What is the minimum amount of sample required for different kinds of NMR analysis (1H, 13C, 2D NMR etc.)? Does the amount will be vary for different NMR instruments depending on the strength (like 500 mhz, 600 mhz etc)?
An excellent question, really, but I am at a loss to answer it, though I should be qualified enough. One thing is a routine, fast acquisition with a standard 5 mm tube of a solution of relatively small molecule which is the dominant substance in the sample. Then it might be maybe a microgram for 1H and a milligram for 13C on a standard high field instrument. But it all depends on a long list of conditions and desiderata:
1) You should ask about molar concentration (molality), refered to the specific nuclei that you need to observe; total amount of sample is meaningless. For example, if you are looking for impurities in, say, aspirin, it is a completely different question than looking at the aspirin molecule itself.
2) Can you afford higher concentration in a smaller volume? 3 mm tubes, or even microfluidic probe with nanoliter volumes (they have better molar sensitivity).
3) Field strength, as you mention. It goes (very roughly) inversely with the square of field strength, and it may depend on instrument make and its current state of maintenance. In general, its a big deal when you switch from 200 MHz to 800, not really too much when the jump is from 500 to 600
4) How much time can you give it? Sensitivity goes inversely with the square root of the accumulation time, roughly. So, considering 1 minute overhead, the difference between 1 minute and 1 hour measurements is really huge.
5) Do you have access to a cryo-probe?
6) What do you mean by "different kinds of NMR analysis"; does it include 2D's, 3D's, MAS, DOSY, HR relaxation time measurements, reaction kinetics, ...
An exhaustive and competent answer would take a review of a considerable size, I think. If you narrow down the question, I am sure that you will start getting a lot of answers.
Stan Sykora Actually I am isolating compounds from plant extracts. After completing isolation I have to go for structure elucidaton of the isolated compounds. For that purpose, I have to sent my samples to the NMR facilty, and they are asking like 5 mg for 1H NMR, 20 mg for 13C NMR. So I have asked the question. Because I have seen in paper, people isolate 2.5 mg or less amount and perormed NMR analysis (1H, 13C, 2D etc).
I see. Yes, that makes sense, and the numbers are reasonable, both on your side and on their side. They of course prefer a good amount of sample so that the analysis will not take too long time and the spectra will be of good quality, making their life easier. You are off by a factor of 2, and I now understand that for you that might indeed mean a lot of effort in sample preparation. But a factor of 2 is something you might be able to negotiate. Between 1 mg and 5 mg it should be basically a matter of instrument time that it takes (especially 13C), and therefore of analysis cost, not of feasibility.
As always, Stan has covered a lot of the key considerations. You don't say what field you have available in the NMR facility or whether they have a cryoprobe. Looking at their specifications I suspect that they don't have a cryoprobe and are operating around 500MHz. If your material is clean and has a molecular weight of
in CDRI can anyone tell what minimum quantity should I send for NMR and IR and MS?
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