1. Completing the analysis request form (Available from CHN Room in WP 1.11)
Please complete the request form
2. Sample preparation
Ensure that your sample is as pure as it can possibly be, and that it is completely dry. When samples still have trace amounts of solvent present, the weight of your 'sample' will not be accurate - in fact it is often impossible to take a reading from the balance as the weight continually drops as the solvent evaporates (REMEMBER, I NEED TO WEIGH YOUR SAMPLE TO A MILLIONTH OF A GRAM). Even if the solvent is less volatile and doesn't affect the balance reading, it will greatly affect your results. (For an example see Common Problems)
3. How much sample do I need ?
Usually the quantity required for CHN analysis is approximately 1.6mg, however, because some samples tend to have traces of static, or are difficult to collect, we recommend that you submit at least 2mg. Occasionally I will require more than this amount.
When your sample is burned in the combustion tube, water vapour is formed from the hydrogen content of your sample - This water tends to 'wet' the system and gives the internal components a thin coating of water droplets - This is usually not a problem as calibration takes account of this. However, when a sample with low hydrogen content (Typically less than 2%) is run, the system tends to dry up, causing artificially low hydrogen readings. This occurs due to the water vapour produced trying to 're-wet' the system. This has a memory effect (i.e. it affects following samples). Again, this effect can be compsensated for by calibration and by burning a larger weight of sample in order to raise the overall water vapour produced. Bearing this in mind, if your hydrogen content is more than 3%, you should try to submit at least 2mg. If your hydrogen content is less than 3%, you should submit at least 3mg.
Please contact Dr Brian Hutton for further information.