Thermodynamic parameters for the molecular inclusion reaction of dulcin with beta-cyclodextrin. spectrofluorimetric determination of dulcin

The inclusion of dulcin in alpha- and beta-cyclodextrin has been studied by fluorescence spectroscopy. To quantitatively describe complex formation between the beta-cyclodextrin and dulcin, an association constant of 290 M(-1) at 21 degrees was obtained. The thermodynamics associated with the complex formation between dulcin and beta-cyclodextrin in aqueous solution has been studied. The obtained value of DeltaG(0) = -13.7 kJ/mole at 21 degrees , together with DeltaH(0) = -33.6 +/- 2.3 kJ/mole and DeltaS(0) = -67.2 +/-8.3 Jmole(-1) K(-1) indicate that dulcin has a very marked tendency to associate with beta-cyclodextrin in water. The inclusion complex of dulcin in beta-cyclodextrin has been used to determine dulein in the range 0.13-5 mug/ml the method has been applied to determine dulcin in soft drinks.     

Analysis of primary aliphatic short-chain monoamines by LC in water samples

Several derivatization procedures with o-phthaldialdehyde-N-acetylcysteine (OPA-NAC) were compared for a rapid analysis of primary aliphatic short-chain monoamines in water samples by HPLC using a LiChorospher analytical separation column (100RP₁₈ mm i.d., 5 μm). Both the solution and the solid-support assisted off-line derivatization on C₁₈ SPE cartridges were inadequate options because of beginning degradation processes of the instable isoindol derivatives during their transfer to the analytical column. This problem was precluded with the on-column or solid-support assisted on-line derivatization. In the last mentioned procedure, the derivatization took place in a Hypersil C₁₈ precolumn ( mm i.d., 30 μm) connected with an additional preconcentration step resulting in better detection limits (0.002-0.040 μg ml⁻¹ requiring only 150 μl of water sample) than in the on-column procedure (0.08-0.16 μg ml⁻¹). The improved sample handling, the better control of parameters affecting reaction rates, the fully automation of this method with only 10 min analysis time for each sample are further advantageous. The potential of the solid-support assisted on-line derivatization was outlined and applied to water samples from several sources. Recovery values near 100% were obtained.     

Hydration of acetylene on Cd2+ exchanged zeolites

The reaction takes place on Cd-containing Lewis sites, whereas the irreversible adsorption and condensation of product acetaldehyde on acidic OH groups of Cd-X, FAU catalyst results in deactivation. Preadsorbed ammonia moderates the deactivation, because it reacts with acetylene, and pyridine homologues are formed which block the accessible OH groups. Since in divalent cationic forms of clinoptilolite no OH groups are generated, Cd-clinoptilolite proved to be a catalyst of permanent activity.

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, Cd, — OH FAU, Cd-X. , .. , OH . OH, Cd- .

     

Properties and analytical applications of the heteropolymolybdates of phosphorus, arsenic, silicon and germanium-IV Determination of phosphomolybdic and silicomolybdic acids via the molybdenum content, with phenylfluorone

Procedures are proposed for the determination of phosphorus and silicon in the ppM range, by extraction of phosphomolybdic and silicomolybdic acids with organic solvent, decomposition of the complex and spectrophotometric determination of its molybdenum content.     

Complex study of nickel skeleton catalysts: V. Study of novel non-pyrophoric nickel skeleton catalysts by derivatograph

The structure and properties of non-pyrophoric skeleton catalysts prepared from NiSi, NiAlSi, NiMg and NiZn alloys have been studied—apart from other thermal methods—by means of the derivatograph.Our experimental results have contributed to the explanation of the non-pyrophoric behaviour of these catalysts. We demonstrated that the desorption of the hydrogen content in our catalysts is not accompanied by the oxidation of active nickel. This oxidation takes place only at higher temperatures, above 200°C, at a rate proportional to the amount of active nickel.Other constituents of the catalysts (adsorbed water, hydroxide content) were also determined from the experimental data. The outstandingly high Mg(OH)₂ content of the NiMg catalyst indicates that its structure is dissimilar: Mg(OH)₂ also acts as support for the catalyst.     

