Potenzreihen mit mehrfach monotonen Koeffizienten

Ohne Zusammenfassung     

Spezielle analytische Methoden für die Arbeitsmedizin und Industriehygiene

With reference to earlier methods hexamethylene diisocyanate is saponified to hexamethylenediamine in acid solution, which is reacted with 1-fluoro-2,4-dinitrobenzene at both amino groups. The reaction product formed is extracted from the aqueous phase by chloroform and is photometrically measured against a corresponding blank value. Essential errors of earlier methods could be avoided. It is shown that Lambert's and Lambert-Beer's laws are obeyed and that the reaction with 1-fluoro-2,4-dinitrobenzene is quantitative at both amino groups of the diamine. Under the conditions described equimolecular amounts of hexamethylenediamine and hexamethylene diisocyanate yield the same absorbance. Absorption is quantitative. Amounts of 1–1000 μg of hexamethylene diisocyanate can be determined. The method cannot be applied to addition products on the basis of hexamethylene diisocyanate.     

Analytische Bestimmung der Darstellungsanzahlen natürlicher Zahlen durch spezielle ternäre quadratische Formen mit Kongruenzbedingungen

Ohne Zusammenfassung     

Determination of Iron in Caco-2 cells by ET-AAS

An electrothermal atomic absorption spectrometric method (ET-AAS) was developed for the direct determination of iron in intestinal Caco-2 cells after studying cell viability and proliferation using 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyl tetrazolium bromide (MTT test). Zeeman background correction and end-capped graphite tubes with Lvov platforms were used. Samples were dissolved in dimethylsulfoxide (DMSO) and pipetted directly into the graphite tube. The preashing, pretreatment and atomization steps were optimized. The temperatures selected were 600, 1200, and 2100 °C, respectively. Stability measurements were performed using iron standard solutions in DMSO on the one hand and acidified cell solutions on the other. Direct measurement and standard addition were compared in order to determine possible influences of the matrix. The low detection limit of the ET-AAS method (1.3 g/L or 3.3 g/g) combined with the small sample quantities required are ideal for the determination of iron in cells due to the low iron content and the limited growth area of the cells. The method was developed for iron uptake studies for toxicological purposes.     

Aryl cation and carbene intermediates in the photodehalogenation of chlorophenols

The photochemistry of 2,6-dimethyl-4-chlorophenol (6) has been studied in methanol and trifluoroethanol (TFE) through product studies and transient absorption spectroscopy. Chloride loss from triplet 6 gave triplet hydroxyphenyl cation 14, which equilibrated with triplet oxocyclohexadienylydene 15 within a few tens of nanoseconds; the cation can, however, be selectively trapped by allyltrimethylsilane (k(ad) = 10(8)-10(9) m(-1) s(-1)) to give a phenonium ion and the allylated phenol. In neat alcohols, 14 and 15 are reduced through different mechanisms, namely by hydrogen transfer through radical cation 17 and via phenoxyl radical 16, respectively. The mechanistic rationalization has been substantiated by the parallel study of an O-silylated derivative. The work shows that the chemistry of the highly (but selectively) reactive phenyl cation 14 can not only be discriminated from that of the likewise highly reactive carbene 15, but also exploited for synthetically useful reactions, as in this case with alkenes. Photolysis of electron-donating substituted halobenzenes may be the method of choice for the mild generation of some classes of phenyl cations.     

Mikroanalytische Bestimmung von Chlor (Brom) und Schwefel in organischen Verbindungen in einer Einwaage

Zusammenfassung Bei der maßanalytischen Bestimmung von Chlorid(Bromid)ionen wird ein exakter und farbkräftiger Umschlag erzielt, wenn mit isopropanolisoher Silberperchloratlösung in mindestens 80%igem Isopropanol titriert und Dichlorfluoreszein als Neutralisations- und Adsorptionsindikator angewendet wird. Eine vorhergehende Sulfattitration nachH. Wagner stört unter diesen Bedingungen nicht, so daß Chlor (Brom) und Schwefel in einer Einwaage schnell und sicher bestimmt werden können.

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Summary A precise and color-intensive change is obtained in the titrimetric determination of chloride (bromide) ions, if the titration is made with isopropanolic silver perchlorate solution in not less than 80% isopropanol, and if dichlorofluorescein is used as neutralization- and adsorption indicator. Under these conditions, no interference is encountered because of a preliminary sulfate titration afterH. Wagner, so that chlorine (bromine) and sulfur can be determined quickly and accurately in a single sample.

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Résumé Lors du titrage des ions chlorure ou bromure on obtient un virage exact et très coloré en effectuant le dosage avec une solution isopropanolique de perchlorate d'argent titrant au moins 80% en isopropanol en présence de dichlorofluorescéine comme indicateur de neutralisation et d'adsorption. Un titrage préalable des sulfates d'aprèsH. Wagner⁵ ne gêne pas, dans ces conditions, de sorte qu'il est possible de déterminer rapidement et sûrement le chlore (le brome) et le soufre sur un seul prélèvement analytique.