Bestimmung von Kupfer und Eisen in Milchfett aus einem Aufsehlu?

Zummmenfassung Aus Butter bzw. Butterreinfett wird im Kjeldahlkolben ein Salpetersäure-extrakt hergestellt und dieser mit Perehlorsäure aufgeschlossen. Nach Reduktion mit Hydroxylammoniumchlorid und Abpufferung auf pH 4,5 wird zunächst der Cu-Bathocuproin-Farbkomplex gebildet, mit Hexanol extrahiert und bei 479 nm bestimmt. Anschließend erfolgt die Bildung des Fe-Bathophenanthrolin-Komplexes und seine Messung bei 533 nm. Das ausgearbeitete Verfahren gestattet die Bestiimmung des Fe-Gehaltes in Butter (gefundene Werte: 0,11-0,45 ppm) und Butterreinfett (gefundene Werte: 0,05-0,25 ppm, in einem Einzelfall 1,94 ppm) und die Bestimmung des Cu-Gehaltes in Butter (gefundene Werte: 0,02-0,06 ppm) mit guter Sicherheit und Präzision. Eine genaue Bestimmung der äußerst geringen Cu-Konzentrationen, wie sie im Butterreinfett normalerweise vorkommen (unter 0,02 ppm), aus einer Untersuchungsprobe von etwa 20 g ist, wie bei allen photometrischen Verfahren auf der Grundlage der z. Z. verfügbaren Farbreagentien, nicht möglich, jedoch kann eine Überschreitung der heute bei 0,02-0,05 ppm angenommenen Toleranzgrenze für Cu in Butterreinfett guter Haltbarkeit leicht festgestellt werden.

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Estimation of copper and iron in butterfat from one digest.I. Photometric method

Summary The sample of butter or anhydrous butterfat is extracted with nitric acid in a Kjeldahi flask and the extract digested by perchloric acid. After reduction with hydroxylamine hydrochloride and buffering to a pH of 4,5 first the Cu-bathocuproine complex is formed, extracted with hexanol and photometrically measured at 479 nm. Then, likewise, the Fe-bathophenantholine complex is formed and estimated at 533 nm. The method allows the estimation of Fe in butter (concentrations found: 0.11-0.45 ppm) and anhydrous butteroil (concentrations found: 0,05-0,25 ppm, in one case: 1.94 ppm) and of Cu in butter (concentrations found: 0.02-0.06 ppm) with good security and precision. As with each photometric method based on the most sensitive Cu reagents now available, an accurate measurement of traces of Cu as usually present in anhydrous butteroil (less than 0.02 ppm) from a sample of about 20 g is not possible; however, exceeding of the tolerance level for butteroil of good keeping quality (at present assumed to be 0.02-0.05 ppm) can easily be detected.

     

Relationship between microstructure and mechanical properties of a spinodally decomposing Cu-15Ni-8Sn alloy prepared by spray deposition

A spinodally decomposing alloy of composition Cu-15 wt pct Ni-8 wt pct Sn processed by Osprey spray deposition was examined and the principal factors determining strength and ductility studied. Strengthening contributions are shown to arise from grain-size reduction by controlled recrystallization, and from the internal stress fields created by spinodal decomposition. Discontinuous precipitation takes place after the completion of spinodal decomposition and is partly responsible for the decrease of yield stress after such prolonged aging. At the same time, there is some loss of ductility, but the discontinuous precipitation is not believed to be the main cause. Instead, it is the appearance of additional phases, such as Ni₃Sn, in the matrix that is considered to be the main cause of the brittleness.     

Ethylene hydrogenation mechanism on Ag/SiO2 catalysts elucidated by isotope kinetics

On a highly dispersed Ag/SiO₂ catalyst the reaction of ethylene with hydrogen was studied by means of isotopic exchange. Although hydrogenation does not proceed below 550 K, a latent but intensive interaction between ethylene and hydrogen could be observed already at 480 K. On the investigated catalyst the mechanism of the ethylene hydrogenation is similar to that known for nickel, the catalytic behaviour, however, being distinctly different.     

Engineering disulfide-linked single-chain Fv dimers [(sFv')2] with improved solution and targeting properties: anti-digoxin 26-10 (sFv')2 and anti-c-erbB-2 741F8 (sFv')2 made by protein folding and bonded through C-terminal cysteinyl peptides

Single-chain Fv fusions with C-terminal cysteinyl peptides (sFv')have been engineered using model sFv proteins based upon the26-10 anti-digoxin IgG and 741F8 anti-c-erbB-2 IgG monoclonalantibodies. As part of the 741F8 sFv construction process, thePCR-amplified 741F8 V_H gene was modified in an effort to correctpossible primer-induced errors. Genetic replacement of the N-terminalp-strandsequence of 741F8 VH with that from the FR1 of anti-c-erbB-2520C9 VH resulted in a dramatic improvement of sFv folding yields.Folding in urea-glutathione redox buffers produced active sFv'with a protected C-terminal sulfhydryl, presumably as the mixeddisulfide with glutathione. Disulfide-bonded (sFv')₂ homodimerswere made by disulfide interchange or oxidation after reductiveelimination of the blocking group. Both 26–10 (sFv')₂and 741F8 (sFv')₂ existed as stable dimers that were well behavedin solution, whereas 741F8 sFv and sFv' exhibited considerableself-association. The 741F8 sFv binds to the extracellular domain(ECD) of the c-erbB-2 oncogene protein, which is often overexpressedin breast cancer and other adenocarcinomas. The recombinantECD was prepared to facilitate the analysis of 741F8 bindingsite properties; the cloned ECD gene, modified to encode a C-terminalSer-Gly-His₆ peptide, was transfected into Chinese hamster ovarycells using a vector that also expressed dihydrofolate reductaseto facilitate methotrexate amplification. Optimized cell linesexpressed ECD-His₆ at high levels in a cell bioreactor; afterisolation by immobilized metal affinity chromatography, finalECD yields were as high as 47 mg/l. An animal tumor model complementedphysicochemical studies of 741F8 species and indicated increasedtumor localization of the targeted 741F8 (sFv')₂ over othermonovalent 741F8 species.