Sample Preparation

The use of substandard and/or dirty NMR tubes can damage the NMR probes. Only good quality NMR tubes are approved for use in this NMR Facility. NMR tubes must be kept externally clean!

-In addition, any NMR tube that does not fit properly into the spinner turbine (loose or tight) is not allowed.

-Wipe the NMR tubes and spinner with a Kimwipe before inserting them into the instrument. Tubes and spinners should be as clean as possible to prevent contamination and build up of dirt and grime inside the probe and on the spinner shelf. This build-up causes spinning and shimming problems.

-Always use the depth gauge to position the sample correctly in the spinner prior to lowering it into the magnet.

-Make sure that your NMR sample tube is held tightly in the spinner so that it does not move during the experiment.

To get Good NMR results

Labelling of samples.

Please ensure all samples brought into the NMR labs are labelled using the tickets provided with the following details:

• Your Name
• Sample Number or identification
• Date.
• Solvent.
• All samples will be treated as hazardous.
  Please do not stick labels directly on the NMR tubes.

Making up your samples.

Sample preparation must be done in your lab, not in the NMR lab.

• Check that the tube is clean and wipe the tube with the provided micro fibre cloth.
• Wash tubes with CH2Cl2 if necessary and dry under vacuum. Do not heat tubes or store them in an oven as it is likely to distort the tube.
• Check that the cap is clean and dry.
• Weigh (roughly) the quantity of sample used . >5-10mg for 1H, 20-50mg for 13C. In most cases 50mg is the maximum that should ever be required. Greater amounts can result in viscous solutions which give poor resolution.
• Sample length should be 5cm long using 0.7ml of solvent. Shorter samples will produce spectra with much poorer resolution. It cause tuning and shimming problems.
• Solid particles, especially those in cloudy solution drastically reduce spectral quality. Do not use large quantities of solvent to dissolve samples, use the minimum volume and filter (either use tissue wrapped round the end of a Pasteur pipette, or filter through a Pasteur pipette plugged with a piece of tissue).

• Length of NMR tubesBroken tubes (i.e. tubes with jagged or fractured ends) are a potential hazard and are not to be used. Please discard these tubes. The bottom of tubes should be regularly checked for hairline cracks. NMR staff will confiscate broken NMR tubes.
  Deformed tubes cause tuning and shimming problems. Many of the cheap disposable tubes are deformed at the bottom, please keep an eye out for this.
• Minimum tube length is 18cm.
• Maximum tube length for the instruments with sample changers is 22cm.
• Young’s tap tubes up to 22cm long can be used.
• If you have longer Young’s taps tubes PLEASE CHECK WITH NMR STAFF FIRST.