• Samples are precisely weighed into silver boats or capsules that have been acidified by 1:1 hydrochloric acid and digested at 80°C.
  • This eliminates carbonates as carbon dioxide. 
  • After final encapsulation samples are dropped at pre-set times into a combustion tube (at 1000°C). A constant stream of helium is maintained through the tube.
  • Helium stream replaced by pure oxygen for a brief period prior to sample introduction.
  • Sample is instantaneously burned.
  • Resulting combustion gases passed over catalysts to ensure complete oxidation and absorption of halogens, sulphur and other interferences.
  • Excess oxygen is removed as gases are swept through reduction tube containing copper at 650°C.
  • Carbon dioxide separated from other unwanted gases on a chromatographic column and quantitatively measured by a thermal conductivity detector.


The technique is generally free of interferences.

  • A few silicon and organo-metallic compounds exhibit a tendency to form stable carbides.
  • Samples containing phosphorus may not combust successfully and give low carbon values.
  • All of these problems can be remedied with the addition of additives to the sample, including most inorganic compounds such as carbides and nitrides.

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