title: 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 ( approximately 12 nmol) in a 0.4 mL NMR sample (a concentration of 31 microM or 10(16)/cm(3)) 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 (1)H NMR signal decreases linearly with decreasing (1)H concentration ([(1)H]) while the SNR in NH-PHIP experiments first increases with decreasing [(1)H], then remains constant over 2 orders of magnitude, and finally decreases linearly with decreasing [(1)H]. A hitherto unknown potential opens up for trace analysis by low-field NMR in the bio-, chemical, and material sciences.
authors.affiliation: Institute of Technical and Macromolecular Chemistry, RWTH Aachen University, 52056 Aachen, Germany.
authors.forename: Qingxia
authors.initials: Q
authors.lastname: Gong
authors.forename: Ali
authors.initials: A
authors.lastname: Gordji-Nejad
authors.forename: Bernhard
authors.initials: B
authors.lastname: Blümich
authors.forename: Stephan
authors.initials: S
authors.lastname: Appelt