Microdetermination of tellurium and organo-tellurium compounds

Summary A method is described to convert elemental tellurium and organotellurium compounds quantitatively to Te(IV) by digestion with a mixture of nitric and sulfuric acids in the micro-Kjeldahl flask. After removal of nitrogen oxides by means of urea, exactly 5 ml of 0.02N potassium dichromate is added, whereupon Te(IV) is oxidized to Te(VI). The tellurium content of the sample is related to the amount of dichromate consumed, the latter being determined either spectrophotometrically or by back-titration with 0.02N ferrous sulfate. This method, applicable to 1–4 mg of tellurium, is amenable to automation and multi-element determinations.

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Zusammenfassung Ein Verfahren zur quantitativen Überführung von elementarem und organisch gebundenem Tellur in Te(IV) durch Mineralisierung mit einem Gemisch von Salpetersäure und Schwefelsäure im Mikro-Kjeldahl-Kölbchen wurde beschrieben. Nach Entfernung der Stickoxide mit Harnstoff werden genau 5 ml 0,02-n Kaliumbichromat zugesetzt, wodurch Te(IV) zu Te(VI) oxydiert wird. Der Tellurgehalt der Probe ergibt sich aus der Menge verbrauchten Bichromats, die entweder spektrophotometrisch oder durch Rücktitration mit 0,02-n Eisen(II)-sulfat bestimmt wird. Dieses auf 1 bis 4 mg Te anwendbare Verfahren ist automatisierbar und bei gleichzeitiger Bestimmung mehrerer Elemente anwendbar.

     

Determination of selenium and tellurium in organic compounds and organic materials — A review

Summary A review is given of methods available for determination of selenium and tellurium in organic compounds and organic materials. The various techniques for decomposition (wet digestion, combustion and bomb fusion) are covered, and the investigational work on decomposition methods is mentioned. The various types of reactions which have been used as methods of finish are also discussed. Methods which involve only physical measurements are not included.

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Zusammenfassung Eine Übersicht über verfügbare Methoden zur Bestimmung von Selen und Tellur in organischen Verbindungen und Materialien wurde gegeben. Die verschiedenen Verfahren zur Zerstörung (nasse Veraschung, Verbrennung und Bombenaufschluß) wurden berücksichtigt und die über Zerstörungsmethoden vorliegenden Publikationen angeführt. Die für die Endbestimmung verwendeten Reaktionstypen wurden erörtert. Physikalische Meßmethoden wurden nicht eingeschlossen.

     

Oeganic compounds of selenium and tellurium

2,3-Disubstituted 2,3-dihydrobenzo[b]selenophenes were obtained in the form of trans isomers by the action of selenium tetrabromide on dibenzal- and benzalacetone in benzene.See [1] for communication I.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1340–1342, October, 1977.     

Organic compounds of selenium and tellurium

Heterocyclic compounds containing a selenium (IV) atom as the heteroatom were obtained by the action of selenium tetrahalides on 1,5 and 1,6-diolefins and their derivatives.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 58–62, January, 1977.     

Microdetermination of calcium in organic compounds

A sensitive method for microdetermination of calcium in organic compounds is described. The combustion in an oxygen stream or oxygen flask with electrical ignition of the sample in porcelain crucible was found advisable. Carbon dioxide has to be expelled and the erroneous effect of phosphate eliminated by adsorption on an anion exchanger prior to the spectrophotometric determination of calcium with glyoxal bis (2-hydroxyanil).     

Microdetermination of halogens in organic compounds

Summary Safford andStragand have described a method for the microdetermination of halogens using a silver-gauze-absorbent. The procedure is very simple, but unfortunately the results are not precise enough to enable the method to be recommended.The method has been modified. The sample is burned in an atmosphere of oxygen using a platinum catalyst, and the halogen formed is quantitatively absorbed on electrolytic silver wool in a special absorption-funnel, which is then weighed. The method is precise and accurate (standard deviation of the results: 0.12 per cent). Silver wool presents a much greater surface than silver-gauze and absorbs on an average 160 mg of chlorine per gram, i. e. forty or fifty times as much as a piece of silvergauze of the same dimensions. The charge in an absorption-funnel therefore has a long life for routine analysis of halogen compounds. The operating temperature range of the silver-wool is wide, so that precise control is not neccessary. The method compares favourably in accuracy, precision and simplicity with established methods.

