If sample spinning creates vortexes in your samples, then vortex plugs are the recommended solution. There are a variety of vortex plugs available and this report explains the appropriate use of each type of vortex plug. The tables at the end of the report summarize the advantages and disadvantages of the various vortex plugs and closures available for Wilmad NMR tubes. NMR Tube Caps Wilmad's standard NMR tubes are delivered with a disposable Ethylene Vinyl Acetate cap. Low-cost replacements make it more practical to cut these caps from your NMR tubes at the end of your experiment than risk breaking the tube pulling the cap from the sample tube.
Disposable caps are easy to use.
Careful application helps prevent spinning instability that results when the cap isn't straight. But, because Chloroform can leach unreacted monomers from these caps into your sample, you should replace these disposable caps with Wilmad's WG-1264 series Teflon NMR tube caps when using CDCl 3 . Wilmad's 5mm tube cap 521-PC is Polyethylene and molded with ribs on the inner surface that help the cap grip a 5mm tube. The size and tapered shape of this cap are such that only the lower rib of the cap fits over the tube. This is sufficient to make a firm fit, but the 521-PC does not provide as effective a vapor seal as the disposable caps supplied with Wilmad NMR tubes.