Dumas method
Encyclopedia
The Dumas method in analytical chemistry
is a method for the quantitative determination of nitrogen
in chemical substance
s based on a method first described by Jean-Baptiste Dumas
over a century and a half ago.
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.
The method consists of combusting a sample of known mass in a high temperature (about 900°C) chamber in the presence of oxygen
. This leads to the release of carbon dioxide
, water
and nitrogen
. The gases are then passed over special columns that absorb the carbon dioxide and water. A column containing a thermal conductivity detector at the end is then used to separate the nitrogen from any residual carbon dioxide and water and the remaining nitrogen content is measured. The instrument must first be calibrated by analyzing a material that is pure and has a known nitrogen concentration. The measured signal from the thermal conductivity detector for the unknown sample can then be converted into a nitrogen content. As with the Kjeldahl method
, conversion of the concentration of nitrogen in a sample to the crude protein content is performed using conversion factors which depend on the particular amino acid sequence of the measured protein.
The Dumas method has the advantages of being easy to use and automated. It is also considerably faster than the Kjeldahl method
, taking a few minutes per measurement, as compared to the hour or more for Kjeldahl. It also does not make use of toxic chemicals or catalysts. One major disadvantage is its high initial cost. Also, as with Kjeldahl, it does not give a measure of true protein, as it registers nonprotein nitrogen, and different correction factors are needed for different proteins because they have different amino acid sequences. Finally, the small sample size raises the risk of obtaining an unrepresentative sample.
Analytical chemistry
Analytical chemistry is the study of the separation, identification, and quantification of the chemical components of natural and artificial materials. Qualitative analysis gives an indication of the identity of the chemical species in the sample and quantitative analysis determines the amount of...
is a method for the quantitative determination of nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
in chemical substance
Chemical substance
In chemistry, a chemical substance is a form of matter that has constant chemical composition and characteristic properties. It cannot be separated into components by physical separation methods, i.e. without breaking chemical bonds. They can be solids, liquids or gases.Chemical substances are...
s based on a method first described by Jean-Baptiste Dumas
Jean-Baptiste Dumas
Jean Baptiste André Dumas was a French chemist, best known for his works on organic analysis and synthesis, as well as the determination of atomic weights and molecular weights by measuring vapor densities...
over a century and a half ago.
An automated instrumental technique has been developed which is capable of rapidly measuring the crude protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
concentration of food samples and is beginning to compete with the Kjeldahl method
Kjeldahl method
The Kjeldahl method or Kjeldahl digestion in analytical chemistry is a method for the quantitative determination of nitrogen in chemical substances developed by Johan Kjeldahl in 1883.- Method :...
as the standard method of analysis for protein content for some foodstuffs.
The method consists of combusting a sample of known mass in a high temperature (about 900°C) chamber in the presence of oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
. This leads to the release of carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
, water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
and nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
. The gases are then passed over special columns that absorb the carbon dioxide and water. A column containing a thermal conductivity detector at the end is then used to separate the nitrogen from any residual carbon dioxide and water and the remaining nitrogen content is measured. The instrument must first be calibrated by analyzing a material that is pure and has a known nitrogen concentration. The measured signal from the thermal conductivity detector for the unknown sample can then be converted into a nitrogen content. As with the Kjeldahl method
Kjeldahl method
The Kjeldahl method or Kjeldahl digestion in analytical chemistry is a method for the quantitative determination of nitrogen in chemical substances developed by Johan Kjeldahl in 1883.- Method :...
, conversion of the concentration of nitrogen in a sample to the crude protein content is performed using conversion factors which depend on the particular amino acid sequence of the measured protein.
The Dumas method has the advantages of being easy to use and automated. It is also considerably faster than the Kjeldahl method
Kjeldahl method
The Kjeldahl method or Kjeldahl digestion in analytical chemistry is a method for the quantitative determination of nitrogen in chemical substances developed by Johan Kjeldahl in 1883.- Method :...
, taking a few minutes per measurement, as compared to the hour or more for Kjeldahl. It also does not make use of toxic chemicals or catalysts. One major disadvantage is its high initial cost. Also, as with Kjeldahl, it does not give a measure of true protein, as it registers nonprotein nitrogen, and different correction factors are needed for different proteins because they have different amino acid sequences. Finally, the small sample size raises the risk of obtaining an unrepresentative sample.