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Zusammenfassung Safford undStragand veröffentlichten eine Methode zur Mikro-Halogenbestimmung mit Hilfe eines Silberdrahtnetzes als Absorptionsmittel. Dieses Verfahren ist sehr einfach, aber seine Resultate leider nicht genau genug, um es zu empfehlen. Die Methode wurde daher modifiziert. Die Substanz wird in einer Sauerstoff-Atmosphäre über einem Platinkontakt verbrannt, das Halogen quantitativ in einem besonderen Absorptionsröhrchen über elektrolytischer Silberwolle absorbiert und dann gewogen. Diese Methode ist genau und verläßlich (mittlere Abweichung der Resultate: 0,12%). Silberwolle bietet eine viel größere Oberfläche als Silberdrahtgeflecht und absorbiert durchschnittlich 160 mg Chlor pro Gramm, das heißt 40- bis 50mal mehr als Silberdrahtgeflecht gleichen Ausmaßes. Die Füllung eines Absorptionsr öhrchens reicht daher für viele Serienanalysen von Halogenverbindungen. Das geeignete Temperaturbereich für Silberwolle ist groß, eine genaue Kontrolle daher nicht nötig. Die Genauigkeit und Einfachheit der Methode ist auch im Vergleich mit bekannten Analysenverfahren durchaus zufriedenstellend.

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Résumé Safford etStragand ont décrit une méthode de microdosage des halogènes par fixation sur toile d'argent. La technique en est très simple mais elle ne permet pas d'obtenir des résultats de précision suffisante. Elle a été modifiée par les auteurs.La prise d'essai est brûlée en atmosphère d'oxygène en présence d'un catalyseur de platine et les halogènes formés sont quantitativement fixés sur de la laine d'argent électrolytique dans un tube d'absorption spécial qui est ensuite pesé. La méthode est précise et exacte (l'écart type des résultats est égal à 0,12 pour cent). La laine d'argent présente une surface beaucoup plus élevée que la toile d'argent et fixe en moyenne environ 160 mg de chlore par gramme, soit, pour le même encombrement, quarante à cinquante fois plus que la toile d'argent. Il en résulte une longue durée de la charge du tube d'absorption lors d'analyses en série des composés halogénés. La température de la laine d'argent peut varier dans un large domaine de sorte qu'il n'est pas nécessaire d'en assurer une régulation précise. La méthode se compare favorablement aux méthodes classiques quant à son exactitude, sa précision et sa simplicité.

     

The simultaneous microdetermination of carbon,hydrogen, arsenic,or selenium in organic compounds

Simple modifications have been described for the simultaneous microdetermination of carbon, hydrogen, and arsenic or selenium in organic compounds using the rapid straight empty tube combustion technique. A silica insertion tube placed in the combustion tube at the open end of the ignition capsule and cooled via external exposure of the combustion tube around it to a stream of air, was found to be suitable for the quantitative retention of arsenic trioxide produced during the combustion of organo-arsenic compounds. The same modification was proved to be suitable for complete trapping of selenium dioxide produced in the combustion of organo-selenium compounds. In the latter case, the insertion tube was packed at one end with a short silica wool plug and cooling it with air is unnecessary.Using these simple modifications, accurate and reproducible carbon, hydrogen, and arsenic or selenium results were obtained in the analysis of a wide range of organic compounds containing arsenic or selenium. The conventional gravimetric finish was employed for the evaluation of three elements.     

Microdetermination of nitro groups in organic compounds

Summary A simple procedure for microdetermination of nitro groups in organic compounds is described. It is based on reduction with palladium-on-carbon catalyst in acetic acid in a modified Roth apparatus.

