Determination of Organic Matter in Soil Samples

Application note 51 from Exeter Analytical (UK) illustrates how the Carbon, Hydrogen and Nitrogen (CHN) content of soil samples can be precisely and reproducibly determined using their Model 440 Elemental Analyser.

The determination of the Carbon, Hydrogen and Nitrogen (CHN) content of soil samples is of major interest to environmental and agrochemical laboratories throughout the world. Organic matter is known to directly influence the productive capacity of different soils as it is a major contributor of C, H as well as N, P, S and other nutrients. Percentage Carbon can be determined in both its inorganic and organic forms via acid pre-treatment or temperature differential measurement using an Exeter Analytical Model 440 Elemental Analyser. The determination of the Nitrogen content of soils using a Model 440 Elemental Analyser saves considerable time and cost with no diminishment of data quality compared with the traditional Kjeldahl nitrogen determination method.

This application note includes details of the analytical methodology used plus data demonstrating the high quality of CHN data determination that is possible using a Model 440 Elemental Analyser.

The Exeter Analytical Model 440 is a static combustion CHN Elemental Analyser, with a unique horizontal furnace design, which enables easy removal of sample residue between each soil analysis. Consequently one combustion tube will analyse in excess of 1000 soil samples without the need for removal and cleaning. By comparison other elemental analysers, employing vertical furnace designs, will require cleaning after as little as 20 samples. The gas flow characteristics of the Model 440 analyser are superior to other elemental analysers due to the effective elimination of troublesome residue build-up. This thereby provides longer-term calibration stability as well as enhanced accuracy and precision for measured soil sample data.

In addition, as the Model 440 provides complete control over combustion parameters it is able to reproducibly achieve 100% combustion with the widest range of soil samples. Proprietary Nitrogen analysis software uniquely enables accurate measurement of low Nitrogen levels (in the 0.1-0.2% range) with a high degree of accuracy.