HPLC-Electrochemical detection with graphite-poly (tetrafluoroethylene) electrode Determination of the fungicides thiram and disulfiram

The suitability of composite graphite-poly(tetrafluoroethylene) (Teflon) electrodes as amperometric indicator electrodes in HPLC detection is demonstrated. The determination of the fungicides thiram and disulfiram in the presence of ziram has been chosen as an analytical problem. The optimization of working conditions, such as the choice of the organic solvent used in the mobile phase as well as its percentage, the potential applied to the composite electrode, and the time elapsed between mixing the carbamates and the injection, has been accomplished by using the wall-jet flow-cell configuration. The effect of the acetonitrile percentage used in the mobile phase on the retention of thiram, disulfiram, ziram and phenol was evaluated. Resolution up to the baseline can be achieved with 45% acetonitrile. The sensitivity of the determination of thiram and disulfiram in the presence of a constant concentration of ziram is slightly better when using a wall-jet cell; however, the background current is higher, as well as the baseline noise and the time necessary to achieve stabilization of the baseline before the injection. Lower limits of detection for both fungicides, as well as a better repeatability, were obtained when using a thin-layer flow cell configuration. As an application, the determination of thiram in spiked apple samples, at a level of 0.5 mg thiram kg(-1) apple, has been carried out with a mean recovery of 97 +/- 3% for a significance level of 0.05.     

Über Reaktionen von Nitrosophenolen, 4. Mitt.: Reaktion von Nitrosonaphtholen mit Naphtholen

Zusammenfassung Die Reaktion von 1-Nitroso-2-naphthol mit 1-und 2-Naphthol sowie die Reaktion von 2-Nitroso-1-naphthol mit 2-Naphthol in Äthanol und in Äther bei Anwesenheit von HNO₃ gibt 5H-Dibenzo[a,j]phenoxazon-(5) (I), 5H-Dibenzo[a,j]phenoxazon-(5)-14-oxid (II), 5H-Dibenzo[a,h]phenoxazon-(5) (III) sowie 5H-Dibenzo[a,h]phenoxazon-(5)-14-oxid (IV). Es wurde ein Reaktionsmechanismus vorgeschlagen und die Konstitution der hergestellten Verbindungen spektrophotometrisch und potentiometrisch bestimmt.

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The reaction of 1-nitroso-2-naphthol with 2-and 2-naphthol and the reaction of 2-nitroso-1-naphthol with 2-naphthol in ethanol or ether in the presence of nitric acid have been studied. The main reaction products isolated were the dibenzophenoxazones I–IV. The reaction mechanism for their formation is proposed.

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Mit 4 Abbildungen     

Photodegradation of a 1,3,4-thiadiazole-urea herbicide. Isolation,characterization, X-ray crystal structure and synthesis of photoproducts

The photodegradation of 1,3-dimethyl-1-(2-(3-fluorobenzylthio)-1,3,4-thiadiazol-5-yl)urea as a thin film and in solution is described. The two photoproducts from thin-film photolysis were characterized by spectral and synthetic methods. The X-ray crystal structure of one of the photoproducts is also reported. The rearrangements were shown to involve an S-to-N benzyl migration, followed by a sulfur-oxygen substitution.     

The effect of mechanical activation on the thermal decomposition of chalcopyrite

Experimental results on the influence of preliminary mechanical activation on the thermal decomposition of chalcopyrite are presented and discussed. The following experimental facts were found:

Analyse theoretique des lois cinetiques couramment utilisees en thermoanalyse pour l'etude des reactions solid-gaz. III. proposition d'une nouvelle methode d'approche en regime dynamique

