Wilmad® External Reference System, model 516-CC-5 is manufactured by SP Industries. This product is ideal for separating reference solutions from samples and provides additional protection for toxic samples in NMR spectra. Each insert is precisely inserted into the outer tube. The flat bottom forces the reference solution to move up between the inner and outer tubes. It is easy to use, just put the sample in the insert and add a few drops of reference solution to the bottom of the outer tube. When the inner tube is pushed down, the reference solution is pushed upward and a film of about 50 μ L is formed between the two tubes.