School of EPS: Current Staff & Students

EPS Current Students and Staff

Submitting Samples for Elemental Analysis

1. Completing the analysis request form (Available from CHN Room in WP 1.11)

We require a completed paper copy of the form, brought to WP1.11 along with your sample. Both can be left in the appropriate drop off box in WP 1.11.

Please complete the request form

  • Your sample code should consist of your initials and a number (or code) that refers to an individual sample. This code should be similar to that used for Mass Spec or NMR

  • Obviously, remember to fill in your name!

  • The 'PROJECT' box, should be used to tell me who your supervisor is (current version).

  • If known, give the formula of your sample, or at least give an indication of what it may or should be. It is also useful to draw the structure on the back of the request form. (It is important that I know the types of bonds trying to be broken as stronger bonds occasionally require a combustion aid to be added).

  • It is essential to complete the hazard assessment of your sample, so it can be treated accordingly. Air sensitive samples can be handled, but only if I am told that they are air sensitive on the request form.

  • Unknown toxicity should be noted by writing 'unknown toxicity' in the the hazard section.

  • From your molecular formula, you should be able to deduce your theoretical %CHN content - THIS IS VERY IMPORTANT as your sample will be placed in an order of descending hydrogen content.

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.