Previous

Next

The clean sample gases now pass through a gas chromatograph column to separate the N2 from the other gasses . The sample gas pulses and a separate reference stream of helium pass through a detector; differences in thermal conductivity between the two streams are displayed as visible peaks and recorded as numerically integrated areas.

Linear regression applied to combustion of known standard materials yields a regression line by means of which peak areas from unknowns are converted into total element values for each sample. In this way the amount of Nitrogen is measured.

Dumas method (or combustion method)

The Dumas method serves as a more precise and efficient alternative to Kjeldahl. With the Kjeldahl method, digestion, distillation and titration can take up to 1.5 to 2 hours. With the Dumas method, protein analysis time can be reduced to minutes. Precision is also increased.

For food composition databases almost always the Kjeldahl method is used. However, the Dumas method becomes more and more an accepted alternative for the Kjeldahl method.

Advantages:

• Low analysis time.

• Many samples can easily be measured automatically.

Disadvantages:

• Only small and dry samples (5-50 mg) can be analyzed.

• High initial costs.