Combustion tube method

Germanium in organometallic compounds can be determined by a modification of the combustion tube method. The sample is mixed with a large excess of chromic oxide, the organic elements are burnt in the tube and are absorbed downstream, whereas the... 

The combustion may be carried out in two ways (a) in a tube sealed at one end, the C02 being generated from materials inside the tube, and (6) in a tube open at both ends, the C02 being generated in a second vessel or in a Kipp s apparatus of the Pregl type and passed into the combustion tube. Method (a) is the more convenient when estimations are conducted occasionally, and method (b) when estimations are frequently conducted. 

Kendall, C. E. Grim, 1990. Combustion tube method for measurement of nitrogen isotope ratios using calcium oxide for total removal of carbon dioxide and water. Anal. Chem. 62 526-529. 

Quartz Tube Method the sample is burned in a quartz tube and a stream of purified air carries the combustion gases into a hydrogen peroxide solution. 

Estimatiofi of Niiroo-ot, Second Method.—Another method w hich dispenses with the small furnace and bicarbonate tube may also be used. The long combustion tube is closed at one end and magnesite m small lumps is introduced into the tube and shaken down to the closed end until there is a layer of about 13- 15 cm. (5—6 in.). This is kept in place by a plug of asbestos and the tube is filled s-uccessively with 5 cm. (2 in.) of coarse copper o.xide, then fine copper oxide mixed with the substance, a further layer of coarse copper oxide, and finally the... 

The dry combustion-direct injection technique provides many advantages over other methods, such as quick response and complete oxidation for determining the carbon content of water. Its primary shortcoming is the need for rapid discrete sample injection into a high-temperature combustion tube. When an aqueous sample is injected into the furnace, it is instantaneously vapourised at 900 °C and a 5000-fold volume increase can be expected. Such a sudden change in volume causes so-called system blank and limits the maximum volume of injectable water sample, which in turn limits the sensitivity [106,107]. 

For analyses, an 0.5 g sample is weighed into a porcelain boat and inserted into the combustion tube with an oxygen flow of —30 cc/min. With a cold trap in place, the sample is ignited by heating the combustion tube with a meker burner. The coal sample is allowed to burn freely, and then the temperature is raised to the burner maximum for 5 min. The combustion tube is cooled for 5 min and separated from the condenser section. The condenser is removed from the cold trap and allowed to warm to ambient temperature. Add 10 ml of water to the condenser and flush into a 50 ml volumetric flask. Make to volume with water and mix. Take an aliquot of 15 ml or less containing up to 0.3 fxg of selenium and proceed as in the hydride method for arsenic, tin, and bismuth by AAS, as previously described. 

Carbon Analytical Procedures. When total carbon in nitrogen contg compds or compds (such as expls or propints) is detd by combustion in a glass tube contg CuO (method of Dumas), there is always the possibility that oxidation of C to C02 will accelerate to such an extent that the sample will expl or defgr (thus destroying the combustion tube) even when the sample is previously mixed with materials retarding combustion such as benzophenone proposed by Jovinet et al, (Ref 8). Modifications of method of Dumas proposed by Boivin (Ref 6) or by Courtecuisse (Ref 9) are not always applicable to expls or proplnts... 

A simple method for the determination of C and H is that of Roger and McKay (loc. cit.). Amounts of substance from 20—40 mgs. are used and the heating mortar of the Pregl method is dispensed with and simple fillings of the macro type are used in the combustion tube. 

Method (a).—500 gms. of wire-form and 100 gms. of powder CuO are placed in separate fireclay basins. The first is heated to a dull red heat in a muffle furnace, and the second over a Bunsen flame. While they are being heated the combustion tube is prepared. 

Method (b).—The combustion tube is in every way similar to that used in connection with the estimation of C and EL... 

In effecting the rednetion of oxygen compounds by this method, zinc dnst is mixed with the snbstance to be reduced, a.ud the mixtnre is then heated in a combustion tube. The rednetion is often facilitated by passing a stream of hydrogen or carbon dioxide through tho heated mixture ... 

See discussion of analytical methods in Bygd6n, Silicium als Vertreter des Kohlenstoffs organischer Verbindungen, p. 71 (Almqvist and Wiksells Boktryckeri -A.-B. Upsala, 1916). The combustion tube preferably is packed with platinized asbestos and rolled platinum gauze. 

This method has given results of acceptable reproducibility with a wide variety of organosiloxane polymers, although each type of polymer has its optimum temperature of oxidation in the combustion tube. In general, the oxidation temperatures for polymers with... 

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