch. 168, 193-194 (1979)     

Analysis of high-purity reagents using automatic on-line column preconcentration-separation and electrothermal atomic absorption spectrometry

Summary A fully automatic flow-injection on-line column preconcentration and separation procedure for electrothermal atomic absorption spectrometry is described for the determination of cadmium and lead in high-purity reagents. A microcolumn with 9 L of solid sorbent, introduction of air prior to elution, and use of methanol as the eluent made it possible to elute the sorbed analyte quantitatively with only 80 L of solvent. The total eluate volume was transferred into the graphite tube which was pre-heated to 80°C using a flow rate of 0.08 mL min^–1 which allowed the solvent to evaporate in part during eluate introduction. The efficiency of the total procedure was 0.63 and 0.65, and the enrichment factor was 62 and 64 for cadmium and lead, respectively, compared with the direct introduction of 30 L of an aqueous solution. The sample throughput was 13 h^–1 for a sample loading time of 60 s and the detection limits (3 ) were 0.7 and 4.5 ng L^–1 for cadmium and lead, respectively. The relative standard deviation of the entire procedure in the optimum working range was typically around 3% (n=6). A number of high purity (suprapure) and analytical grade (pro analysi) reagents were analyzed, and spiking experiments resulted in recoveries of 97–104%.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthdayOn leave from Jiangsu Institute of Petrochemical Technology, Changzhou, Jiangsu, China