- Reaction score
- 3,025
The primary two methods you will need to have any compound tested for structural confirmation and purity are (1) NMR, and (2) Mass spectroscopy.
You can Google more about these two methods to learn how they work. In short, NMR uses strong magnetic fields to register "spikes" of activity that correspond to either hydrogens (H-NMR) or carbons (C-NMR) in the structure. Based on the shakes and distributions of the spikes, it can allow you to clarify/confirm the general shape of the molecule.
Mass spectrometry also uses strong magnets, but instead just to measure the total mass of each molecule based on how it reacts as a whole to the magnetic field.
So in brief, for structural confirmation:
- NMR can tell you the structure of the compound.
- Mass spec can tell you the molecular mass of the compound.
Both are important, as unless you do a very thorough and expensive NMR assessment (both H-NMR & C-NMR with 2D NMR analysis), it is usually impossible to be 100% certain of the entire structure by NMR. This is because NMR is only looking at your carbons and hydrogens, and sometimes there are nitrogens or other groups in the structure as well.
Mass spec alone is actually quite helpful even, as there will only be so many possible combinations of structures that can register an exact molecular weight.
So with mass spec, a lab will be able to give you a list of maybe 5 possible compound formula. Then with even a basic H-NMR, you should be able to confirm that if the mass was correct, and the H-NMR looks "generally correct", your molecule is likely exactly what you want it to be.
If you want to get the best results for the cheapest cost, request the H-NMR spectrum from your chemical supplier. I have had no problem getting this data from any supplier I have asked. You can submit this H-NMR spectrum to your lab as well for comparison which will make their job easier.
But they can also just check even without a reference to make sure the NMR data "makes sense". NMR data doesn't need to be compared against something, though it does make it easier. NMR data can just be analyzed to see if the spikes of each carbon or hydrogen show up where would generally be expected.
So for a basic confirmation, all you really need is H-NMR (hydrogen NMR) to broadly assess if the structure seems roughly correct and mass spec to confirm the molecular mass is correct. Again, if the molecular mass is correct, there are usually only a finite number of structures it could possibly be. So if the H-NMR also makes sense, you're pretty much guaranteed the compound is correct.
Chemical purity is best done by NMR as well (NMR purity testing), as it does not require a perfect reference sample of the given compound like HPLC would to assess purity.
So, to get something tested, call a chemical testing facility in your area. Private labs can be very expensive. I've heard university chem/NMR labs can be much cheaper. Tell them you have a chemical you wish to have tested for structure and purity, and ask if they will offer and for what price:
1) H-NMR for general structural confirmation
2) Mass spectrometry for molecular mass confirmation
3) NMR purity testing for approximation of purity (optional)
If you request the H-NMR spectrum from your supplier, you can provide it to them for reference when you go to drop off a sample, but again, this should not be truly necessary for a general assessment.
That should cover it.
You can Google more about these two methods to learn how they work. In short, NMR uses strong magnetic fields to register "spikes" of activity that correspond to either hydrogens (H-NMR) or carbons (C-NMR) in the structure. Based on the shakes and distributions of the spikes, it can allow you to clarify/confirm the general shape of the molecule.
Mass spectrometry also uses strong magnets, but instead just to measure the total mass of each molecule based on how it reacts as a whole to the magnetic field.
So in brief, for structural confirmation:
- NMR can tell you the structure of the compound.
- Mass spec can tell you the molecular mass of the compound.
Both are important, as unless you do a very thorough and expensive NMR assessment (both H-NMR & C-NMR with 2D NMR analysis), it is usually impossible to be 100% certain of the entire structure by NMR. This is because NMR is only looking at your carbons and hydrogens, and sometimes there are nitrogens or other groups in the structure as well.
Mass spec alone is actually quite helpful even, as there will only be so many possible combinations of structures that can register an exact molecular weight.
So with mass spec, a lab will be able to give you a list of maybe 5 possible compound formula. Then with even a basic H-NMR, you should be able to confirm that if the mass was correct, and the H-NMR looks "generally correct", your molecule is likely exactly what you want it to be.
If you want to get the best results for the cheapest cost, request the H-NMR spectrum from your chemical supplier. I have had no problem getting this data from any supplier I have asked. You can submit this H-NMR spectrum to your lab as well for comparison which will make their job easier.
But they can also just check even without a reference to make sure the NMR data "makes sense". NMR data doesn't need to be compared against something, though it does make it easier. NMR data can just be analyzed to see if the spikes of each carbon or hydrogen show up where would generally be expected.
So for a basic confirmation, all you really need is H-NMR (hydrogen NMR) to broadly assess if the structure seems roughly correct and mass spec to confirm the molecular mass is correct. Again, if the molecular mass is correct, there are usually only a finite number of structures it could possibly be. So if the H-NMR also makes sense, you're pretty much guaranteed the compound is correct.
Chemical purity is best done by NMR as well (NMR purity testing), as it does not require a perfect reference sample of the given compound like HPLC would to assess purity.
So, to get something tested, call a chemical testing facility in your area. Private labs can be very expensive. I've heard university chem/NMR labs can be much cheaper. Tell them you have a chemical you wish to have tested for structure and purity, and ask if they will offer and for what price:
1) H-NMR for general structural confirmation
2) Mass spectrometry for molecular mass confirmation
3) NMR purity testing for approximation of purity (optional)
If you request the H-NMR spectrum from your supplier, you can provide it to them for reference when you go to drop off a sample, but again, this should not be truly necessary for a general assessment.
That should cover it.