NMR Facility

Department of Chemistry University of Oxford

When preparing solutions for NMR spectroscopy, care should be taken to ensure cleanliness of apparatus and absence of contamination by solvent impurities. A common mistake made by new research workers is to use solvents such as petrol for chromatography or crystallisation without prior purification. Nearly all commercial solvents contain involatile impurities which are insignificant when working with multi-gram quantities of compound, but become very objectionable when working on the small scale quantities high-field NMR has made possible. If you are surprised by giant peaks around 0.5-1.5 ppm (hydrocarbons) or around 0.1 ppm (silicone grease, which always seems to work its way off ground glass joints and into NMR samples), then reconsider your experimental procedures. Distil solvents, avoid vacuum grease, crystallise solids where possible (if you get large, impressive crystals, powder them up and pump on them for a few hours to remove the quantities of solvent trapped inside the crystals) and you should obtain beautiful spectra! When you have dissolved your sample, always filter the solution through a plug of cotton wool straight into the NMR tube to remove any particulate matter. Lack of solid particles is an essential requirement for obtaining high-quality spectra. Samples that are of insufficient quality will be returned for clean-up and must be resubmitted to the service. Clearly, this will lead to delays in obtaining your spectrum, so it is in your best interest to submit a particle free sample.