Invited Speaker Australian & New Zealand Society of Magnetic Resonance Conference 2017

DNP-FFC: Improving sensitivity and selectivity in field-cycling relaxometry studies (#71)

Siegfried Stapf 1 , Bulat Gizatullin 1 , Oliver Neudert 1 , Carlos Mattea 1
  1. TU Ilmenau, Ilmenau, THURINGIA, Germany

Dynamic Nuclear Magnetization (DNP) is becoming established for a number of applications in spectroscopy and imaging. It does, however, also offer solutions where signal intensity is critical, such as in low-field and field-cycling studies, where it may open up new possibilities for investigations of polymers, proteins and X nuclei.

This work is part of an ongoing study to verify the feasibility of DNP-FFC. To this end, two DNP units have been constructed that fit into existing FFC hardware, combining electron microwave irradiation at S and X bands, respectively, with subsequent NMR detection [1,2]. Employing DNP-FFC for routine applications involves solving three problem complexes: minimizing sample heating; identifying and describing the magnetization transfer mechanism; and quantifying additional relaxation contributions due to the presence of radicals.

The temperature increase due to microwave irradiation is directly correlated with the quality factor of the probe; this regularly limits the microwave power to several Watts but still generates substantial enhancement factors.

Secondly, Overhauser effect (OE), Solid effect (SE) and Cross effect (CE) have been identified as relevant contributions for most systems except low-viscosity liquids. Singling out the effects requires to scan the entire field dependence of DNP enhancement by varying the polarization field at constant microwave frequency prior to executing the relaxation field switch sequence. With this approach, it was possible to separate multicomponent systems by the simultaneous presence of OE and SE [3,4].

Thirdly, the absence of additional relaxation rates due to the presence of radicals or microwave radiation could be shown for a number of systems, while some low-viscosity liquids featured substantial distortion to their bulk thermal magnetization relaxation dispersion.

DNP-FFC, both at constant and variable relaxation fields, is demonstrated for systems with artificially added radicals such as polymer solutions [5], and for systems naturally containing radicals such as crude oil [6,7].

  1. [1] O. Neudert, H.-P. Raich, C. Mattea, S. Stapf, K. Münnemann, J. Magn. Reson. 242, 79-85 (2014).
  2. [2] O. Neudert, C. Mattea, S. Stapf, J. Magn. Reson.271, 7-14 (2016).
  3. [3] O. Neudert, C. Mattea, H.W. Spieß, S. Stapf, K. Münnemann, Phys. Chem. Chem. Phys. 15, 20717-20726 (2013).
  4. [4] O. Neudert, C. Mattea, S. Stapf, J. Magn. Reson. 276, 113-121 (2017).
  5. [5] B. Gizatullin, O. Neudert, S. Stapf, C. Mattea, ChemPhysChem, in press
  6. [6] O. Neudert, C. Mattea, S. Stapf, M. Reh, H.W. Spieß, K. Münnemann, Microporous Mesoporous Mater. 205, 70-74 (2015).
  7. [7] A. Ordikhani-Seyedlar, O. Neudert, S. Stapf, C. Mattea, R. Kausik, D. E. Freed, Y.-Q. Song, M. D. Hürlimann, Energy Fuels 30, 3886-3893 (2016).