School of EPS: Current Staff & Students

EPS Current Students and Staff

Some Common Problems

  • Please do not include any symbols (eg. -, +, *, /, #, (, ), etc.) in your user code as they are sometimes used by the system software to control the analyser.

  • Remember to submit the correct amount of sample - 2mg min. for samples with expected %H content above 2% and 3mg min. for samples with expected %H content below 2%.

  • Occasionally, samples are sumbitted with very low %H values (~0.3%) - Bear in mind that your analysis will have an error of ±0.3%. This may make your results meaningless!

  • Before submitting samples, ensure that they have been purified as much as possible, and there is no residual solvent present (thoroughly dry samples under vacuum if possible, or in drying ovens).

  • Trace amounts of solvent, will cause the apparent 'weight' of your sample to be wrong, and hence give wrong %CHN values, and usually 'wet' samples cannot be weighed at all, as the weight decreases rapidly (millionths of a gram), as solvent evaporates

     Example - A sample of phenyl hydrazine (1.6mg) containing 2% w/w methanol.

     C6H5NHNH2 - 108.14g/mol

     1.6mg 'sample' is actually -
   1.568mg Phenyl hydrazine (1.450 x10-2 mmol)
   0.032mg MeOH (9.988 x10-4 mmol)

     Theoretical formula - C6H8N2
     Actual formula - C6H8N2 . 0.069MeOH

     In other words - C6.069H8.276N200.069

%C %H %N
Theoretical 66.62 7.47 25.91
Actual 66.04 7.57 25.39

Your results would not be good enough for publication
You would now have to purify your sample, dry it properly, and then resubmit !
This costs time and money
So get it right first time !!!!!

Please contact Dr Brian Hutton for further information.