Rapid micro combustion methods for the determination of elements in organic compounds

Summary Advantages of the rapid combustion process for the micro determination of carbon and hydrogen, sulphur, and halogen are discussed, and methods for their estimation are described which have been adopted for routine analysis.

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Zusammenfassung Die Vorteile eines raschen Verbrennungsvorganges für die Mikrobestimmung von Kohlenstoff, Wasserstoff, Schwefel und Halogen werden beschrieben. Methoden für deren quantitative Bestimmung, die sich besonders für Serienanalysen bewährt haben, werden mitgeteilt.

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Résumé On discute les avantages du procédé rapide de combustion pour le microdosage du carbone, de l'hydrogène, du soufre et des halogènes et l'on décrit les méthodes pour leur dosage qui ont été adaptées dans les analyses en série.

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With 5 Figures.     

The determination of urea and other nitrogen compounds in urine by the DIE method

The heat of reaction of hypobromite with the non-protein nitrogen compounds contained in urine is very high. This fact can be utilized for the determination of these compounds by the inverse DIE method. The DIE method also allows a separate determination of urea based on the specific action of the enzyme urease.

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Zusammenfassung Die Reaktionswärme von Hypobromit mit den im Urin enthaltenen nicht-Protein Stickstoffverbindungen ist sehr hoch. Dieser Umstand kann zur Bestimmung dieser Verbindungen durch die inverse DIE-Methode verwendet werden. Die DIE-Methode gestattet auch die separate Bestimmung von Karbamid aufgrund der spezifischen Wirkung des Enzyms Urease.

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By describing the abowe two determinations, we wished to present the applicability of the inexpensive Hungarian instruments for fast and simple determinations in the biochemical field.

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This paper completes the material of the Hungarian Symposium on Thermal Analysis.     

Submicro methods for the analysis of organic compounds : The determination of hydroxyl groups

Various procedures were examined for the determination of organic hydroxyl groups. Conventional acetylation methods could not be used on the submicro scale, but the spectrophotometric method based on esterification with 3,5-dinitrobenzoyl chloride followed by extraction of the ester and colour development with alkaline acetone proved reasonably satisfactory for aliphatic alcohols. Acidic hydroxyl groups e.g. in phenolic compounds, were titrated accurately with 0.01 M tetrabutylammonium hydroxide in benzene-methanol solution in a pyridine medium ; visual end-points or potentiometricend-points with glass-silver or glass-in-stream platinum electrode pairs were used depending on the strength of the acidic group. Some differentiating titrations were possible. A general submicro bromination method for phenols was not feasible.     

Submicro methods for the analysis of organic compounds : The determination of acetyl groups

Methods are described for the determination of O-acetyl and N-acetyl groups in 30–80-μg samples of organic compounds. The best general method involved hydrolysis with Wenzel sulphuric acid and distillation of the acetic acid formed, in a small apparatus of the wiesenberger type, followed by visual acid-base titration. The overall recovery was 99.1% and the average relative accuracy was ± 2.5% ; accuracy and precision were slightly less satisfactory for alkaline hydrolysis or hydrolysis with phosphoric acid.     

Submicro methods for analysis of organic compounds : The determination of thiol groups

Several methods are described for the determination of thiol groups in organic samples weighing only 50 μg. Iodimetric methods were not widely applicable but the mercurimetric method of fritz and palmer in which thio-Michler's ketone serves as indicator was readily scaled down and gave excellent results (error ± 0.5% absolute) for all compounds tested. Diphenylcarbazone was also tried as the indicator; the procedure was satisfactory for most materials, but some anomalous results were obtained.     

A new method for simultaneous determination of nitrogen,hydrogen and halogen in organic compounds

Summary A new method for the determination of nitrogen, hydrogen and halogen in organic compounds is described. It is based on flash combustion in a fast stream (100 ml/min) of an automatically generated gas mixture (CO₂+20% O₂). A sample placed in an aluminium capsule and mixed with about 20 mg of V₂O₅ is combusted in the presence of CO₃O₄ coated on porous silica. Rapid gravimetric methods for final determination of hydrogen and halogens and a volumetric method for nitrogen are used. The combustion process has been examined by a rapid photography technique, mass spectrometry and gas chromatography. From an extensive statistical analysis (about 300 analyses) of various compounds containing C, H, O, N, Br, Cl, I and S, the following precision is obtained:s _N=0.03–0.15%;s _H=0.09–0.14%;s=0.07–0.20% absolute. The automation of the final determination of nitrogen and hydrogen has been examined.

