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).