Multiple determinations in the micro Dumas nitrogen method

Summary A multiple analysis method for the Dumas nitrogen determination has been described. The furnace is provided with eight combustion tubes arranged in a circle around the axis of the furnace. An improved nozzle-type nitrometer, without ground joints, has been designed. The multiple determinations are simultaneously carried out as in usual method, permitting thirty two analyses in a 7-hour working day. The standard deviation-error of estimate from 88 analyses in routine work is ±0.12% N.

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Zusammenfassung Ein Verfahren zur gleichzeitigen Durchführung mehrerer Stickstoffbestimmungen nachDumas wurde beschrieben. Der Verbrennungsofen kann acht Verbrennungsrohre in gleichmäßiger Entfernung von seiner Längsachse aufnehmen. Ein verbessertes Düsenazotometer ohne Schliffverbindungen wurde konstruiert. Die Analysen werden gleichzeitig in der üblichen Art durchgeführt, so daß im 7stündigen Arbeitstag 32 Bestimmungen möglich sind. Die mittlere Abweichung von 88 Analysen im Routinebetrieb betrug ± 0,12% N.

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Résumé On a décrit une méthode d'analyse multiple pour le dosage de l'azote selonDumas. Le four est muni de huit tubes á combustion disposés suivant un cercle autour de l'axe du four. On a construit un nitromètre perfectionné de type à étranglement, sans joints rodés. On effectue simultanément les dosages multiples comme dans la méthode habituelle, ce qui permet de réaliser trente deux analyses en une journée de travail de 7 heures. L'écart type calculé à partir de 88 analyses dans un travail en série est de ±0,12% N.

     

Optimization of a nitrogen analyser based on the Dumas method

The objectives of this work was to obtain a total nitrogen concentration in milk with the Dumas method for industrial and research applications. This method was faster than the Kjheldal method (5 min against 2 h or 3 h) but less precise. A three factor experimental design was performed to optimize the instrument, a FP-2000 supplied by LECO. The first interpretation of the experimental design was disappointing and no conclusion could be done. It was not a failure of experimental design but a lack of thinking on the physical and chemical aspect of the problem. Selection and construction of composite responses based on chemical and physical consideration were the keys to optimize the Dumas method. This method is now as precise as the Kjheldal method, but considerably faster.     

On the Dumas determination of nitrogen

Summary Reactions in theDumas nitrogen determination method have been investigated. The presence of free oxygen in the combustion tube was found to cause retention of nitrogen oxides by the metal oxide catalyst. Nickel oxide was found superior to copper oxide because it allows the use of higher temperatures and does not liberate oxygen on heating, thus eliminating the retention error.A new method is described which uses automatic combustion and makes use of the reaction C + CO₂ = 2 CO at 1050° C and combustion with nickel oxide at 1000° C. The standard deviation of 20 analyses on known compounds carried out in direct succession was 0.045%.

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Zusammenfassung Einige bei der Stickstoffbestimmung nachDumas ablaufende Reaktionen wurden untersucht. Es wurde gefunden, daß die Gegenwart von freiem Sauerstoff im Verbrennungsrohr zu einer chemischen Bindung von Stickstoffoxyden an den Metalloxydkatalysator führt. Nickeloxyd eignet sich besser als Kupferoxyd, da es die Anwendung höherer Temperaturen ermöglicht und beim Erhitzen keinen Sauerstoff abgibt, so daß der obenerwähnte Fehler vermieden wird.Eine neue Methode wird beschrieben, nach der die Substanz durch Anwendung der Reaktion C + CO₂ = 2 CO bei 1050° C vergast und dann über Nickeloxyd bei 1000°C verbrannt wird. Die mittlere Abweichung bei 20 direkt nacheinander ausgeführten Analysen betrug 0,045%.

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Résumé On a examiné les réactions qui se produisent dans le dosage de l'azote par le procédéDumas. On a trouvé que la présence d'oxygène libre dans le tube à combustion produisait une rétention des oxydes de l'azote par l'oxyde métallique catalyseur. L'oxyde de nickel a été trouvé supérieur à celui de cuivre car il permet l'emploi de plus hautes températures et ne libère pas d'oxygène par chauffage, ce qui élimine l'erreur de rétention.On décrit une nouvelle méthode qui utilise la combustion automatique et fait usage de la réaction C + CO₂ = 2 CO à 1050° C et de la combustion avec l'oxyde de nickel à 1000° C. L'erreur standard sur 20 analyses de composition connue effectuées à la suite a été de 0,045%.

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With 7 figures.     

Dumas nitrogen determination with decimilligram samples

Summary A small-sizeDumas nitrometer of 0.2-ml capacity, graduated in microliters, and permitting estimation of tenths of microliters, has been described. The 0.4-mg samples are weighed on the Garner quartz fiber balance. The standard error of estimate from 10 serial analyses with 0.4-mg samples of azobenzene was computed equal to ±0.28% N. For 0.1-mg samples the corresponding figure is ±0.96% N, but it should be possible to improve this value.

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Zusammenfassung Ein Azotometer wird beschrieben, dessen Meßrohr in Mikroliter geteilt ist und einen Gesamtinhalt von 0,2 ml hat. Zehntel-Mikroliter können geschätzt werden. Einwaagen von 0,4 mg Substanz werden mit der Garner Mikrowaage vorgenommen. Der mittlere Fehler einer Einzelbestimmung wurde aus den Ergebnissen von zehn Azobenzol-Analysen zu ±0,28% Stickstoffermittelt. Die entsprechende Zahl für 0,1-mg-Proben, ±0,96% Stickstoff, dürfte einer Verbesserung zugänglich sein.

