Proton-enhanced NMR of dilute spins in solids

TLDR

Dilute nuclear spins in solids can be detected with up to a thousand‑fold sensitivity gain by repeatedly transferring polarization from abundant protons. This gain is achieved through double‑resonance polarization transfer and proton decoupling, with experimental requirements and sensitivity compared to other techniques discussed. The method is illustrated by representative applications and experimental results.

Abstract

The NMR signals of isotopically or chemically dilute nuclear spins S in solids can be enhanced by repeatedly transferring polarization from a more abundant species I of high abundance (usually protons) to which they are coupled. The gain in power sensitivity as compared with conventional observation of the rare spins approaches NII(I+1)γI2/NSS(S+1)γS2, or ∼ 103 for S = 13C, I = 1H in organic solids. The transfer of polarization is accomplished by any of a number of double resonance methods. High-frequency resolution of the S -spin signal is obtained by decoupling of the abundant spins. The experimental requirements of the technique are discussed and a brief comparison of its sensitivity with other procedures is made. Representative applications and experimental results are mentioned.