[Woodwardt84]

Hi again
I have a problem on a compound that  have tried to get elementary pure. Water seems to be stuck on it even after vacuum 7 days 40 degrees C. Is there any way on fixing the small error on the elementar analysis by adding water? I heard something about some people fixing it by using excel and some calculation to take the water amount in the sample into acount.

Kim

[Doc Oc]

1) What can you tell me about the compound?  Some things just won't get completely dry, and as long as the water peak in the NMR is small, it's acceptable even for publication.

2) Are you sure it's not your solvent that's wet?  What solvent are you using?

3) I've heard of people adding D₂O to take exchangeable protons out of the spectrum, but I don't know if this works for plain water.

4) You don't need an Excel sheet to integrate the water out.  If you have a characteristic peak of your compound and you know the exact number of protons it is, you can divide the water peak by that number to determine the amount of water there is relative to your compound.

[fledarmus]

I think I know what you are talking about, Woodward84. If the CHN analysis for your compound comes out wrong, you can try calculating the compound as a hydrate or dihydrate. For example, if your compound is C_xH_yO_z and doesn't give the same percent compositions, try C_xH_yO_z ^.H₂O. If you just assume that the impurity in your analysis is water, you can also back-calculate the number of moles of water required to make your formula match your analysis. That back-calculation is what shows up in a lot of simple excel spreadsheets to calculate the amount of water in your molecule. It's fairly simple math - go ahead and try to set it up.

Whether this type of CHN should be published or presented is an ongoing argument.