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Résumé On décrit un petit nitromètreDumas de 0,2 ml de capacité, gradué en microlitres et permettant l'estimation de dixièmes de microlitres. Les échantillons de 0,4 mg sont pesés sur la microbalance à fil de quartz de Garner. L'erreur standard déterminée sur 10 analyses en série avec des prises de 0,4 mg d'azobenzène est estimée à ±0,28% N. Pour des prises d'essai de 0,1 mg le chiffre correspondant est ±0,96 N, niais il doit être possible d'améliorer cette valeur.

     

Microdetermination of molybdenum by an automatic reaction-rate method

An automatic reaction-rate method is described for the microdetermination of molybdenum; the method is based on the hydrogen peroxide-iodide reaction which is catalyzed by molybdenum. The effect of reagent concentrations was studied and the maximum tolerable amounts of interfering ions were determined. Procedures for the determination of 0.01–0.15 μg and 0.1–1.0 μg molybdenum per milliliter are given ; 0.036–2.5 μg of molybdenum could be determined with relative errors of about 2%.     

Microdetermination of the keto group by the oxime method

Summary A method was developed for microdetermination of the carbonyl group in ketones, esters of keto acids and also in diketones, capable of giving dioximes, by oximation of them with hydroxylamine hydrochloride in the presence of triethanolamine.     

Microdetermination of nitrogen with a modified pyrolysis-chemiluminescence system

Summary In order to develop a versatile method for microanalysis of chemically bound nitrogen, several parts of the Antek Nitrogen Detector system have been modified. These modifications have resulted in a fourfold increase in impulse rate and a linear calibration curve over four decades of concentration. Chemically bound nitrogen can be measured directly in 0.5–10 mg or 1–10l samples from 0.5ppm up to about 3% N if appropriate operating parameters are chosen. Analyses of different types of nitrogen compounds have yielded significantly better recoveries than the Kjeldahl method, except for azo compounds. The method has been tested with various substances and proved superior to the Kjeldahl method in handling and efficiency, with acceptable results.

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Stickstoff-Mikroanalyse mit einem modifizierten Pyrolyse-Chemilumineszenz-System

Zusammenfassung Durch Änderungen im Verbrennungsteil und bei der Gasführung wurde beim Antek-Stickstoff-Detektor eine deutliche Steigerung der Impulsausbeute und ein erweiterter Linearitätsbereich der Eichkurven erreicht. Mit 0,5 bis 10 mg bzw. 1 bis 10l Probemenge lassen sich Gehalte an chemisch gebundenem Stickstoff von 0,5 ppm bis ca. 3% bestimmen. Die Intensivverbrennung bewirkt weitgehende Unabhängigkeit von der N-Bindungsart mit Einschränkungen bei Azo- und Hydrazo-Verbindungen. Vergleichende Mikro- und Spurenanalysen verschiedener chemischer und technischer Produkte belegen die Leistungsfähigkeit und die Vorteile des modifizierten Pyro-Chemilumineszenz-Reaktors gegenüber der Kjeldahl-Methode.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

Determination of nitrogen and carbon in refractory nitrides and carbonitrides by means of Dumas gas chromatography

The applicability of an automated Dumas-GC method for the determination of nitrogen and carbon in refractory materials was investigated. Analyses were carried out to determine nitrogen and carbon in TiN, ZrN and Ti(C,N) using CuO, V₂O₅ and Pb₃O₄ as oxidizing additives. The reproducibility of the analyses obtained with V₂O₅ was better than ± 1 rel% for major constituents. An estimation of the accuracy of the Dumas-GC method shows that this rapid and low-cost method can compete with other methods, at least for the refractory nitrides and carbonitrides of the transition metals.     

Microdetermination of dissolved oxygen in water by a rapid spectrophotometric method

A spectrophotometric method utilizing the dye indigo carmine has been applied to the analysis of dissolved oxygen in water samples. Oxygen concentration has been determined by the decrease in absorbance at 410 mμ of reduced indigo carmine solutions oxidized by dissolved oxygen. A simple modification of the sample compartment of a Bausch and Lomb Spectronic 20 or 340 spectrophotometer allows rapid and accurate measurements to be made within 3 min. Dissolved oxygen in the ranges of 0 to 10% and 0 to 100% saturation can be analyzed without many of the interferences inherent in the standard Winkler method.     

Repeatability and reproducibility of determination of the nitrogen content of fishmeal by the combustion (Dumas) method and comparison with the Kjeldahl method: interlaboratory study

Ten fishmeal samples (hidden duplicates of 4 meals plus 2 high-protein meals as a Youden pair), tryptophan, and nicotinic acid were analyzed by 18 laboratories using the Dumas method. Thirteen of the laboratories also analyzed the same 12 samples using their current Kjeldahl method. Recoveries (+/-SR) of tryptophan and nicotinic acid were 99.3+/-1.04 and 98.8+/-2.11% by Dumas and 97.1+/-3.03 and 74.6+/-26.76% by Kjeldahl. The Dumas method gave significantly greater values (P < 0.001) than the Kjeldahl method. For fishmeals, Kjeldahl N = 0.989 of Dumas N (P < 0.001). A similar proportionate difference (0.984 of Dumas N) was observed with tryptophan. Most laboratories failed to determine nicotinic acid correctly by Kjeldahl. For fishmeals, the relative standard deviations for repeatability and reproducibility were for Dumas 1.48 and 2.01% and Kjeldahl 1.62 and 2.37%, respectively. A single analysis conducted in 2 laboratories should not differ by more than 5.63% of the mean value when measured by Dumas or by more than 6.64% by Kjeldahl. It is concluded that with fishmeal, Dumas gives a more reliable measure of organic nitrogen than Kjeldahl, and, therefore, Dumas should be the method of choice.