Résumé Dans la première partie de ce travail, les auteurs mettent en évidence que la vitesse d'une réaction en régime non isotherme dépend d'un facteur supplémentaire: le régime de montée en température. Cette assertion est basée sur le fait que le taux de réactionx est une fonction de trois variables: températureT, tempst, et vitesse de chauffeT, variable qui n'avait pas été prise en considération jusqu'ici par les autres auteurs travaillant sur ce problème.Puis, se basant sur les deux hypothèses suivantes: a) l'équation de vitesse en régime isotherme est la forme limite de l'équation de vitesse en régime dynamique, b) la variation de température en régime dynamique affecte la fréquence d'apparition des germes de la nouvelle phase, une formulation théorique des loisg(x) est proposée pour le régime non-isotherme. Cette formulation est explicitée en fonction de l'écart, à une température donnée, entre les valeurs de Lnk _i (isotherme) et Lnk _d (dynamique) dans le diagramme Lnk = f(1/T).L'étude, par thermogravimétrie, de la décomposition du gypse, du sulfate de calcium semihydraté, et de l'oxalate de calcium monohydraté, réalisée en montée linéaire de température, permet de vérifier expérimentalement la formulation théorique proposée.Pour obtenir une bonne interprétation cinétique d'une réaction chimique en régime dynamique, la vitesse de chauffe ne doit pas excéder 20°/heure.

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In the first part of this paper, the authors point out that the rate of reaction with non-isothermal kinetics depends on a supplementary factor: the heating rate. This assertion is based on the fact that the degreex of reaction is a function of three variables:T (temperature),t (time) andT (heating rate); this was not taken into account by other authors concerned with the subject.Then from the two following hypotheses: a) the rate equation for isothermal conditions is the limit form of the rate equation for non-isothermal conditions, b) the temperature change under dynamic conditions affects the frequency of nucleus formation of the new phase, a theoretical formulation of non-isothermalg(x) laws is proposed. This formulation involves the value of the difference, at constant temperature, between Ink _i (isothermal) and In k_d (dynamic) in the Ink=f(1/T) diagram.The thermogravimetric study of the dehydration of gypsum, of calcium sulfate hemihydrate, and of calcium oxalate monohydrate, under non-isothermal conditions, allows experimental verification of the theoretical formulation proposed.For a good kinetic approach of a chemical reaction under dynamic conditions, the heating rate must not exceed 20°/hour.

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Zusammenfassung Im ersten Teil dieser Arbeit wird von den Autoren bewiesen, daß die Geschwindigkeit einer Reaktion unter nicht-isothermen Bedingungen von einem zusätzlichen Faktor, den Bedingungen des Temperaturenstiegs, abhängt. Diese Behauptung beruht auf der Tatsache, daß der Reaktionsverlauf eine Funktion dreier Variablen ist: der TemperaturT, der Zeitt und der AufheizungsgeschwindigkeitT, wobei letztere Variable bisher von den auf diesem Gebiet arbeitenden Autoren außer Acht gelassen worden ist.Nachfolgend wird an Hand der zwei Voraussetzungen, daß a) die Geschwindigkeitsgleichung unter isothermen Bedingungen die Grenzform der Geschwindigkeitsgleichung unter dynamischen Bedingungen ist und b) die Temperaturänderung unter dynamischen Bedingungen sich auf die Erscheinungsfrequenz der Keime der neuen Phase auswirkt, eine theoretische Formulierung der Gesetzeg(x) für nicht-isotherme Bedingungen vorgeschlagen. Diese Formulierung wird als Funktion der Abweichung ausgedrückt, welche bei einer gegebenen Temperatur zwischen den Werten von Lnk _i (isotherm) und Lnk _d (dynamisch) im Diagramm Lnk=f(1/T) besteht.Die bei linearem Temperaturanstieg thermogravimetrisch durchgeführte Untersuchung der Zersetzung von Gips, von Calciumsulfat Semihydrat und von Calciumoxalat Monohydrat ermöglicht die vorgeschlagene theoretische Formulierung experimentell zu bestätigen.Um unter dynamischen Bedingungen eine gute kinetische Interpretation einer chemischen Reaktion zu erhalten, darf die Aufheizungsgeschwindigkeit den Wert von 20° pro Stunde nicht überschreiten.

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, : . , : (),t () ' ( ), , . : ) ) t(x) . Lnk _j () Lnk _d ( ) Lnk=f(1/T) . , , . , 20° .

     

Peroxides of higher aliphatic ethers

The oxidation of higher aliphatic ethers with oxygen at 50° yields two peroxides as the main oxidation products for each ether, namely a dihydroperoxy-dialkyl ether and a dihydroperoxy-dialkyl peroxide. The mass spectra of these compounds are recorded and the main fragmentation pattern is discussed.     

