Carbon dioxide, conductometric determination

Ogneva et al. (28) use essentially the same method sample weight of 0.5 g, oxygen stream, 1250°C, coulometric production of reagents. The procedure described by Arsenijevic and Tomasevic (29) is similar too. For the combustion of 0.1 to 1 g titanium an iron and copper flux is used, for the analysis of zirconium 1 g iron and 0.5 g tin are used. The combustion temperature is 1000°C. Carbon dioxide is determined using a differential conductometric method. The sensitivity limit of the method is 5 Mg/g, the repeatability + 10 % relative. 

Elwell and Wood (39) use the conductometric determinatio of carbon dioxide to determine carbon in titanium and zirconium. The combustion is carried out similarly as in their gravimetric method. The reproducibility is + 10 /ig/g at the 200 g/g level. 

The methods used for measuring the carbon dioxide generated from the organic carbon have also varied considerably. The DOC values found by wet oxidation methods range from 0.5 to 2.0 mg carbon/1., so that the lower values produce about 22 / g carbon dioxide/ml. The greater the sensitivity of the measuring device, the smaller the amount of sample needed. Early methods included gravimetric and volumetric determinations of the released carbon dioxide. More recently, conductometric (23),... 

C02 can also be generated by ionizing radiation in aqueous solutions [114]. For instance, the radical anion can be produced by reaction of hydroxyl radicals or H atoms with formic acid/formate ion, hydroxyl radicals with carbon mmioxide, or solvated electrons with carbon dioxide [115]. In these experiments, the hydroxy carbonyl radical OCOH can also form, (1.13)-(1.16). The latter radical is the protonated form of the CO2 radical anion (1.16). The pKa of OCOH has been a matter of several experimental determinations resulting in significantly different values found for this quantity. A p/sTa (0C0H/C02 ) value of 2.3 has been quite recently determined by von Sonntag et al. [115] by using pulse radiolysis with conductometric detection. 

Mallett (31) recommends combustion in a high-frequency furnace in pure oxygen, followed by conductometric determination of carbon dioxide after absorption in barium hydroxide solution. The combustion can only be carried out when fluxing agents are used. For a 1 g sample, 1 g iron and 1 g tin are generally needed. For materials that are difficult to combust the amount of sample is reduced to 0.5 g. If the sample combusts easily, the amount of iron can be reduced to 0.5 g, the amounts of sample and tin being 1 g. 

Schoch et al. (9) describe the conductometric determination of sulphur dioxide. In the case of high purity copper, samples of about 100 mg are burnt in oxygen at 1400°C in a high-frequency furnace, the sulphur dioxide is absorbed in 0.00125 M sodium hydroxide and determined conductometrically. Carbon dioxide is separated by gaschromatography and can be determined simultaneously. The method which is a micro-method needs a very careful sample preparation and calibration. The reproducibility for sulphur concentrations of 6 /ig/g is said to be 0.3 AMore studies remain however necessary to find out whether the general problem of the non-quantitative transformation of sulphur into sulphur dioxide is solved by this method. 

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