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Eine neue Methode zur gleichzeitigen Bestimmung von Stickstoff, Wasserstoff und Halogen in organischen Verbindungen

Zusammenfassung Eine neue Methode zur Bestimmung von Stickstoff, Wasserstoff und Halogen wird beschrieben. Sie beruht auf der Entflammungsmineralisation in einem schnell fließenden (100 cm³/min) automatisch erzeugten Gasgemisch (CO₂+20% O₂). Die Probe wird in einer Aluminiumkapsel mit etwa 20 mg V₂O₅ vermischt und in Gegenwart von CO₃O₄ auf porösem Siliziumdioxid verbrannt. Zur Endbestimmung von Wasserstoff und Halogenen wurden schnelle, gravimetrische Methoden angewandt (die Jodogravimetrie für Halogene), während der Stickstoff gasvolumetrisch erfaßt wird. Zur Überprüfung des Verbrennungsprozesses wurden die Photographie, die Massenspektrometrie und die Gaschromatographie eingesetzt. Statistische Auswertung der Analysenergebnisse (etwa 300 Analysen) für verschiedene C-, H-, O-, N-, Br-, Cl-, J- und S-haltige Verbindungen ergab die folgenden Standardabweichungen:s _N=0,03–0,15 %;s _H=0,09–0,14% unds _X= 0,07–0,20% absolut. Die Möglichkeiten einer Automatisierung der Bestimmungsverfahren von Stickstoff und Wasserstoff wurden geprüft.

     

Submicro methods for the analysis of organic compounds: The determination of sulphide and disulphide groups

Summary Bromination methods are described for determination of sulphide and disulphide groups in organic samples weighing onlyca. 50g. Direct titration with visual end-point indication is suitable in some cases, but a back-titration method is of more general application. The accuracy obtained is of the same order as on much larger scales of working.

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Zusammenfassung Bromierungsverfahren zur Bestimmung von Sulfid- und Disulfidgruppen in Einwaagen von nur etwa 50g organischer Substanz wurden beschrieben. In manchen Fällen eignet sich die direkte Titration mit visueller Endpunktbestimmung, aber die Rücktitration ist allgemeiner anwendbar. Die Genauigkeit ist von der gleichen Größenordnung wie bei wesentlich größeren Einwaagen.

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Résumé On décrit les méthodes de bromation pour le dosage des groupements sulfures et disulfures dans les échantillons organiques, sur environ 50g de prise d'essai. Le titrage avec indication visuelle du point équivalent convient dans certains cas, mais une méthode avec titrage en retour se montre d'une application plus générale. La précision que l'on obtient est du même ordre de grandeur que pour le travail à échelle beaucoup plus grande.

     

Rapid coulometric method for the Kjeldahl determination of nitrogen

A rapid coulometric method for the Kjeldahl determination of nitrogen is described. The samples are digested by means of the Tecator AB digestion system which permits forty samples to be digested at the same time. The digestion products are diluted to 75 ml and 1 ml is coulometrically titrated in 1-2 min: 20-30 determinations can be performed per hour. For substances containing nitrogen in the per cent range the relative standard deviations for eight different substances were 0.1-1%.     

Automatic apparatus for the determination of carbon and hydrogen in organic compounds

A microanalytical determination of carbon and hydrogen in organic compounds is achieved by an original technique of coulometric titration in a nonaqueous medium. The apparatus, designed for the purpose, wholly automatic and monitored by a computer, makes possible the analysis of 23 samples without any intervention from the operator. Each analysis takes about 10 min and the precision of the method results in relative standard deviations of about 0.1 and 1% for carbon and hydrogen, respectively.     

Rapid determination of nitrate nitrogen in soils

A simple but effective method for pretreatment of soil samples is suggested. The application of an electrodynamic vibrator or ultrasonic device eliminates the necessity for continuous stirring in direct potentiometric determination of nitrate nitrogen. It also makes the extraction process faster, and the apparatus could easily be used in automatic systems for continuous soil control.     

Rapid and quantitative pentafluorobenzoylation of nitrophenols and other phenolic compounds in water for gas-chromatographic determination with electron capture detection

Summary Derivatization of nitrophenols in water with pentafluorobenzoylchloride for a gas-chromatographic determination with electron capture detection is achieved by phase transfer reaction using dicyclohexyl-18-crown-6 as catalyst.

