Sample tubes

 High-field NMR requires the use of sample tubes of accurate dimensions and tubes equivalent to at least Wilmad's 507, or New-Era ML5 or MP5 tubes must be used for research work. The MP5 tubes are available from the chemical stores.

It is important to keep tubes free from dust, grease etc., but they should never be cleaned with chromic acid, as this may leave behind paramagnetic impurities in the glass which makes them unusable. The commercial cleaning agent "Decon-90" is a very effective alternative for removing contamination, especially grease. After soaking in a suitable solution, tubes can be rinsed with distilled water and then acetone. It is, however, surprisingly difficult to free 5 mm tubes from traces of acetone. An effective method is to blow nitrogen or air through the tube, with a pipette, while warming it gently for a few minutes or to leave under vacuum for some hours. If oven drying tubes it is essential that you lay your tubes flat to prevent them from warping, and it is highly recommended that you heat the tubes to no more than 100 oC for one hour at most. Do not subject NMR tubes to high temperatures for long periods of time (this includes oven drying) as this will cause them to distort and become unusable.