CHN TOTAL CARBON, HYDROGEN & NITROGEN

  • Samples weighed precisely into tin capsules and dropped at pre-set times into 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 instantaneously burned (flash combustion) followed by intense oxidation of tin capsule at 1800°C.
  • Resulting combustion gases passed over catalysts to ensure complete oxidation and absorption of halogens, sulphur and other interferences.
  • Excess oxygen removed as gases are swept through reduction tube containing copper at 650°C. Any oxides of nitrogen reduced to nitrogen gas.
  • Gases are then separated on chromatographic column into N, C, and H. These gases are quantitatively measured by a thermal conductivity detector.

Interferences

This 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.
  • The analysis of numerous fluorine containing compounds will cause errors in the hydrogen result.

All the above problems can be remedied with the addition of additives to the sample.


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