Trace analysis by low-field NMR: Breaking the sensitivity limit

Abstract

Sensitivity poses a persistent challenge to NMR spectroscopy and magnetic resonance imaging (MRI). Nonhydrogenative para-hydrogen induced polarization (NH-PHIP) has recently emerged as an efficient method to substantially increase the sensitivity of high-field NMR. Here, we report the feasibility of applying NH-PHIP in the low-field NMR. A trace amount of pyridine of just a few nanoliters (∼12 nmol) in a 0.4 mL NMR sample (a concentration of 31 μM or 1016/cm3) could be measured in a single scan by NH-PHIP. There is a striking difference in the signal-to-noise ratio (SNR) between thermal prepolarization and NH-PHIP: The SNR of the prepolarized 1H NMR signal decreases linearly with decreasing 1H concentration ([1H]) while the SNR in NH-PHIP experiments first increases with decreasing [1H], then remains constant over 2 orders of magnitude, and finally decreases linearly with decreasing [1H]. A hitherto unknown potential opens up for trace analysis by low-field NMR in the bio-, chemical, and material sciences. © 2010 American Chemical Society.