If you have a limited amount of sample, you can use 3mm NMR tubes to reduce solvent volume therefore to increase sample concentration (by a factor of 3). You can get 3mm NMR tubes from the Chemistry Storeroom. To use 3mm tubes with 5mm NMR probes equipped on our spectrometers, you’ll need to use a “3mm insert” for 5mm spinners. Ask the NMR staff for the insert.
Another option for a limited amount of sample is to use solvent susceptibility matched NMR tubes (e.g. Shigemi tubes), but they’re expensive.