Carbon/hydrogen analysis, combustion-tube

The method described above has been used successfully for the determination of compounds such as 3-aminoacetophenol, 8-hydroxyquinoline, 7-hydroxy-7-chloroaniline and benzoic acid, etc. The absolute error was 0.5% for carbon and 0.1% for hydrogen. The reproducibility was checked on the basis of benzoic acid analyses. For carbon, deviations from the mean value were 0.58%. The total duration of the analysis, including combustion of the sample, separation and chromatography, is 20 min per sample. Working continuously, one can introduce a fresh sample into the combustion tube every 10 min. 

Cylinders of the flashed gas were analysed for hydrocarbon gas composition on a Carle gas chromatograph (GC) system equipped with both a thermal conductivity detector (TCD) and a flame ionization detector (FID). An offline preparation system and dual inlet mass spectrometer (MS) were used to analyse the carbon and hydrogen isotopic values of hydrocarbon components. A customized Gow Mac GC was interfaced with a vacuum/combustion system to separate hydrocarbons from other components and combust to CO2 and water that were purified and sealed into Pyrex tubes for isotopic analysis. The CO2 was analysed directly on one of three dual inlet mass spectrometers Finnigan Delta S, Finnigan Delta + XL or VG SIRA II. The water was reacted with zinc turnings and converted to hydrogen gas, which was analysed on either the Delta S or Delta + XL MS. 

Elemental analyses (C, H, N and ash) were carried out by combustion at 900°C, using a procedure and apparatus similar to that described in Stump and Frazer (1973). Carbon dioxide, nitrogen and hydrogen were purified, measured volumetrically, and sealed in Pyrex tubes for isotopic analysis. The sulfur content was determined by Galbraith Laboratories, Knoxville, Tennessee. The high sulfur values may in part reflect inorganic sulfide decomposition during pyrolysis (Table 2). 

An analyzer for the analysis of hydrogen and oxygen isotope values only has one pyrolysis furnace, as opposed to the combustion and reduction tubes in the EA for the measurement of carbon and nitrogen isotope values. The reaction tube packing can be varied depending on the application. 

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