The quality of the sample can have a significant impact on the quality of its NMR spectrum. The following is a brief list of suggestions to ensure high sample quality.
- Use clean and dry NMR tubes to avoid contaminating the sample.
- Use good to high quality NMR tubes (Wilmad company, 507 or higher) to avoid unnecessary difficulties in shimming.Supplies
- Filter the sample solution, if necessary, through a tight cotton tip placed in the pipette before pouring it into the NMR tube. Invisible particles suspended in solution will impede obtaining a good line shape.
- Always use the same sample volume. This minimizes the shimming that needs to be done between sample changes. Recommended value for 5 mm tubes: 0.7 mL. The height of the solution in the NMR tube should be ca 5 cm.
- Use the depth gauge to position the sample tube correctly in the spinner. Correct positioning of the sample has high importance for shimming.
- Wipe the sample tube clean before inserting it into the spinner. The top part of the NMR sample tube must be closed with a tight plastic cap for safety purposes.
- Check that the sample tube is held tightly in the spinner so that it does not slip during an experiment.
- The minimum amount of compound depends on the nucleus of interest and also on the spectrometer, particularly on the probe. To get a good quality 1H NMR spectrum use 5-10 mg sample. The concentrated samples will yield broader lines in the spectrum due to increased viscosity. For a 13C NMR spectrum more than 30 mg is preferable.