The kinetics of radical polymerization—XXVII. Investigation of the radical reactivity of 3,3′- and 4,4′-disubstituted azobenzenes in the polymerization of vinylacetate

A study was made on the inhibition by some 3,3′- and 4,4′-disubstituted azobenzenes of the polymerization of vinylacetate initiated by azoisobutyronitrile at 50°. The inhibitory effects of these substances can be attributed to their ability to engage in radical addition giving a less reactive hydrazyl type radical. The mechanism of the inhibition has been established by ESR and kinetic (stoichiometric) measurements. The value of k₅/k₂ (characteristic of the reactivity of an inhibitor) was determined for 9 substituents. The radical reactivity of the aromatic azo group was decreased by electron donor substituents and increased by electron acceptors. The substituent effect can be well interpreted by the Hammett equation; the value of the reaction constant was ? = +0.53.     

Chemische Vitamin D<Subscript>3</Subscript>-Bestimmung in Lebertran

The different aspects of Vitamin D₃ determination and the data reported in the literature are discussed. The spectrophotometric determination of Vitamin D₃ in cod-liver oil is carried out after the alkaline saponification, extraction of unsaponified parts, precipitation of accompanying sterols and the column- and thin-layer chromatographic purification and separation of vitamin D₃ on 40 cm plates from other vitamins. The dyestuff α-naphtholbenzein is suited well as standard substance for the better location and identification of vitamin D₃ zone on the thin-layer plate. The results obtained from the chemical method were checked through the simultaneous biological determination.     

Mikronachweis der Salicylsäure als Silbersalicylat

Zusammenfassung Es wird eine Methode beschrieben, nach der die Salicylsäure über ihr Ammonsalz als Silbersalicylat in kleinsten Mengen nachgewiesen werden kann. Es bilden sich dabei monokline Prismen in Form von Rhomboiden, die durch die Kristallwinkel, die schiefe Auslöschung und deren Beziehung zum Kristallumriß als Silbersalicylat identifiziert werden können. Erfassungsgrenze: 0,4 Salicylsäure. Ferner wird das unter Umständen ebenfalls bei der Reaktion auftretende Silbersalz der Benzoesäure und seine Unterscheidung von Silbersalicylat auf optischem Wege besprochen. Die Reaktion gelingt auch mit Mikrosublimaten.

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Summary A method is described whereby minimal amounts of salicylic acid can be detected as silver salicylate, viâ the ammonium salt. Monoclinic prisms of the form of rhomboids are produced, which may be identified as silver salicylate from the crystal angles, the oblique extinction, and the relationship of these to the crystal outline. The limit of the method is 0,4 salicylic acid. The optical method for distinguishing between silver salicylate and silver benzoate, which is also formed in certain circumstances in the course of the reaction, is discussed. The reaction may be successfully applied to micro-sublimates.

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Résumé On décrit une méthode, qui permet de déceler des plus petites quantités de l'acide salicylique comme salicylate d'argent en préparant d'abord le salicylate d'ammonium. Des prismes monoclines, en forme rhombique, se forment d'abord, qui peuvent être identifiés comme salicylate d'argent par l'angle du cristal (Kristallwinkel), l'extinction oblique (schiefe Auslöschung) et les relations de ceux aux contoures du cristal (Kristallumriß). Limite d'identification: 0,4 d'acide salicylique. Ensuite on discute aussi la différence entre le salicylate d'argent et le benzoate d'argent, qui se forme parfois au cours de la réaction, d'un mode optique. — La réaction peut être appliquée aussi à des micro-sublimés.

     

Use of thenoyltrifluoroacetone for the determination of manganese by activation analysis

A new procedure for the substoichiometric extraction of bivalent manganese by thenoyltrifluoroacetone into ethyl acetate has been developed and used in activation analysis. The value of the extraction constant has been found to be 3.1 x 10(-6); the pH range in which the extraction can be performed is 7.8-9.2. The influence of oxalate, citrate, tartrate, fluoride and cyanide ions has been studied. A selective substoichiometric extraction of manganese in the presence of Zr, Hf, Nb, Th, Fe and Sc is possible at pH 8-8.5, tartrate and fluoride being used as masking agents. Copper and cobalt can be screened by ammonia and cyanide respectively. The method has been used for the determination of manganese in biological materials, potassium fluoride and zirconium.