LSM Analytical Services large range of analytical techniques includes instrumentation for Sulphur analysis.
How Sulphur Content is Determined
The principle of Sulphur analysis is to oxidise the sample by heating in an Oxygen atmosphere to form SO2, which is then measured by infrared detector.
Heating of Samples to Determine Sulphur Content
The heating is generally done in a high frequency induction furnace as this provides both speed and accuracy. The sample is placed in a ceramic crucible and an accelerator is often added to ignite the sample and can also act as a flux to dissolve any oxide skins to improve melt fluidity, which allows the Sulphur in the sample to be oxidised in a short time. It is imperative that complete combustion is achieved in order to gain accurate results. There is a large range of accelerators used and the choice depends on the base material being analysed. One feature of any accelerator is a low Sulphur (and Carbon as this is often analysed for in a similar way) content.
The Accuracy of Sulphur Determination Measurements
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, crucible and accelerator. The average contribution to the Sulphur 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).
The Affect of Water on Sulphur Content Measurements
Sulphur results can be affected if water is present in the sample. However dealing with this issue is not straightforward. Residual water can be dealt with by heating the sample to 110°C for one hour. Crystalline water is less easy to deal with as the high temperatures required to dissociate it also mean combustion of the Sulphur.