Emission-spectrometric determination of nitrogen-15 in trace amounts of N2, NO and N2O after gas-chromatographic separation. A new, combined method for investigating denitrification in soil

The chemical preparation of soil and plant samples and their emission-spectrometric analysis for enrichment in 15N have become routine laboratory procedures; however, the determination of 15N in gaseous mixtures still presents difficulties. Analytical difficulties arise when one is investigating denitrification in soil. In such cases, it is necessary to work with a hermetically sealed chamber. As a result of fertilizer-soil interaction, small amounts of N2, NO and N2O are released into the chamber atmosphere. Helium or neon is used as filler gas. Isotopic analysis of the gases in question is carried out by means of a combination of gas chromatography and emission spectrometry. From the chamber atmosphere, 2ml of gas is drawn off and passed through a separation column filled with PORAPAK Q; the carrier gas is CO2. Preparatory isolation of the separated gaseous components is effected by introducing the gas mixture into a special nitrometer. The nitrogen sample is fed into the discharge tube by means of a dosing faucet. This operation ensures the gas pressure required for high-frequency excitation. The analysis of NO is carried out in a similar way. The error in determining 15N in gas samples is +-3%. (author)