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Zusammenfassung Ein einfaches Verfahren zur Mikrobestimmung von Nitrogruppen in organischen Verbindungen wurde beschrieben. Es beruht auf der Reduktion in Essigsäure mit Palladium-Kohle als Katalysator in einem modifizierten Apparat nachRoth.

     

Differential pulse polarographic determination of arsenic, selenium and tellurium at mug levels

An analytical method, based on differential pulse polarography, for determination of arsenic, selenium and tellurium in solid matrices, is described. The method involves decomposition of the matrix with a mixture of nitric, perchloric and hydrofluoric acid, isolation of tellurium from the other analytes by liquid-liquid extraction (from 4M hydrochloric acid with methyl isobutyl ketone), and determination of the analytes. Tellurium is determined separately, and arsenic is determined in the same solution as selenium after determination and oxidation of the selenium and addition of catechol. Graphitized carbon black and chelating resin were used to eliminate the organic solvent in the aqueous solution and avoid interferences due to the other metals of the matrix. The decomposition, the influence of each analyte on the determination of the others, and the extraction process were given particular attention. The method is characterized by>96% recovery, with a relative standard deviation ranging from 2 to 10% at ppm levels.     

Microdetermination of the azide group in organic compounds

A simple, rapid and accurate micro-method for the analysis of mono- and diazide organic compounds is described. It is based on the Curtius rearrangement reaction. Glacial acetic acid is found to be the best decomposition medium. The acyl azide function yields two nitrogen atoms per azide group, but the diazides investigated ultimately give five nitrogen atoms per group on oxidation of their decomposition products, with acidified cerium(IV) sulphate solution. The decomposition time varies from 10 min for monoazides to 20 min for diazides. Accurate results were obtained for a representative series of 18 mono-and diazides.     

Microdetermination of the azo group in organic compounds

Summary Simple micromethods are described for the determination of the azo group in organic compounds by reduction with iron(II) in acidic and alkaline media. Four equivalents of iron(III) are produced per mole of the azo function and are titrated with titanium(III) using ammonium thiocyanate as indicator. A gasometric method is also described which is based on reduction of the compounds into the amines by zinc powder and hydrochloric acid, followed by de-amination reaction with nitric acid whereby two moles of nitrous oxide gas is liberated per mole of the azo function.

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Zusammenfassung Einfache Mikromethoden für die Bestimmung der Azogruppe in organischen Verbindungen durch Reaktion mit Eisen (II) in saurem und alkalischem Medium wurden angegeben. Für ein Mol Azofunktion werden 4 Äquivalente Fe(III) gebildet und mit Titan(III) gegen Ammoniumthiocyanat als Indikator titriert. Ein gasometrisches Verfahren beruht auf der Reduktion zu Aminen mittels Zinkpulver und Salzsäure und nachfolgender Desaminierung mit Salpetersäure, wobei 2 Mole N₂O pro Mol Azofunktion freigesetzt werden.

     

Fluorine-induced chemiluminescence detection of biologically methylated tellurium,selenium, and sulfur compounds

Summary The sensitive detection of volatile, methylated selenium and tellurium compounds based on capillary gas chromatography coupled to fluorine-induced chemiluminescence detection is described. The method requires no sample derivatization, and the detection limits for selenides and tellurides (low pg range) are the lowest reported to date. This technique can resolve and speciate complex mixtures of methylated tellurium, selenium, and sulfur gases and is useful for analysis of selenium and tellurium gases in environmental samples that also contain usually interfering reduced sulfur gases. Applications of the technique for analysis of bacterial and fungal headspace samples are presented.     

Activation analysis for selenium and tellurium trace impurities in gallium, arsenic and gallium arsenide

Destructive and non-destructive activation analysis for selenium and tellurium has been studied. In destructive analysis the selenium and tellurium activities are co-extracted from the irradiated and dissolved matrix elements with dithizone/CCl(4), reagent in a hot-chamber by remote manipulation, then separated from each other by diethylammonium-N,N-diethyldithiocarbamate/CCl(4) extraction, tellurium going into the organic phase and selenium being retained by the aqueous phase. The sensitivity of the method is 10(-8)g for both elements. By non-destructive methods, selenium can be determined down to 10(-6)g on short irradiation, and down to 3 x 10(-8) g on long irradiation and cooling, and tellurium down to 10(-6) g with long irradiation and cooling.     

