Thursday 19 January 2012

Dumas Method For Nitrogen Estimation

Dumas Method

The Dumas method in analytical chemistry is a method for the quantitative determination of nitrogen in chemical substances based on a method first described by Jean-Baptiste Dumas over a century and a half ago.[1]
An automated instrumental technique has been developed which is capable of rapidly measuring the crude protein concentration of food samples and is beginning to compete with the Kjeldahl method as the standard method of analysis for protein content for some foodstuffs.
General Principles

A sample of known mass is combusted in a high temperature (about 900 oC) chamber in the presence of oxygen. This leads to the release of CO2, H2O and N2. The CO2 and H2O are removed by passing the gasses over special columns that absorb them. The nitrogen content is then measured by passing the remaining gasses through a column that has a thermal conductivity detector at the end. The column helps separate the nitrogen from any residual CO2 and H2O that may have remained in the gas stream. The instrument is calibrated by analyzing a material that is pure and has a known nitrogen concentrationsuch as EDTA (= 9.59%N). Thus the signal from the thermal conductivity detector can be converted into a nitrogen content. As with the Kjeldahl method it is necessary to convert the concentration of nitrogen in a sample to the protein content, using suitable conversion factors which depend on the precise amino acid sequence of the protein.
Advantages and Disadvantages


Advantages: It is much faster than the Kjeldahl method (under 4 minutes per measurement, compared to 1-2 hours for Kjeldahl). It doesn't need toxic chemicals or catalysts. Many samples can be measured automatically. It is easy to use.
Disadvantages: High initial cost. It does not give a measure of the true protein, since all nitrogen in foods is not in the form of protein. Different proteins need different correction factors because they have different amino acid sequences. The small sample size makes it difficult to obtain a representative sample.


2 comments:

  1. i want formula's for dumas method please!

    ReplyDelete
  2. go to this link for calculation.
    http://www.tutorvista.com/content/chemistry/chemistry-iii/organic-compounds/quantitative-analysis.php

    ReplyDelete