Köckenberger, W. and J. Matysik, Hyperpolarization Methods and Applications in NMR, in Encyclopedia of Spectroscopy and Spectrometry (Second Edition), L. Editor-in-Chief: John, Editor. 2010, Academic Press: Oxford. p. 963-970.
Nuclear magnetic resonance (NMR) is a well known and versatile spectroscopic and analytical technique. Its enormous success is due to its capacity to determine structures of molecules and proteins in solutions and amorphous solids, to measure local mobilities, to provide information on reaction mechanisms, and to construct three-dimensional images. The main constraints of NMR are its limitation to microsecond time resolution and the low sensitivity. The latter problem is caused by the weak magnetic properties of nuclei and a resulting unfavorable Boltzmann distribution occurring under equilibrium conditions. Therefore, several methods have been developed to produce non-Boltzmann nuclear spin states leading to hyperpolarization and enhanced sensitivity. These hyperpolarization methods induce spin-chemical processes that overcome the Boltzmann equilibrium of the nuclear spins. Under these conditions, signals enhanced to a factor of more than 10 000 are observed. Hyperpolarization methods use light, microwaves, or chemical reactions and, therefore, link different forms of spectroscopy.