That depends on many factors.

Sample purity, complexity, molecular mass, solubility, access to NMR:

what field what probes, cryoprobe?, how much time do you have available.

Do you need solvent suppression etc.

It would be more helpful to think in terms of concentration and complexity that just an amount.

As far as 13C is concerned, you can try an HSQC. Unless you have a very simple and very very small molecule it is very unlikely that you will get anything running a direct 13C.... assuming this is not 13C labeled.

Thank Dr. Markus Germann.I dont know,, my sample need solvent suppression or not. It is difficult to soluble in common NMR solvents. So, this is problem.

To add to Prof. Germann's answer, what are you trying to get out of the NMR experiment? Is this a protein you are trying to identify, characterize the binding site,determine the exact 3D structure, or assess it's general fold?

No Mr. Dr. Jeffrey Brender. It is a small molecule which promoting the growth of other microorganisms i.e growth promoting compound.

Not a small molecule specialist, but from my experience you should not have difficulty getting 1 and 2D (TOCSY or gradient COSY, NOESY or ROESY) 1H NMR from your sample in a few hours even with a low field instrument (.5 mg =1-2 mM for 500-1000 MW).

Carbon detection (HSQC, HMQC or HMBC) may be more difficult but should be possible. The publication below lists some of the experiments possible, which were all taken at a 1 mm concentration in a 500 MHZ spectrometer. The key factor is the stability of your sample. Using an aprotic solvent like DMSO may help both solubility and stability (lyophilize then resolubilize in DMSO).

http://link.springer.com/protocol/10.1007%2F978-1-61779-618-0_6

Thank Mr. Dr. Jeffrey Brender for your valuable suggestions. I will try--.

Dear NMR colleague,

we have shown that we can do a de-novo structure determination of a low-MW compound (

Thank Mr. Alfred Ross for your information. You used 1H-NMR or 13C-NMR. Really it took one week?

Dear Nazrul,

...we used 1H and 1H-13C correlated (HSQC, HMBC) type of experiments, but hardly ever 13C direct observe. For most cases you can do a structure determination by use of the aforementioned experiments. And yes - it can take one WEEKEND (not one week as you state)...

Regards

Alfred

Dear Dr. Alfred Ross,

Thank you very much. I have 0.1 mg samples but I am confused, is it ok for 1H-NMR? Now you assured me. So, I think, this amount may be ok.

Did you published any article? If yes, please send me your article. I am really gratefull with you.

Dear Dr. Alfred Ross,

Do you please inform me the maker name of your NMR?You use which company's NMR and cryoprobe? This is very important for me.Thank for kindly understand.

Dear Mohammad,

we use a Bruker 1.7 mm Cryoprobe at 500 MHz - how do you know the amount of your sample? What is the expected MW of the compound?

Regrads

Alfred

Thank Dr. Alfred Ross for your information. I already run my sample in HPLC and collected more active fraction, bioassay, evaporated and measure weight. This sample weight is 0.9 mg. This fraction run through LC-MS and I got the following molecular ion peaks (268.15; 312.16 and 339.21). Please see the following attach file. Thank

...hmmm....if the MW is around 339 the 0.9 mg's should be fine to run useable NMR data (1H, 2D 1H-1H [COSY, TOCSY] and 2D 1H-13C HSQC) on basically any NMR machine nowadays available....within a few hours!

Kind regards

Alfred

Thank Dr. Alfred Ross again for your valuable information.

Dear Mohammad,

Did you collect your fractions through prep-HPLC or just from HPLC?

If you use prep-HPLC, do you also need to adjust the elution method, which is different from the one used in HPLC?

If you collect the fractions from HPLC, how long does it take you to get 0.1 mg?

Thanks!

Best regards,

Juan

Thanks Dr. Mohammad for asking such an important question on ResearchGate. It helped me a lot. And thanks to all respondents too. 

I think 0.5 mg is ok. you just need to expand the time of analysis

Dear all. Any of you has analysed mPEG by 1HNMR? I would like an advice on the optimum concentration/mass of the polymer for a 400Hz 1HNMR analysis.

Thanks  

Dear Natalia

I have done mPEG proteins some time back - I'd savely expect a limit of detection (LOD) for mPEG around a few ug's within 5 min's at a 400 MHz RT probehead. If you want to have 13C information I'd begin with 0.1 mg's for HSQC within 1h. 2D homonuclear work (e.g. Diffusion) is somewhere in between. If you are interested in the terminal CH3 of the polymer you need much more...if you are after 13C direct 1D it's even worse.

You see the answer very much depends on what you need...

I hope this helps

Alfred

Thank you very much for your answer Alfred. I am interested to see the amide bond between mPEG-NH2 and a carboxylated small molecule by 1H NMR.

..hmm in this case (PEG-CH2-NH-C=O-X) it very much depends on the MW of the PEG. I would try something like (at least) 100 uM concentration (which is for a 10 kDa PEG about 1 mg/ml or half a mg in a typical NMR tube)...If you have to REALLY prove the bond by HMBC to C=O it can be very tricky (=time consuming) on the NMR machine you have at hand for higher MWs...good luck!

Regards

Alfred