L X-ray production cross sections, average L shell fluorescence yield and intensity ratios in heavy elements

L X-ray fluorescence cross sections, and intensity ratios were measured for elements in the 70￡Z￡92 atomic range at the excitation energy 59.5 keV using a Si(Li) detector. Furthermore, L X-ray fluorescence cross sections and intensity ratios were calculated for elements in the same range. The average L shell fluorescence yields were derived using experimental L X-ray fluorescence cross sections and theoretical photoionization cross sections. The obtained results were compared with other experimental and theoretical values. This revised version was published online in August 2006 with corrections to the Cover Date.     

Rapid determination of aliphatic amines in water samples by pressure-assisted monolithic octadecylsilica capillary electrochromatography-mass spectrometry

A pressure-assisted capillary chromatography-mass spectrometry method based on the use of a monolithic octadecylsilica (ODS) capillary is proposed for the determination of aliphatic amines. A 25 mM citric acid buffer containing 10% methanol is used as running electrolyte. Separation is achieved by simultaneously applying a capillary electrophoresis (CE) voltage of 13 kV and an overimposed pressure of 8 bar. The use of pressure is required to ensure stable electrospray conditions. Analysis times are reduced by using a capillary column consisting of a 30 cm long monolithic silica capillary column bound with ODS and a fused-silica capillary column also 30 cm long. The proposed method was successfully applied to the determination of low-molecular-weight aliphatic amines in tap and river water. The analysis of real samples requires cleanup and preconcentration, which can be performed automatically by inserting a minicolumn in the replenishment system of the commercial instrument.     

Twofold discretization and reconstruction of an infinite radiation field

Discretization method for unfolding Fredholm equation of the first kind is suggested for the reconstruction of an infinite monoenergetic radiation field scanned by a directional detector. The method is readily applicable for scanning carried out in planes with constant radial angles.     

Reconocimiento de nicotina en una hebrita de tabaco

Summary Adaption of theLuís method for the detection of nicotine to microscale, usingEmich's capillary technic proved successful, attaining identification limit of 0,03g.Applying a sub-micro steam distillation effect, the nicotine in a speck of tobacco (1 mm² and less) could still be detected by using the above reaction.Extension of the above procedure to mixtures of nicotine with substances not volatile with steam, inorganic (halides) as well as organic compounds (other alkaloids, acids, etc.) proved to be successful, even when the nicotine is present in proportions of only 1 part in 1000.

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Zusammenfassung Die Anwendung der Kapillartechnik vonEmich zum Nachweis von Nikotin nachLuís war erfolgreich und zeigte eine Erfassungsgrenze von 0,03g.Bei Anwendung einer Ultramikrodampfdestillation kann das Nikotin nach obiger Methode noch in Spuren von Tabak (1 mm² und weniger) nachgewiesen werden.Die Reaktion ist auch positiv bei Gemischen von Nikotin mit anderen, mit Wasserdampf nicht flüchtigen sowohl anorganischen (Halogenide) als auch organischen Substanzen (andere Alkaloide, Säuren etc.), selbst dann noch, wenn das Nikotin bloß im Verhältnis von 11000 vorhanden ist.

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Résumé La technique capillaire d'Emich a été utilisée avec succès pour identifier la nicotine suivant le procédé deLuís; la limite de sensibilité est alors de 0,03g. La mise en oeuvre d'un ultramicroentraînement à la vapeur permet en outre, par application de la précédente méthode, d'identifier la nicotine dans des traces de tabac (moins de 1 mm²). La réaction est également positive en présence d'autres substances non entraînables par la vapeur d'eau, qu'elles soient minérales (halogénures) ou organiques (autres alcaloïdes, acides, etc. ...) même si la proportion de nicotine n'est que de l'ordre de grandeur de 1/1000.