Nuclear magnetic resonance (NMR) spectroscopy, perhaps the most important method for determining the structure of covalently built (mostly organic) compounds, is a non-destructive method of analysis; here, unlike in MS, the analyte can be recovered afterwards,—which is of course quite desirable, especially in the case of a preparatively labourious substance, which you may have synthesised only on a milligram scale and of which you now want to know whether you have really obtained what you were after. (Whether this is always feasible in practice, however, is another matter, because some analytes can only be dissolved in solvents such as dimethyl sulfoxide (DMSO, (CH3)2SO), and the attempt to separate this solvent by distillation is quite questionable in view of its boiling point (bp = 189 °C); there are not too many organic analytes that can withstand such thermal stress ....)