Duma's Method

It is thus an important analytical chemistry technique, basically applied in the determination of nitrogen content in different substances. The Dumas Method was devised during the 19th century by Jean-Baptiste Dumas and currently represents the procedure that has reached a very high development stage, allowing fast and precise nitrogen analysis, mostly regarding food products. The Dumas Method was important not only for the laboratory but also for agriculture, food science, and environmental monitoring.

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This Story also Contains

1. Dumas Method
2. Aspects of the Dumas Method
3. Relevance and Applications of the Dumas Method
4. Some Solved Examples
5. Summary

It is through the knowledge of nitrogen content in organic materials that information on the levels of protein is explained to be available in the material. This is very important to nutritional labeling by researchers and quality assessment by manufacturers. On the practical side, it affords food manufacturers a pathway to find out whether their products meet regulatory standards regarding their declared protein content. This is very critical at a time when consumers are very keen about health and would want to know everything about the nutritional information.

Dumas Method

The Dumas technique is an analytical method for the quantitative determination of nitrogen in chemical substances. Working principle: The principle of this technique is combustion, whereby the sample undergoes high temperatures in excess oxygen, generally within a temperature range of 800°C to 1000°C. Such conditions would convert nitrogenous compounds into nitrogen gas, carbon dioxide, and water. Further analysis of the gases obtained from the analysis gives an estimate of nitrogen content.

These advantages greatly include, over the traditional techniques, including the Kjeldahl method, speed, and the absence of toxic chemicals. With the automation of the Dumas method, much time can now be saved in analysis because it makes the technique very suitable for high-throughput environments. It is now commonly used in food science in determining the protein content of samples because nitrogen content is convertible to the level of protein through specific conversion factors.

The nitrogen-containing organic compound, when heated with copper oxide in an atmosphere of carbon dioxide, yields free nitrogen in addition to carbon dioxide and water.

$\mathrm{C}_{\mathrm{x}} \mathrm{H}_{\mathrm{y}} \mathrm{N}_{\mathrm{z}}+(2 \mathrm{x}+\mathrm{y} / 2) \mathrm{CuO} \longrightarrow \mathrm{xCO}_2+\mathrm{y} / 2 \mathrm{H}_2 \mathrm{O}+\mathrm{z} / 2 \mathrm{~N}_2+(2 \mathrm{x}+\mathrm{y} / 2) \mathrm{Cu}$
Traces of nitrogen oxides formed, if any, are reduced to nitrogen by passing the gaseous mixture over a heated copper gauze. The mixture of gases so produced is collected over an aqueous solution of potassium hydroxide which absorbs carbon dioxide. Nitrogen is collected in the upper part of the graduated tube as shown in the figure.
Let the mass of organic compound = mg
The volume of nitrogen collected = V₁ mL
Room temperature = T₁K

Volume of nitrogen at $\mathrm{STP}=\frac{p_1 V_1 \times 273}{760 \times T_1}$
Where p₁ and V₁ are the pressure and volume of nitrogen, p₁ is different from the atmospheric pressure at which nitrogen gas is collected. The value of p₁ is obtained by the relation;
p₁ = Atmospheric pressure – Aqueous tension
22400 mL N₂ at STP weighs 28g.

$\begin{aligned} & V \mathrm{~mL} \mathrm{~N}_2 \text { at STP weighs }=\frac{28 \times V}{22400} \mathrm{~g} \\ & \text { Percentage of nitrogen }=\frac{28 \times V \times 100}{22400 \times m}\end{aligned}$

Aspects of the Dumas Method

The Dumas technique consists of a few steps that enable it to work effectively as a nitrogen analysis technique. These include the following:

1. Combustion: This is high-temperature combustion in an atmosphere enriched with oxygen. This is a very fundamental stage since the organic materials get broken down, consequently liberating nitrogen in the form of nitrogen oxides (NOx).

2. Reduction: Pass combustion gases, now containing nitrogen oxides, into a reduction furnace. A reducing agent inside, typically copper, reduces the nitrogen oxides to nitrogen gas.

3. Scrubbing: Passing the gases through scrubbing agents removes other by-products of combustion, mainly water and carbon dioxide. These scrubs isolate the nitrogen gas for measuring.

4. Detection: The nitrogen gas is read using a thermal conductivity detector or another type of gas analyzer, which enables an accurate reading to be obtained for nitrogen content.

These factors make the Dumas Method such a versatile and efficient tool and thus very much favored in many analytical laboratories.

Relevance and Applications of the Dumas Method

The Dumas technique has important applications in several fields, primarily the food sciences and environmental analysis. Food industries are interested in nitrogen determination, as it is an element in the critical constituents in nutritional labeling, where the amount of nitrogen is proportionately Square to the content of protein. One example of the application of the Dumas method is in how the food industry applies the method to ensure compliance with the labeling regulations among food manufacturers so that appropriate nutrition information is availed for consumers.

In agricultural research, the Dumas Method is applied in the determination of nitrogen levels in soils and plants toward work on sustainable farming. The determination of nitrogen availability helps optimize fertilizer application to farmers for good crop yields while minimizing effects on the environment.

The Dumas method is further applied in environmental monitoring, in particular, for the determination of nitrogen levels in water and soil samples, a critical aspect of the assessment of pollution levels and the impact on ecosystems of the nitrogen cycle.