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Schnelle und quantitative Pentafluorobenzoylierung von Nitrophenolen und anderen Phenolen im Wasser für ihre gas-chromatographische Bestimmung mit Elektroneneinfangdetektion

     

Rapid titrimetric methods for the determination of vanadium and molybdenum in mixtures

Summary A rapid and accurate method has been developed for the volumetric determination of molybdenum(VI) and vanadium(V) in mixtures, using cerium(IV) sulphate. In this procedure the sample solution is reduced in a mercury reductor (to give Mo^V and V^IV) and an aliquot of the reduced solution is titrated with Ce^IV solution using either ferroin, N-phenyl anthranilic acid, or barium diphenylamine sulphate as indicator. This titration gives the amount of molybdenum present, as V^IV does not interfere under the conditions applied. Another aliquot of the reduced solution is titrated with Ce^IV solution and rhodamine 6 G as indicator (observing the quenching of the fluorescence). This titration corresponds to the sum of molybdenum and vanadium. The vanadium content can be calculated by difference.

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Zusammenfassung Zur schnellen und genauen volumetrischen Bestimmung von Molybdän(VI) und Vanadium(V) in Mischungen wird Cer(IV)-sulfat als Reagens verwendet. Die Probelösung wird im Quecksilberreduktor reduziert (wobei Mo^V und V^IV gebildet werden) und ein aliquoter Teil der reduzierten Lösung wird mit Ce^IV-Lösung titriert, wobei Ferroin, N-Phenylanthranilsäure oder Bariumdiphenylaminsulfonat als Indicator dient. Aus dieser Titration erhält man den Molybdängehalt, da V^IV unter den angewendeten Bedingungen nicht stört. Ein weiterer Teil der reduzierten Lösung wird mit Ce^IV-Lösung gegen Rhodamin 6 G titriert (Endpunkt durch Fluorescenzlöschung), woraus man die Summe Mo + V erhält. Der Vanadiumgehalt ergibt sich aus der Differenz.

     

Comparison of two electrodes for the determination of ammonia and nitrogen compounds

Summary Two types of electrodes for the determination of ammonia are compared: one of the liquid membrane and one of the gas detecting type. Important electrode characteristics as response time, sensitivity and selectivity are commented. The ammonia electrode was tested in practice by analysis of ammonia and nitrate in canal water. The precision of the methods described was tested by analysis of synthetic samples, and by comparison with a volumetric and colorimetric method.

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Vergleich zweier Elektroden für die Bestimmung von Ammoniak und von Stickstoffverbindungen

Zusammenfassung Zwei Elektrodentypen (Flüssig-Membran und Gasdetektor) für die Ammoniakbestimmung wurden einem Vergleich unterzogen. Wichtige Charakteristiken (Ansprechzeit, Empfindlichkeit und Selektivität) werden diskutiert. Die praktische Prüfung erfolgte an Hand der Bestimmung von Ammoniak und Nitrat in Kanalwasser. Die Präzision wurde mit synthetischen Proben getestet sowie durch Vergleich mit einer volumetrischen und einer colorimetrischen Methode.

     

Submicro determination of hydrogen in organic compounds: Application to the determination of water and simultaneous determination of nitrogen

The calcium hydride reaction with water is used as a basis for determining hydrogen. The liberated hydrogen is collected and measured in a gasometer. Representative organic compounds containing only CHO, mixed with a catalyst, are combusted in a porcelain boat in an atmosphere of pure, dry carbon dioxide. Hydrogen is collected over 50% KOH, as in the Pregl-Dumas method for nitrogen, the volume of gas is corrected for T and P and the percentage of hydrogen is calculated. The hydrogen gas occupies 14 times the volume of nitrogen thus permitting use of the micro quantities.     

Electrochemical methods for the determination of total arsenic and arsenic compounds

The determination of total arsenic and of arsenic compounds in biological and inorganic samples is a task frequently encountered by analysts. Several elecrochemical methods have been developed for the determination of total arsenic (generally after mineralization of the sample), arsenite, arsenate, methylarsonic acid and dimethylarsinic acid. The electrochemical behavior of several other organic arsenic compounds was also studied. This paper reviews these electrochemical methods, their application to environmental samples, and the problems encountered in the electrochemical determination of arsenic and arsenic compounds.     

Profiling methods for the determination of phenolic compounds in foods and dietary supplements

Profiling methods are needed that separate and detect all the phenolic compounds in a single extract of a food material. These methods must be comprehensive, rapid, and rich in spectral information. Fourteen methods that meet, or have the potential to meet, these criteria have been selected from the recent literature for review. In general, the methods employ a single aqueous methanol extraction, separation on a reversed-phase C column, and detection by UV/vis spectroscopy and mass spectrometry. The variations in extraction, separation, and detection are discussed. An increasingly important aspect of these methods is the archiving of data to permit cross-comparison of samples and standards and retrospective analysis. This review shows that the necessary technology is available to achieve the desired analytical goals.