NMR Tubes Information
An NMR tube is a thin glass walled tube used to contain samples in nuclear magnetic resonance spectroscopy. Typically NMR tubes come in 5 mm diameters but can also range from 10 mm to 3 mm samples. It is important that the tubes are uniformly thick and well-balanced to ensure that NMR tube spins at a regular rate (i.e. that they do not wobble), usually about 20 Hz in an NMR spectrometer.
NMR tubes are available in quartz or borosilicate. There is typically a large cost difference between choosing one material over another with quartz being the more expensive option. Quartz is available in two grades: fused and synthetic. The purity of quartz is better controlled and can be heated and cooled faster and has a lower UV cutoff of 190 nm opposed to 320 nm. Quartz NMR tubes are also better geometrically controlled than your typical borosilicate allowing for better balance within the NMR spectrometer. There are different grades of borosilicate, such as the high-quality Pyrex or the lower-quality Class B, each comes with its own limitations.
Inexpensive tubes will often have widely varying wall thickness or a pronounced bend, making spinning more difficult. More expensive tubes do not guarantee results, but merely reduce the chances of error or failure due to the tube itself.
Three more important parameters to consider are concentricity, camber, and wall thickness. Lower quality tubes will tend to have less precision and as a result your sample may wobble while spinning.