Case studies on the Dumas Method are included, which prove it through examples—such as examining the nitrogen content in several grains—and discuss the swiftness and accuracy of the method against more traditional techniques. Results not only shed light on the nutritional value of grains but also inform farming practices.

While the Dumas technique is one of the cardinal tools in nitrogen analysis, which has undergone revolutionizing changes in its use by various industries, the very efficiency, exactitude, and versatility achieved render it an invaluable tool for researchers and manufacturers.

Recommended topic video on (Duma's Method )

Some Solved Examples

Example 1
Question:

According to Duma's method percentage of N in an organic compound can be calculated by:

$\begin{aligned} & \text { 1) } \\ & \frac{1.4 \times \mathrm{N} \times \mathrm{V}}{\text { mass of } \mathrm{O} . \mathrm{C}} \\ & \text { 2) (correct) } \\ & \frac{28 \times \text { vol. of } \mathrm{N}_2(\mathrm{in} \mathrm{ml}) \text { at STP }}{224 \times \text { mass of } \mathrm{O} . \mathrm{C}} \\ & \text { 3) } \\ & \frac{12 \times \text { mass of } \mathrm{CO}_2 \times 100}{44 \times \text { mass of } \mathrm{O} . \mathrm{C}} \\ & \text { 4) } \\ & \frac{12 \times \text { mass of } \mathrm{CO}_2 \times 100}{44 \times \text { mass of } \mathrm{O} . \mathrm{C}}\end{aligned}$

Solution:

As we have learned,

Dumas method- Quantitative analysis of nitrogen

$\begin{aligned} & \text { Volume of Nitrogen at STP }=\frac{\mathrm{P}_1 \mathrm{~V}_1 * 273}{760 * \mathrm{~T}_1} \\ & \begin{aligned} \% \text { of Nitrogen } & =\frac{28 \times \mathrm{vol} . \text { of } \mathrm{N}_2(\mathrm{in} \mathrm{ml}) \text { at } \mathrm{STP} \times 100}{22400 \times \text { mass of } \mathrm{OC}} \\ & =\frac{28 \times \mathrm{vol} \text { of } \mathrm{N}_2(\mathrm{in} \mathrm{ml}) \text { at STP }}{224 \times \text { mass of } \mathrm{OC}}\end{aligned}\end{aligned}$
Hence, the answer is the option (2).

Example 2
An organic compound is estimated through the Dumas method and was found to evolve 6 moles of CO₂, 4 moles of H₂O, and 1 mole of nitrogen gas. The formula of the compound is:

1) $\mathrm{C}_{12} \mathrm{H}_8 \mathrm{~N}$
2) $\mathrm{C}_{12} \mathrm{H}_8 \mathrm{~N}_2$
3) $\mathrm{C}_6 \mathrm{H}_8 \mathrm{~N}_2$
4) $\mathrm{C}_6 \mathrm{H}_8 \mathrm{~N}$

Solution:

In the Duma's Method,

Carbon atoms are converted to CO₂, Hydrogen atoms are converted to H₂O, and Nitrogen atoms are converted to N₂

$\mathrm{C}_{\mathrm{x}} \mathrm{H}_{\mathrm{y}} \mathrm{N}_{\mathrm{z}} \longrightarrow 6 \mathrm{CO}_2+4 \mathrm{H}_2 \mathrm{O}+\mathrm{N}_2$

$
\begin{aligned}
& 6 \mathrm{C} \rightarrow 6 \mathrm{CO}_2 \\
& 8 \mathrm{H} \rightarrow 4 \mathrm{H}_2 \mathrm{O} \\
& 2 \mathrm{~N} \rightarrow \mathrm{N}_2
\end{aligned}
$

Thus, the formula of the compound is $\mathrm{C}_6 \mathrm{H}_8 \mathrm{~N}_2$.

Hence, the answer is the option (3).

Example 3

In Dumas method for the estimation of N₂, the sample is heated with copper oxide and the gas evolved is passed over :
1)Copper oxide

2) Ni

3)Pd

4) Copper gauze

Duma’s method. The nitrogen-containing organic compound, when heated with CuO in an atmosphere
of CO₂, yields free N₂ in addition to CO₂ and H₂O.

$\begin{aligned} \mathrm{C}_{\mathrm{x}} \mathrm{H}_{\mathrm{y}} \mathrm{N}_{\mathrm{z}}+\left(2 \mathrm{x}+\frac{\mathrm{y}}{2}\right) \mathrm{CuO} & \rightarrow \mid \\ & \mathrm{xCO}_2+\frac{\mathrm{y}}{2} \mathrm{H}_2 \mathrm{O}+\frac{\mathrm{z}}{2} \mathrm{~N}_2+\left(2 \mathrm{x}+\frac{\mathrm{y}}{2}\right) \mathrm{Cu}\end{aligned}$

Traces of nitrogen oxides formed, if any, are reduced to nitrogen by passing the gaseous mixture over heated copper gauze.

Hence, the answer is the option (2).

Summary

The Dumas technique is one of the key powerful techniques used in the analysis of nitrogen. High-temperature oxidation, followed by gas analysis, is an efficient technique that enables the rapid estimation of nitrogen content with quite a high accuracy. In view of the definite advantages it has over conventional techniques like the Kjeldahl method, the Dumas technique seems to be pretty well adopted in food science, agriculture, and environmental monitoring.