Determination of glycols by HPLC with refractive index detection

A simple and fast HPLC method for the determination of glycols is described. It is characterized by a reversed-phase separation using water as eluent and a refractive index detection. The method was applied to investigate the biodegradation of glycols in a laboratory activated sludge plant and to determine the content of glycols or alcohols in detergents. The detection limit is 4 mg/l ethylene glycol or propylene glycol in an aqueous sample.     

Design,synthesis, and evaluation of 6-carboxyalkyl and 6-phosphonoxyalkyl derivatives of 7-oxo-8-ribitylaminolumazines as inhibitors of riboflavin synthase and lumazine synthase

A series of 6-carboxyalkyl and 6-phosphonoxyalkyl derivatives of 7-oxo-8-D-ribityllumazine were synthesized as inhibitors of both Escherichia coli riboflavin synthase and Bacillus subtilis lumazine synthase. The compounds were designed to bind to both the ribitylpurine binding site and the phosphate binding site of lumazine synthase. In the carboxyalkyl series, maximum activity against both enzymes was observed with the 3'-carboxypropyl compound 22. Lengthening or shortening the chain linking the carboxyl group to the lumazine by one carbon resulted in decreased activity. In the phosphonoxyalkyl series, the 3'-phosphonoxypropyl compound 33 was more potent than the 4'-phosphonoxybutyl derivative 39 against lumazine synthase, but it was less potent against riboflavin synthase. Molecular modeling suggested that the terminal carboxyl group of 6-(3'-carboxypropyl)-7-oxo-8-D-ribityllumazine (22) may bind to the side chains of Arg127 and Lys135 of the enzyme. A hypothetical molecular model was also constructed for the binding of 6-(2'-carboxyethyl)-7-oxolumazine (15) in the active site of E. coli riboflavin synthase, which demonstrated that the active site could readily accommodate two molecules of the inhibitor.     

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.

     

Thermische Zersetzung von Blei(II)-Acetat

Zusammenfassung Die Zersetzung von Pb(CH₃COO)₃ · 3 H₃O wurde im Bereich von Raumtemperatur bis 450° unter N₃ mittels TG, DTA verfolgt und die Produkte wurden analytisch charakterisiert. PbO ist das hauptsächliche feste Endprodukt, neben dem im wesentlichen nur Pb entsteht. Als feste Zwischenprodukte wurden neben Pb(CH₃COO)₃ die basischen Acetate Pb(CH₃COO)₂ · PbO und Pb(CH₃COO)₂ · 2 PbO gefunden und durch Röntgenpulveraufnahmen identifiziert; diese basischen Acetate wurden durch isotherme Zersetzung bei 240 bzw. 305° dargestellt. Unter den durch GC und MS erfaßten und quantitativ bestimmten flüchtigen Zersetzungsprodukten sind CO₂ und Aceton Hauptbestandteile. Verschiedene Bildungsweisen der übrigen Produkte, CH₃COOH, (CH₃CO)₂O, Acetylaceton und des Zwischenproduktes Keten werden aufgezeigt.

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The decomposition of Pb(CH₃COO)₃ · 3 H₂O under N₂ has been studied by TG and DTA between room temperature and 450° and the products have been characterized analytically. PbO is the main solid product, besides which essentially only Pb is produced. As solid intermediates, aside from Pb(CH₃COO)₃ the basic acetates Pb(CH₃COO)₂ · PbO and Pb(CH₃COO)₂ · 2 PbO have been found and identified via their X-ray powder diagrams; these basic acetates have been prepared by isothermal decomposition at 240 and 305°, respectively. Among the volatile decomposition products analyzed by GC and MS and determined quantitatively, CO₂ and acetone are the main products. Different routes for the formation of the other products, CH₃COOH, (CH₃CO)₂O, acetylacetone and the intermediate ketene are shown.

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Résumé On a suivi, par TG et ATD sous N₂, dans l'intervalle de températures allant de l'ambiante jusqu'à 450°, la décomposition de Pb(CH₃COO)₂ · 3 H₂O dont on a caractérisé les produits par des méthodes analytiques. PbO est le principal produit final solide, en dehors duquel il ne se forme essentiellement que du Pb. Comme produits intermédiaires solides, on a trouvé, à part Pb(CH₃COO)₂, les acétates basiques Pb(CH₃COO)₃. PbO et Pb(CH₃COO)₂ · · 2 PbO qui ont été identifiés par analyse de poudres aux rayons X. Ces acétates basiques se sont formés, par décomposition isotherme, respectivement à 240 et à 305°. Parmi les produits de décomposition volatils décelés par GC et MS et dosés par des méthodes quantitatives, CO₃ et l'acétone sont les composants principaux. On montre les différents modes de formation des autres produits, comme CH₃COOH, (CH₃CO)₃O, l'acétylacétone et le cétène formé transitoirement.

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Pb(CH₃COO)₂. 3₂O 450°. . PbO , , . , Pb(CH₃COO)₂, Pb(CH₃COO)₂. PbO Pb(CH₃COO)₂. 2PbO, . , , 240 305°. , -, CO₂ . , CH₃COOH, (CH₃CO)₂O, .

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Stimulated emission and laser action of Pr3+-doped YA1O3

Groundstate absorption, fluorescence, excited-state absorption, and stimulated emission of Pr:YA1O₃ were measured in dependence on the polarization. The results reflect the anisotropy of the host lattice. Especially the polarized spectra of the stimulated emission fit very well with the laser data of this material. Seven cw laser transitions in the visible spectral range obtained so far in Pr:YA1O₃ with argon-ion laser pumping were identified in the spectra of the stimulated emission. In addition, two infrared cw laser transitions were realized. The best results were achieved for the³ P ₀³ F ₄ laser transition at 746.9 nm with a maximum slope efficiency of 24.6%, a maximum output power of 49.6 mW, and a laser threshold of 25 mW.     

Geometry optimization in ab initio SCF calculations: Part IV. Energy barriers and dipole moments obtained with floating orbital geometry optimization (FOGO)

The floating orbital geometry optimization (FOGO) described previously is applied to H₂O₂, NH₃, HNC, HNO, HNCO, and CH₃OH. In the FOGO method we apply two analytically calculated energy gradients in a variable metric method. Some orbitals are no longer fixed on the corresponding nuclei, but their position is optimized simultaneously with the nuclear coordinates. It is shown that relative energies (e.g. rotational barriers) are obtained with similar accuracy to basis sets including polarization functions. Further, it is confirmed that FOGO yields excellent dipole moments. The FOGO method involves a considerable time saving compared to conventional calculations with DZ + P basis sets.     

CdO auf Cadmiumanoden in Alkalihydroxidlösungen??

Anodic films formed potentiostatically in 1M NaOH on Cadmium electrodes were examined by means of electron diffraction under carefully controlled conditions. Glancing incidence electron diffraction indicates the presence of Cd(OH)₂ on the electrolyte side of the film and of CdO on the metal side. Transmission electron diffraction of thin isolated films indicates only Cd(OH)₂ in films formed below the Flade-potential of the CdO electrode, but CdO along with Cd(OH)₂ above the Flade-potential. In these films selected area diffraction reveals spots consisting exclusively of a very thin oxid layer.     

Atomic absorption inhibition titration of orthophosphate and polyphosphates

The atomic absorption inhibition titration of phosphates was studied for two types of burner. Dependence on gas Flow-rates was observed. The method with a pre-mix burner was employed to determine phosphate in surface and waste waters. The results are compared with those by the standard method. The proposed method was found to be rapid, simple and accurate.