Samples are precisely weighed precisely into tin capsules and dropped at pre-set times into a combustion tube (at 1000°C). A constant stream of helium is maintained through tube.
- Helium stream replaced by pure oxygen for 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, sulfur and other interferences.
- Water and carbon dioxide removed by passing gases through scrubbing tubes.
- Remaining nitrogen gas is quantitatively measured by a thermal conductivity detector.
- Protein value is normally calculated using a factor of 6.25 unless otherwise specified.
The technique is generally free of interferences.