Nitrogen Analysis – Determination of Nitrogen Content by Inert Gas Fusion by LSM Analytical

Background

LSM Analytical Services offer a large and diverse range of modern analytical testing facilities that cater for a vast range of industry sectors. LSM’s success has been achieved by building on a strong reputation for low cost, fast accurate turnaround. The laboratory activities are backed up by accreditation to the ISO 17025 (UKAS) and 9001:2000 laboratory and quality management standards. LSM is able to offer complete analytical solutions from its internationally recognised team of technical experts, with in depth knowledge, allowing its customers to benefit from impartial guidance.

LSM’s range of analytical services includes:

•        X-Ray Fluorescence Spectrometry (XRF)

•        X-Ray Diffraction (XRD)

•        ICP Optical Emission Spectrometry (ICP-OES)

•        Atomic Absorption Spectrometry (AAS)

•        Carbon, Sulphur, Nitrogen, Oxygen Analysers

•        Boron analysis by the Neutron Transmission method

•        Colorimetric and Volumetric Analysis

•        Particle Size Analysis

Nitrogen Analysis

LSM Analytical Services large range of analytical techniques includes instrumentation for Nitrogen analysis by the inert gas fusion method.

Inert Gas Fusion Method for Nitrogen Analysis

The inert gas fusion method is used for Nitrogen analysis. This is typically based on a furnace with water-cooled copper electrodes. The principle is to fuse the sample in a high purity graphite crucible in the furnace by taking it to very high temperatures (3000°C) in an inert gas. The carbon crucibles are effectively resistors that supply the heat necessary to fuse the sample. The Nitrogen in the sample is released as molecular Nitrogen (N₂), which is measured using a thermal conductivity cell. For reactive metals a flux is also required to help the release of the Nitrogen from the sample. The most common flux is high purity nickel and the amount added to a sample varies but is typically in the ratio of 10 parts flux to 1 part sample.

The Impact of Impurities

The purity of the gas is an important factor, with gas “scrubbers” or out-gassing being methods to address the potential impact of impurities.

In the test a signal will be obtained that is not attributable to the sample. The cause is a combination of impurities in the gas and crucible. The average contribution to the Nitrogen signal from these sources is determined to allow the sample contribution to be calculated. The inconsistency of impurity levels from these sources cannot be completely eliminated and this affects the ability to determine accurately to very low levels. As the method is relatively quick, repeat determinations are often requested to improve the accuracy of the determination (by taking the average of several results).

Source: LSM Analytical Services

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