Aufschlu?verfahren zur Analyse der Alkylphenolkomponente in Alkylphenolpolyglykol?thern

Zusammenfassung Um die Polyglykolkette in oxalkylierten Alkylphenolen abzuspalten, werden diese in schmelzendem Kaliumhydroxid aufgeschlossen. Der Aufschluß entfernt die Polyglykolkette quantitativ, ohne die Alkylkette der Alkylphenole zu verändern. Die Alkylphenole werden isoliert und können nun mit den üblichen chromatographischen Methoden aufgetrennt werden. Ihre Strukturen lassen sich mit Hilfe von IR-, UV- und NMR-Spektren aufklären. Die Diskussion über die Spektren von Umsetzungsprodukten aus Butylphenol und Äthylenoxid sowie Propylenoxid belegt die Notwendigkeit einer solchen Abbaumethode.Herrn Prof. Dr. Werner Schultheis zum 70. Geburtstag gewidmet.     

An experiment on program development

As a contribution to programming methodology, the paper contains a detailed, step-by-step account of the considerations leading to a program for solving the 8-queens problem. The experience is related to the method of stepwise refinement and to general problem solving techniques.     

Bestimmung von Nanospuren Antimon in biologischer Matrix

Zusammenfassung Eine selektive Bestimmung von Antimon durch Atomabsorptionsspektrometrie ist durch elektrothermale Atomisierung von Antimonwasserstoff in einem Argonspülgasstrom möglich. Das Verfahren erfordert eine hohe und reproduzierbare Geschwindigkeit der Reduktion des Antimons zu Antimonwasserstoff in der wäßrigen Probelösung. Geeignete Bedingungen für diese Reduktion erreicht man, wenn man in der Lösung zunächst einen Komplex von Antimon(III) mit Äthylendiamintetraessigsäure bildet; dieser Komplex reagiert mit Natriumborhydrid in der geforderten Weise zu Antimonwasserstoff. Bei der Mineralisierung des organischen Materials ist auf genaue Temperaturführung zu achten.

---

Determination of nanotraces of antimony in biological samples

Summary High selectivity in measuring antimony by atomic absorption spectrometry is obtained by electrothermal atomisation of stibine in a stream of argon purging gas. This procedure requires a fast and reproducible reduction to stibine of the total antimony present in an aequeous solution. Optimum conditions for this reduction are reached by first transforming all antimony in the solution to an EDTA-chelate of antimony(III) which then reacts uniformly with sodium boron hydride to give stibine. Close temperature control is essential in decomposition of biological samples.

     

Preconcentration of samples in sandwich tanks for continuous thin-layer chromatography

It is demonstrated that horizontai sandwich tank with two cover plates can be used to preconcentrate sample solutions. Narrow sharply-defined starting zones are obtained just outside the smaller cover plate when the series of spots of the sample solution are applied on the thin layer and predeveloped with a volatile solvent. After evaporation of the solvent, the whole area of the TLC-plate is covered with two plates and developed with a suitable solvent.     

Photometric method for the determination of nitrite in aqueous solutions and in blood

Summary The sensitivity of the hitherto known determinations of nitrite by formation of azo dyes and photometric measurement in aqueous solution is limited by the concentration of nitrite. In the method described here the azo compound formed is extracted into toluene and trichloroacetic acid is added to the extract. Immediately after addition of the latter the colour intensity reaches its maximum and is measured at 560 nm. In this way the sensitivity is made independent of the nitrite concentration in the aqueous solution and is limited only by the sample volume available.This study was supported by Deutsche Forschungsgemeinschaft.     

A Feigenbaum sequence of bifurcations in the Lorenz model

For some high values of the Rayleigh numberr, the Lorenz model exhibits laminar behavior due to the presence of a stable periodic orbit. A detailed numerical study shows that, forr decreasing, the turbulent behavior is reached via an infinite sequence of bifurcations, whereas forr increasing, this is due to a collapse of the stable orbit to a hyperbolic one. The infinite sequence of bifurcations is found to be compatible with Feigenbaum's conjecture.     

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

Summary In natural waters, heavy metals such as Cd may be present in bound form. It is, therefore, important to consider chemical speciation, especially at low concentrations of the metal where a significant part can be bound by other trace constituents so tightly that it escapes several forms of its determination. It has been demonstrated that even the very strong complexant APDC is unable to leach out all of the heavy metal present in several coastal water samples from the German Bight.This paper describes a new micro method for the determination of total Cd in natural waters. First a small sample is dried in a polypropylene vial. Then the salt residue is heated to 90° C with a mixture of sulphuric and nitric acid for digestion of organic trace constituents (and oxidation of sulphides if present). After dilution subsamples are neutralized using an excess of NaHCO₃ buffer solution. Extraction results are then independent from the possible slight variations of pH. The extractant, a solution of APDC in CCl₄ is stable for weeks, and even the extract is stable for at least 16h. Precision is in the range of 7% at a concentration of 0.066 g Cd l^–1; the detection limit is below 0.002 g l^–1 and can be lowered, if necessary, by enlargement of the original sample. According to the sensitivity of the method the typical blank of 0.022 g Cd l^–1 is high, but it is rather constant (mean variation from the mean: 0.0024 g l^–1).Teil XI: Fresenius Z. Anal. Chem. 299, 206–207 (1979)     

Stationary phases for gas chromatography; chemical stability of polysiloxanes

A number of polysiloxanes have been shown to be sensitive to acids when dissolved in chloroform. At 26O°C polysiloxanes were found to degrade under the influence of several compounds used or produced during the preparation of glass capillary columns.