Microdetermination of fluorine in organic compounds containing phosphorus and in hexafluorophosphates

Summary A method for the microdetermination of fluorine in organic compounds containing phosphorus is described. After combustion in a Vycor flask, the species containing phosphorus are oxidized to orthophosphate with alkaline hypobromite. Phosphate is adsorbed on zinc oxide which need not be removed prior to titration of the fluoride. Fluoride is titrated potentiometrically with 0.02M lanthanum(III) in 50% ethanol solution at p_H 5–7. A fluoride ion-specific indicator electrode and a calomel reference electrode are used in conjunction with an expanded-scale p_H meter to monitor the emf. This method can also be used for the determination of total fluorine in inorganic hexafluorophosphates. For the more stable compounds such as potassium hexafluorophosphate, a combustion aid (paraffin) must be added to promote combustion.

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Zusammenfassung Ein Verfahren zur Mikrobestimmung von Fluor in organischen, phosphorhältigen Verbindungen wurde beschrieben. Nach der Verbrennung in sauerstoffgefüllten Kolben werden die phosphorhältigen Produkte mit Alkalihypobromit zu Orthophosphat oxydiert. Dieses wird an Zinkoxid adsorbiert, das vor der Fluoridtitration nicht entfernt werden muß. Die Titration erfolgt potentiometrisch mit 0,02-m Lanthan(III)-lösung in 50%igem Äthanol bei p_H 5–7. Eine fluoridspezifische Indikatorelektrode und eine Kalomel-Bezugselektrode werden in Verbindung mit einem p_H-Meter mit gedehnter Skala zur Messung verwendet.Das Verfahren ist auch zur Fluorbestimmung in anorganischen Hexafluorphosphaten geeignet. Für die Analyse beständiger Verbindungen wie z. B. Kaliumhexafluorophosphat verwendet man Paraffin als Verbrennungszusatz.

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Work performed under the auspices of the U. S. Atomic Energy Commission.     

Determination of arsenic in organic compounds

Summary Methods are described for the determination of arsenic in organic compounds. Following oxygen flask combustion using a nichrome gauze arsenic is estimated either by titration of arsenic(III) with iodine or by titration of iodine liberated from iodide by arsenic(V). An alternative colorimetric procedure involving measuring the absorbance of molybdenum blue is used following open tube digestion in the absence of halogens or sealed tube digestion in the presence of halogens.

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Bestimmung von Arsen in organischen Verbindungen

Zusammenfassung Nach Verbrennung im Sauerstoffkolben mit einem Nickeldrahtnetz als Katalysator wird das Arsen entweder durch. Titration des As(III) mit Jod oder durch Titration des durch As(V) aus Jodid ausgeschiedenen Jods bestimmt. Ein anderes Verfahren beruht auf der kolorimetrischen Bestimmung von Methylenblau nach Verbrennung im offenen Rohr bei Abwesenheit von Halogenen oder im verschlossenen Rohr bei Anwesenheit von Halogenen.

     

Therapeutic potential of selenium and tellurium compounds: opportunities yet unrealised

Despite being disparaged for their malodorous and toxic demeanour, compounds of selenium, a bio-essential element, and tellurium, offer possibilities as therapeutic agents. Herein, their potential use as drugs, for example, as anti-viral, anti-microbial, anti-inflammatory agents, etc., will be surveyed along with a summary of the established biological functions of selenium. The natural biological functions of tellurium remain to be discovered.     

Microdetermination of oxygen at traces level in organic sulfur compounds

We have described an original method allowing us to determine traces of oxygen in organic compounds such as polymers modified through grafting of functions containing oxygen.The method allows us to obtain oxygen contents included between a few hundred ppm and 7 to 8%. It consists in the pyrolysis of the sample, the reduction of oxygen to carbon monoxide and, finally the detection of the latter in an infrared analyzer.