School of EPS: Current Staff & Students

EPS Current Students and Staff

CHN Solvent Calculator Instructions

Heriot-Watt University
EPS - Chemistry


Calculator for CHN analysis with Solvent Correction

Copyright ©2000 Gareth Evans

 

Instructions for %CHN calculator with solvent correction

Before you use this calculator your sample needs to meet the following criteria:-

  1. You have submitted this sample for CHN anlysis and have results that are outwith experimental error.
  2. The sole impurity in your sample is a single solvent or other substance.
  3. You can identify this solvent / substance (from NMR/Mass Spec/IR etc).

If you can answer yes to all of the above, the calculator may be able to identify the quantity of solvent in your sample that would give %CHN results matching your returned values. Proceed as follows -

  1. Select the solvent you suspect present in your sample (this is done using the drag down menu). If your solvent is not listed, and you feel it is a common solvent (NOT Pet Ethers etc, as they are mixtures of various solvents), please contact  Dr Brian Hutton to add this to the list of predefined solvents. Alternatively, you can select 'Other' from the drop down list and use the boxes to the right to define the solvent / impurity that you are working with.

    *
    Note that if you are selecting a predefined solvent from the dropdown list, you MUST NOT alter the boxes defining the Solvent / Impurity.
    If you are using 'Other' as your solvent, enter the number of carbons, hydrogens, and nitrogens in one mole of your solvent / impurity and also the total molar mass.
    You should also name your solvent/impurity and this will appear on your results report.

  2. Enter the maximum number of moles of solvent suspected in your sample. If you have no idea, start with a small value (less than 1) and increase if necessary. It is worth noting that about 0.05 moles of solvent per mole of compound can affect your CHN results considerably.
  3. Enter the formula of your sample. If you are not sure how to use this type of calculator, read the instructions for the CHN calculator.
  4. Enter your CHN results, quoting to two decimal places.
  5. Enter the error margin - In order to quote CHN results you are allowed an error of +/-0.3%, so this is usually the value you would enter. However, if the calculator returns hundreds of matches, you could reduce this error margin to 'home-in' on the most likely solvent contents. Conversely, if you do not obtain any results from the calculator, you could try increasing the error margin to force the calculator to consider more solvent contents.
  6. Enter the 'Step' value - This is the amount the calculator increments the solvent content by between each calculation. Obviously, the smaller the increment, the longer the calculation will take. You should start with a value of about 0.005 moles. If you receive too many results, you could increase the step value, or decrease it to improve the liklihood of finding a result match.
  7. Select the type of report that you would prefer -

    • Display only good results - This is the most common type of calculation. This will only report results that meet all of the above criteria.
    • Display all results - You should use this calculation if you are unsure of the amount of solvent / impurity in your sample. This method takes considerably longer, but it can be used to give you an indication of solvent content, and by following the trends reported, you should be able to narrow your search.
When the calculation begins, the computer will report to you the number of full calculations it will perform, and how many solvent 'amounts' it will calculate for.
Depending on the complexity of the calculations and your processor speed and memory resources, your browser may report that there is a script causing the page to slow down and it will ask if you want to stop the script or not. Click on the NO button to continue with the calculations (if you click YES, the program will end and wait for you to click on the Back button to try again). This warning message may appear several times during a complex calculation, but just keep clicking on NO until it has finished.

Return to %CHN Solvent Calculator

Link to Heriot-Watt Elemental Analysis Home Page


Please contact  Dr Brian Hutton   for further information.