The analysis of combustion products : The polarographic determination of the lower organic peroxides

Some lower alkyl and acyl hydroperoxides and dialkyl peroxides have been prepared and their $\text{built}\text{i}{}_{\mathrm{<mtext>d</mtext>}}\text{c}$ values and halfwave potentials have been determined. The halfwave potentials become successively less negative on passing from hydrogen peroxide up the series, the order beingH₂O₂, CH₃OOH, EtOOH, (CH₃)₃COOH, R-CO(OOH)The limiting diffusion currents have been shown to be proportional to the concentrations of individual peroxides, and to be additive in mixtures. Methods have been developed which permit the detailed analysis of mixtures of peroxides containing, for example, hydrogen peroxide, methyl-, tert.-butyl and acetyl hydroperoxides, and diethyl peroxide. The effect of aldehydes has been investigated.     

The analysis of combustion products : The effect of hydrogen peroxide on the reaction of potassium permanganate with organic peroxides in acid solution

Although methyl and ethyl hydroperoxides alone do not react with potassium permanganate in acid solution at room temperature, they can be oxidised by this reagent in the presence of hydrogen peroxide. The apparent equivalents (as compared with hydrogen peroxide) are much lower than usual but, in the presence of excess hydrogen peroxide, the titre due to the organic peroxide is proportional to its original concentration. This forms the basis of a simple titration method which, though empirical, is both rapid and accurate. Since t-butyl hydroperoxide does not react in this way, it may be possible to differentiate the higher peroxides from lower peroxides.     

The analysis of combustion products : The estimation of traces of methanol in the presence of formaldehyde

In the analysis of combustion products, the estimation of traces of methanol can be rendered difficult by the presence of excess formaldehyde. A method is described for separating the formaldehyde from methanol by treating the solution with sodium bisulphite, and then carrying out a Chromatographie separation on filter paper. Ether carries the methanol to the end of the strip, leaving behind formaldehyde and hydrogen peroxide. The paper is cut into pieces, which are separately extracted with water, and the solution oxidised. The formaldehyde so formed ib estimated in the usual way with chromotropic acid.     

The chromatographic analysis of organic peroxides

Organic peroxides can be identified by reversed-phase chromatography on siliconc-treated paper, a chloroform-ethanol-water mixture is used as solvent, and the spray reagent is acidified ferrous thiocyanate.Peroxides of low molecular weight are lost from the paper by volatilisation, these can be identified and estimated by vapour-phase chromatography.     

The analysis of combustion products : The use of infra-red spectrometry for following high temperature kinetics

For the detailed elucidation of reaction mechanisms it is not adequate merely to stop a reaction at various times and to analyse the resulting products as a function of time, since many side reactions may occur during chilling. More reliable deductions could be made if the variation with time of the concentration of individual rcactants could be determined within the reaction vessel at the reaction temperature. The purpose of the present communication is to discuss the possibility of using infra-red spectrometry for tills purpose.A number of problems are encountered in the application of the technique: it is found, for example, that only certain types of double beam spectrometers can easily be used. A special, sensitive method is finally described for following the formation, in situ, of carbon monoxide and other compounds in the slow oxidation of propane. The advantages and the possible applications and improvements are discussed in detail.     

对改进化学实验的几点建议

为了充分发挥化学实验在教学中的作用和提高课堂效率,教师在教学过程中有必要对所做的实验,从仪器的选择,药品的用量,实验装置及操作方法等方面,不断地加以改进。一、增强直观效果一个模糊不清的现象,不仅失去了对知识的说服力,还可能造成观察时的错觉,又常常引起课堂秩序的混乱。可见,改进实验时,首先应该重视如何提高直观效果。1.仪器的选择和药品的用量仪器的大小和用药的多少应以教室最后排学生能清楚地看到实验现象为标准。显然,反应容器大,药品用量多直观性就强。     

Critical study of and improvements in chromatographic methods for the analysis of type B trichothecenes

Various analytical methods used in the analysis of type B trichothecenes (deoxynivalenol, nivalenol, 3- and 15-acetyldeoxynivalenol) in cereals were compared and optimised in this work. These methods use either GC-electron-capture detection (ECD) of trimethylsilyl, trifluoroacetyl and heptafluorobutyryl derivatives or HPLC with UV or photodiode array detection of analytes. A new HPLC procedure using fluorescence detection prior derivatisation with coumarin-3-carbonyl chloride has been also tested. Five extraction solvents and two solid-phase extraction cartridges (silica, Florisil) plus a especial clean-up column (MycoSep 225) were compared in order to obtain the best recovery of the mycotoxins with minimal presence of coextractives in the chromatograms. The chosen extraction solvent was a mixture of acetonitrile-water (84:16, v/v). The MycoSep 225 column was chosen as the best alternative for clean-up of grain samples. For GC-ECD analysis, derivatisation of analytes with heptafluorobutyric anhydride prior the final determination was chosen as the most suitable procedure. HPLC-photodiode array (at 221 nm) analysis was more suitable for determination of type B trichothecenes than HPLC of the fluorescent coumarin-3-carbonyl derivatives. Recoveries obtained in spiked corn, rice and wheat are reported. The utility of the proposed methodology was assayed in cereal cultures of various Fusarium strains.     

