A rapid enrichment method for the analysis of traces of metals in aqueous solutions

Summary For the determination of traces of heavy metals e. g. from distilled water, drinking water or waste water generally a suitable pretreatment of the samples is necessary. For this reason an enrichment method was developed which makes it possible to precipitate several metals together with carrier elements from aqueous solutions. To carry out the method, 10 to 500 ml of the sample are mixed with 1 ml of a diluted nitric acid to produce a weak acid starting state for the diverse samples. After addition of a reduction solution and the collector solution the metals are precipitated at a constant pH between 5.0 to 5.5 with diethylammonium-N,N-diethyldithio-carbamate. The precipitate can be collected by filtration on a membrane filter. It forms a thin layer on the membrane filter and adheres without any auxiliary products for a long time. The time required for the complete process is less than 15 minutes if the starting volume was about 100 ml. A special equipment is not necessary. In the determination of traces of metals from organic substances a special rapid decomposition method with the decomposition device BIOKLAV^® was developed. By this method it is possible to convert the organic matter into an aqueous solution without addition of any chemicals. The BIOKLAV is a cylindrical pressure vessel with a safety rapid lock. A 20 g sample of organic material, e. g. meat or similar foodstuff, with a water content of 70–80% is pre-dried in the closed vessel and thereafter burnt in oxygen with elevated pressure. After this procedure all traces of metals present in the starting sample are contained in an aqueous solution consisting on the condensed water from drying and the burning products of the organic matter. The time required for the complete process is less than 30 min. From the obtained solution traces of metals are to enrich by precipitation with carbamate. The determination of the traces of metals is possible by a suitable method of analysis like atomic absorption, ICP or X-ray fluorescence. In various water samples, like drinking water and waste water, traces of Cr, Ni, Fe, Cu, Zn, Cd, Pb, As, Hg and Se in amounts of 5–100g were determined. The recovery rate was 80–90%. In organic substances Hg, Cd, Pb and As in amounts ranging from 50–250 ng/g resp. in amounts of 1–5g were detected with recoveries of more than 80%.

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Ein schnelles Anreicherungsverfahren zur Bestimmung von Schwermetallspuren in wärigen Lösungen

Zusammenfassung Zur Bestimmung von Schwermetallspuren z. B. in destilliertem Wasser, Trinkwasser oder Abwasser ist im allgemeinen eine geeignete Probenvorbereitung erforderlich. Für diesen Zweck wurde ein Anreicherungsverfahren ausgearbeitet, um gleichzeitig mehrere Metalle zusammen mit Spurenfänger-elementen aus wäßrigen Lösungen ausfällen zu können. Danach werden 10–500 ml Probenlösung mit 1 ml verd. Salpetersäure versetzt, um bei den verschiedenen Proben jeweils einen schwach sauren pH-Wert einzustellen. Anschließend werden eine Reduktionslösung sowie die Spurenfängerlösung zugegeben und mit einer Pufferlösung ein pH von 5,0–5,5 eingestellt. Die gelösten Metallspuren werden mit Diäthylammonium-N,N-diäthyldithio-carbamat ausgefällt. Der Niedersclhlag wird auf einem Membranfilter gesammelt. Man erhält ohne Hilfsmittel einen dünnen elastischen Film, der lange Zeit auf dem Filter haftet. Bei einem Ausgangsvolumen von 100 ml dauert der gesamte Vorgang weniger als 15 min. Für die Bestimmung von Metallspuren in organischen Substanzen wurde ein Schnellaufschlußverfahren mit dem Aufschlußgerät BIOKLAV^® entwickelt. Damit ist es möglich, die organische Matrix ohne Zusatz von Chemikalien in eine wäßrige Lösung zu überführen. Der BIOKLAV ist ein zylindrisches Druckgefäß mit einem Sicherheitsschnellverschluß. 20 g Probenmaterial mit einem Wassergehalt von 70–80%, z. B. Fleisch oder ähnliche Lebensmittel, werden im geschlossenen Gefäß zuerst vorgetrocknet und anschließend in Sauerstoff bei erhöhtem Druck verbrannt. Nach dem Aufschluß befinden sich die zu erfassenden Metallspuren in einer wäßrigen Lösung, die aus dem kondensierten Wasser des Probenmaterials und den Verbrennungsprodukten der organischen Matrix herrührt. Der gesamte Aufschluß dauert weniger als 30 min. Aus der Lösung können die Metallspuren durch Fällung mit Carbamat angereichert werden. Die Bestimmung der Elementspuren erfolgt z. B. mit Atom-Absorptions-Spektrometrie (AAS), Optischer Emissions-spektrometrie mit Plasma-Anregung (ICP) oder Röntgen-Fluoreszenz-Analyse(RFA). In verschiedenen Wasserproben, wie z. B. Trinkwasser und Abwasser wurden Spuren von Cr, Ni, Fe, Cu, Zn, Cd, Pb, Hg und Se in Mengen von 5–100g bestimmt. Die Wiederfindungsrate war 80–90%. In organischen Substanzen wurden Hg, Cd, Pb und As in Massenanteilen von 50–250 ng/g bzw. in Mengen von 1–5g mit einer Wiederfindungsrate von mehr als 80% bestimmt.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

