M?glichkeiten und Grenzen der Identifizierung von Stoffen aus ihrem Verhalten bei der isothermen Eluierungsgaschromatographie

Zusammenfassung Es wird vorgeschlagen, für die Identifizierung von Stoffen Verteilungskoeffizienten zu verwenden und diese mit Hilfe der GLC in einem einfachen Verfahren, das auch die Kontrolle der Meßbedingungen erlaubt, zu bestmimen. Dieser Vorschlag kombiniert ein relatives Meßverfahren mit der Bestimmung absoluter Größen. Der Meßgenauigkeit, die für die Identifizierung von entscheidender Bedeutung ist, wurde besondere Aufmerksamkeit gewidmet und dabei herausgestellt, daß sie im allgemeinen durch die Trennleistung der Säule begrenzt wird. Für die Auswertung der Ergebnisse bei der Verwendung von Säulen mit verschiedenen stationären Phasen wurde ein Verfahren erprobt, bei dem die an den verschiedenen Säulen gemessenen Verteilungskoeffizienten miteinander kombiniert werden. Es wurde eine Tabelle der Verteilungskoeffizienten von etwa 80 Kohlenwasserstoffen bei 50,0° C mit Squalan und Dinonylphthalat als stationären Flüssigkeiten angefertigt. An Hand dieser Tabelle wurde die Identifizierung der C₅–C₇-Kohlenwasserstoffe eines Crackproduktes durchgeführt.

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Summary It is recommended to use partition coefficients for the identification of compounds and to determine these by a simple gas-chromatographic procedure, which allows the control of the measuring conditions.This recommendation combines a relative method of measurement with the determination of absolute quantities. The accuracy of the measurement, which is decisive for the identification, was investigated and it was found that the accuracy in most cases will be limited by the resolving power of the column. For the evaluation of the results obtained with columns with different stationary phases a method was tested in which the partition coefficients measured on two different columns were combined. A table of partition coefficients of 80 hydrocarbons at 50,0° C on squalane and dinonylphthalate as stationary phases was compiled. On the basis of this table the identification of the C₅-C₇ hydrocarbons in a crack product was carried out.

     

Li‐doped nanosized TiO2 powder with enhanced photocalatylic acivity under sunlight irradiation

This work reports on the synthesis of Li‐doped TiO₂ nanoparticles using the sol–gel process and solid‐state sintering, and investigates their potential use as a photocatalyst for degradation under sunlight excitation of different organic model compounds in aqueous solution. The structure of the nanocrystals was examined by X‐ray diffraction, UV‐vis ground state diffuse reflectance absorption spectra and X‐ray photoelectron emission spectroscopy. Results showed that samples prepared by sol–gel process and calcined at 400 °C are composed of a mixture of anatase and rutile phases, in contrast to the one prepared by solid‐state sintering, which exhibits an anatase phase with Li being involved in a spinel phase. The photocatalytic degradation of aqueous solutions of different aromatic compounds was successfully achieved under sunlight excitation in presence of Li‐doped TiO₂ prepared via sol–gel process. It was shown that the calcination temperature and the preparation mode greatly affect the photocatalytic efficiency. Copyright © 2010 John Wiley & Sons, Ltd.     

Methods for the efficient quantification of fruit provitamin A contents

As part of a screening program to identify micronutrient-rich banana and plantain (Musa) varieties, a simple, robust, and comparatively rapid protocol for the quantification of the provitamin A carotenoids contents of fruit pulp and peel tissues by HPLC and by spectrophotometry has been developed. Major points to note include the use lyophilisation and extensive tissue disruption procedures to ensure quantitative recoveries, and the avoidance of saponification and/or concentration steps which lead to significant losses of provitamin A carotenoids. The protocol showed excellent reproducibility between replicate extractions, without the need for an internal standard. Application of the methodology demonstrated that Musa fruit pulp has a relatively simple provitamin A carotenoids content, quite different from the overlying peel, and that the proportions of alpha- and beta-carotene are characteristic for each genotype. The protocol was also used to profile the provitamin A carotenoids of several other fruits.     

GC Comparative Analysis of Leaf Essential Oils from Two Myrtle Varieties at Different Phenological Stages

The essential oils obtained from leaves of two Myrtus communis varieties (baetica and italica), growing wild in North Tunisia, were investigated by GC and GC–MS at their different phenological stages. The highest essential oil yield was observed at the flowering stage with 0.6% (w/w) for italica and 0.4% (w/w) for baetica and 49 compounds were identified. The main essential oil leaf compounds of both myrtle varieties, belonging to the monoterpene class, were α-pinene, 1,8-cineole, limonene and linalool and their percentages showed significant changes during the phenological stages.

     

On the Number of Restricted Prime Factors of an Integer

Let \({q\geqq2}\) be an integer and denote S(n) the sum of the digits in base q of the positive integer n. Our main result is to estimate the sum \({\Sigma_{n\leqq x}\tilde{\omega}(n)}\) where \({\tilde{\omega}(n)}\) is the number of distinct prime factors p of n such that \({S(p) \equiv a \,{\rm mod} \,b \,(a \in \mathbb{Z}, b\geqq 2)}\) .     

Ladder-type P,S-bridged trans-stilbenes

Phosphole-containing π-systems have emerged as building blocks with enormous potential as electronic materials because of the tunability of the phosphorus center. Among these, asymmetric P-bridged trans-stilbenes are still rare, and here an elegant and efficient synthesis toward such fluorescent molecular frameworks is described. Fine-tuning of the photophysical properties is attempted by enforcing the planarization of the phosphorus tripod and thus increasing the interaction between the phosphorus lone pair and the π-system. The electronic structure of the π-conjugated frameworks is analyzed with NMR, UV-vis and fluorescence spectroscopy, and time-dependent density functional theory (TD-DFT) calculations.     

The selectivity of the stationary liquid in vapour phase chromatography

Vapour phase chromatography is a highly efficient analytical technique for the separation of gases and volatile liquids. The stationary phase in this percolation process is a liquid supported by an inert solid carrier material of a suitable particle size. The important role played by this liquid in the separation of a mixture into its components is discussed.     

A systematic evaluation of protocols for a proteomics analysis of (lyophilized) fruit tissues

This study represents a systematic evaluation of protocols for protein extraction and cleanup for fruit proteomic analysis. Procedures were optimized using pooled lyophilized banana fruit pulp, which is known to be particularly tricky due to high concentrations of soluble polysaccharides, phenolics, and other substances that interfere with protein extraction and purification. A total of 18 combinations of three protein extraction procedures (SDS‐based, Triton X‐100‐based, and phenol‐based), three protein precipitating agents (ammonium acetate/methanol, TCA/acetone, and acetone), and two resolubilization buffers (classical Rabilloud and the so‐called R2D2) were compared for total protein yields and efficiency of recovery. The results demonstrate that while losses in total recovered protein are unavoidable, the degree of these losses depends on the method combinations used. Combinations based on buffer‐saturated phenol always gave the highest yields, and overall recovery and purity was highest when acetone was combined with the R2D2 buffer for protein purification and concentration. Comparative 2D‐PAGE analysis confirmed that this method combination produced high‐quality and reproducible gels and the largest numbers of spots per gel. The usefulness of this methodology was demonstrated on ripe fruits from several other species and shown to give excellent results.     

Fortschritte der Gaschromatographie

Ohne Zusammenfassung