Chemometric methods in NMR spectroscopic analysis of food products

The main achievements of high-resolution NMR spectroscopy in combination with different chemometric methods in the analysis of food products in the last 40 years are reviewed. The essence of chemometric methods used for the analysis and interpretation of NMR spectra is briefly described. Sample preparation for NMR-spectroscopic analysis is characterized. Methods for the mathematical treatment of NMR spectra (smoothing, Fourier transformation, bucketing, normalization, and selection of spectral ranges) are considered. Currently available methods for the suppression of the signals of macrocomponents, including those for the simultaneous suppression of several signals, are described. The results are illustrated based on examples of analysis of different classes of foodstuffs and beverages with the use of NMR spectroscopy and chemometric methods for classification and discrimination (geographical and botanical origin as well as validating checking the brand authenticity).     

The formation of toxic products during the combustion of halogen-containing polymers

Studies have been made of the decomposition of decabromobiphenyl and decabromobiphenyl ether both during the burning of polymers and under the less oxygen-rich conditions involved in the incineration of plastic waste material. The nature of the products depends on the type of combustion. During flameless combustion, the two flame-retardants volatilize unchanged. However, when polymer containing the additive burns with a flame, hydrogen bromide is the only significant bromine-containing product. Product distributions in flames above burning polymers show that the concentration of the hydrogen halide increases from zero at the molten polymer surface to a value corresponding to total conversion of the halogen at and beyond the flame front.     

Some problems associated with the chromatographic analysis of thiophene hydrodesulphurization products

Summary Adsorption of thiophene on the walls of stainless steel sample loops, even at relatively high temperatures (up to 180°C), is shown to result in significant errors in the chromatographic analysis of thiophene. A chromatographic system is described which allows a good separation of thiophene and C₄ hydrocarbons resulting from the catalytic hydrogenolysis of thiophene.     

The combustion—coulometric determination of sulphur in gaseous and liquid organic products

A combustion—coulometric procedure is described for the determination of sulphur in gaseous and liquid organic materials with a final boiling point below 550°C. Modifications to the original Dohrmann procedure concerning combustion, titration and removal of interfering compounds have resulted in a more stable and sensitive system capable of detecting 0.15 ng of sulphur. Concentrations of sulphur down to 0.03 mg kg^-1 can be determined within a few minutes.     

Some applications of thermal methods of analysis to polymers

Some examples are given of the application of thermogravimetry, differential scanning calorimetry, thermomechanical analysis, torsional braid analysis, stress relaxometry and dynamic viscoelastometry to the study of cross-linked polymer systems. The information derived by the use of each technique is outlined and the advantages and disadvantages of the different methods are compared.

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Zusammenfassung Einige Beispiele der Anwendung der Thermogravimetrie, Differential Scanning Kalorimetrie, thermomechanischen Analyse, Torsionsfadenanalyse, Streßrelaxometrie und dynamischen Viscoelastometrie zur Untersuchung quervernetzter Polymersysteme werden gegeben. Die an Hand des Einsatzes der einzelnen Techniken erhaltenen Informationen werden beschrieben und die Vor- und Nachteile der verschiedenen Methoden miteinander verglichen.

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Résumé On donne quelques exemples de l'application de la thermogravimétrie, de l'analyse calorimétrique différentielle (DSC), de l'analyse thermomécanique, de l'analyse au fil de torsion, de la mesure de la relaxation des tensions, de la viscoélastométrie dynamiques, à l'étude des polymères à réseau tri-dimensionnel. On souligne les renseignements obtenus en utilisant chacune de ces techniques et on compare les avantages et les inconvénients de ces différentes méthodes.

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Some improvements in the estimation of137Cs in urine by the AMP-chlorostannate method

An accurate and reliable method has been developed for the estimation of radiocesium in urine. Initially cesium is adsorbed on ammonium phosphomolybdaste (AMP) precipitate and separated by ion exchange from other contaminants. Cesium thus separated is estimated as cesium chlorostannate, Cs₂SnCl₆, from a 50 (v/v)% solution of concentrated HCl in ethyl alcohol. While the results are in good agreement with the values obtained by γ-spectrometry using a Marinelli beaker in its range of applicability, the present method has a much lower detection limit. It is observed that the method has significant advantages over the methods available with respect to analysis time, accuracy and detection limits.     

Transformation of solvent-derived ozonolysis products to bicyclic peroxides: Isolation and characterisation of novel pentoxonane derivatives

-Hydroperoxyisochroman derivatives 5 react with formaldehyde under acidic conditions to produce mixtures of bicyclic 1,2,4,6-tetroxepane 9 and 1,2,4,6,8-pentoxonane 10 derivatives. The structure of the compound 10a was unambiguously established by the X-ray analysis. With acetaldehyde, only the corresponding 1,2,4,6-tetroxepanes 9 were obtained.