Solvation Dynamics of a Radical Ion Pair in Micro‐Heterogeneous Binary Solvents: A Semi‐Quantitative Study Utilizing MARY Line‐Broadening Experiments

This work aims at elucidating the mechanism of solvation of a radical ion pair (RIP) in a micro‐heterogeneous binary solvent mixture using magnetically affected reaction yield (MARY) spectroscopy. For the exciplex‐forming 9,10‐dimethylanthracene/N,N‐dimethylaniline system a comparative, composition‐dependent MARY line‐broadening study is undertaken in a heterogeneous (toluene/dimethylsulfoxide) and a quasi‐homogenous (propyl acetate/butyronitrile) solvent mixture. The half‐saturation field extrapolated to zero‐quencher concentration, B_1/2, and the self‐exchange rate constants are analyzed in the light of solvent dynamical properties of the mixtures and a dielectric continuum solvation model. The dependence of B_1/2 on the solvent composition is explained by cluster formation giving rise to shortened RIP lifetimes. The results are in qualitative agreement with the continuum solvation model suggesting that it could serve as a theoretical basis for quantitative modeling.     

Two-dimensional slices of nonpseudoconvex domains with rough boundary

For a domain \(D\subset {\mathbb C}^n,\; n\ge 3\) , the set \(E\) is defined as the set of all points \(z\in {\mathbb C}^n\) for which the intersection of \(D\) with every complex \(2\) -plane through \(z\) is pseudoconvex. For \(D\) nonpseudoconvex, it is shown that \(E\) is contained in an affine subspace of codimension \(2\) . This results solves a problem raised by Nikolov and Pflug.     

Unendliche gefaserte steinersysteme

Ohne ZusammenfassungHerrn W. BURAU zum 70. Geburtstag gewidmet     

Orthomodulare Verbände mit Regularitätsbedingungen

Ohne Zusammenfassung     

Demonstration of image-zooming capability for diffractive axicons

Diffractive axicons are optical components producing achromatic nondiffracting beams. They thus produce a focal line rather than a focal point for classical lenses. This gives the interesting property of a long focal depth. We show that this property can be used to design a simple imaging system with a linear variable zoom by using and translating a diffractive axicon as the only optical component.     

A cheap metal for a "noble" task: preparative and mechanistic aspects of cycloisomerization and cycloaddition reactions catalyzed by low-valent iron complexes

Reaction of ferrocene with lithium in the presence of either ethylene or COD allows the Fe(0)-ate complexes 1 and 4 to be prepared on a large scale, which turned out to be excellent catalysts for a variety of Alder-ene, [4+2], [5+2], and [2+2+2] cycloadditon and cycloisomerization reactions of polyunsaturated substrates. The structures of ferrates 1 and 4 in the solid-state reveal the capacity of the reduced iron center to share electron density with the ligand sphere. This feature, coupled with the kinetic lability of the bound olefins, is thought to be responsible for the ease with which different enyne or diyne substrates undergo oxidative cyclization as the triggering event of the observed skeletal reorganizations. This mechanistic proposal is corroborated by highly indicative deuterium labeling experiments. Moreover, it was possible to intercept two different products of an oxidative cyclization manifold with the aid of the Fe(+1) complex 6, which, despite its 17-electron count, also turned out to be catalytically competent in certain cases. The unusual cyclobutadiene complex 38 derived from 6 and tolane was characterized by X-ray crystallography.     

A Novel Interface for Optimized Coupling of Gas Chromatography and Supersonic Jet Spectroscopy

The laser-based methods Laser Induced Fluorescence (LIF) and Resonance-Enhanced Multi-Photon Ionization (REMPI) can be used as highly selective detection modes for gas chromatography (GC). One major prerequisite for successful application of these detection methods is the availability of appropriate and reliable interfaces between the GC effluent and the molecular beam inlet. When a pulsed supersonic molecular beam (jet) source is used, the analyte molecules are efficiently cooled, allowing maximum selectivity of the laser spectroscopic detection methods. However, several technical problems have to be solved for practical realization of a GC-supersonic jet valve hyphenation. The pulsed jet interface should not interfere with the GC properties and the supersonic molecular beam properties. Further a good working cycle for the conversion from the continuously flowing GC current to the pulsed jet gas flow should be attained. This paper presents a novel setup of a GC-pulsed jet interface. The construction allows temporal and spatial compression of the analyte molecules in jet gas pulse and thus an increase of the detection sensitivity. Moreover, the GC effluent comes into contact only with glass surfaces and not with valve parts like plungers and seals. This reduces memory effects and sample decomposition. The valve setup is tested with a REMPI-TOFMS instrument.