Application Note Nitrogen by Dumas

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Dumatherm with Autosampler

Dumatherm with Dumatherm Manager

Despite appearing to be a relatively new method Nitrogen determination by combustion is actually older the more common than the Kjeldahl method. Jean-Baptiste André Dumas published the Nitrogen method in 1841. This traditional method determines the Nitrogen content by oxidising the sample at high temperature and then analysing the resulting gasses.

The method offers greater speed of analysis and uses no acids or alkalis. A wide variety of samples can be analysed including food, feed, soil, grain, polymers, fuel etc.

The method is performed as follows:

Samples between 50 and 40mg are weighed into tin foils and placed on the auto-sampler carousel. Samples are dropped into the pure camber were all oxygen is removed. The sample is then dropped into the furnace at around 1000°C. Oxygen is injected into the furnace to burn the sample and oxidise the Nitrogen.

Within the reaction chamber the ash is removed and catalytic beds ensure complete combustion of the sample. Controlling the gas flow carefully reduces sooting within the unit and reduces maintenance and downtime. 

In the next stage the Nitrogen is reduced back to elemental Nitrogen by using a copper reduction catalyst. Oxygen, water, and Carbon dioxide are all removed before the Nitrogen passes over the detector.

Passing the gas over a Thermal Conductivity Detector completes the volumetric determination of the nitrogen content. From the amount of Nitrogen detected in the sample and knowing the weight of the sample introduced into the system the % protein can be determined.

Gerhardt supply the Dumatherm system, with either manual sample entry or a 40 place auto-sampler which can be extended to 120 places. Both manual and auto-sampler models are operated by Dumatherm Manager software for complete control and data handling.

For a Printable questionnaire prior to a Dumatherm quotation - click here.

For more information on the Kjeldahl Nitrogen method – click here.

For more information on the Gerhardt Dumatherm system – click here.