When you cannot use lock solvents

The most common internal locking scheme in high resolution solution NMR is to lock on the deuterium in deuterated solvents and many spectrometer locks are set up only for deuterium. What if the sample does not contain any deuterium (The following argument is true for any nuclei chosen for locking.) An instance of this would be with an air sensitive sample well sealed in a tube and not containing any deuterium. 

An obvious and well used solution to this problem is to use an appropriate deuterium containing solution in the same NMR coil but physically separated from the sample under study. There are two ways to do this. If you have a sealed sample tube which is not to be contaminated, the lock sample must go on the outside of the sample tube. For example, an 8 mm o.d. sample tube fits nicely in a 10 mm o.d. tube with just enough room for an annulus of lock solution. 

A better scheme, if the sample can be opened to air, is to use a capillary containing the lock material in the center of the sample tube. This scheme is better in the sense that you do not need as much locking material so that the signal S/N can be better than in the annulus scheme. In both schemes, it is important to engineer precision spacers so the cylindrical 

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