title: Nonlinear detection of secondary isotopic chemical shifts in NMR through spin noise.
abstract: The detection of minor species in the presence of large amounts of similar main components remains a key challenge in analytical chemistry, for instance, to obtain isotopic fingerprints. As an alternative to the classical NMR scheme based on coherent excitation and detection, here we introduce an approach based on spin-noise detection. Chemical shifts and transverse relaxation rates are determined using only the detection circuit. Thanks to a nonlinear effect in mixtures with small chemical shift dispersion, small signals on top of a larger one can be observed with increased sensitivity as bumps on a dip; the latter being the signature of the main magnetization. Experimental observations are underpinned by an analytical theory: the coupling between the magnetization and the coil provides an amplified detection capability of both small static magnetic field inhomogeneities and small NMR signals. This is illustrated by two-bond12C/13C isotopic measurements.
authors.affiliation: Institute of Organic Chemistry, Johannes Kepler University Linz, Altenbergerstraße 69, 4040 Linz, Austria.
authors.forename: Maria Theresia
authors.initials: MT
authors.lastname: Pöschko
authors.affiliation: Institute of Organic Chemistry, Johannes Kepler University Linz, Altenbergerstraße 69, 4040 Linz, Austria.
authors.forename: Victor V
authors.identifier: 0000-0001-6671-1014
authors.initials: VV
authors.lastname: Rodin
authors.affiliation: Institute of Organic Chemistry, Johannes Kepler University Linz, Altenbergerstraße 69, 4040 Linz, Austria.
authors.forename: Judith
authors.initials: J
authors.lastname: Schlagnitweit
authors.affiliation: Institute of Organic Chemistry, Johannes Kepler University Linz, Altenbergerstraße 69, 4040 Linz, Austria.
authors.forename: Norbert
authors.initials: N
authors.lastname: Müller
authors.affiliation: NIMBE, CEA, CNRS, Université Paris-Saclay, CEA/Saclay, 91191 Gif-sur-Yvette, France.
authors.forename: Hervé
authors.initials: H
authors.lastname: Desvaux