RESEARCH ARTICLE A table‐top PXI based low‐field spectrometer for solution dynamic nuclear polarization Joshua R. Biller | Karl F. Stupic | J. Moreland Physical Measurement Laboratory, National Institute of Standards and Technology, Boulder, CO, USA Correspondence Joshua R. Biller, Physical Measurement Laboratory, National Institute of Standards and Technology, 325 Broadway, Boulder, CO 80305, USA. Email: joshua.biller@nist.gov We present the development of a portable dynamic nuclear polarization (DNP) instrument based on the PCI eXtensions for Instrumentation platform. The main purpose of the instrument is for study of 1 H polarization enhancements in solution through the Overhauser mechanism at low magnetic fields. A DNP probe set was constructed for use at 6.7 mT, using a modified Alder- man–Grant resonator at 241 MHz for saturation of the electron transition. The solenoid for detection of the enhanced 1 H signal at 288 kHz was con- structed with Litz wire. The largest observed 1 H enhancements (ε) at 6.7 mT for 14 N‐CTPO radical in air saturated aqueous solution was ε~65. A concentra- tion dependence of the enhancement is observed, with maximum ε at 5.5 mM. A low resonator efficiency for saturation of the electron paramagnetic resonance transition results in a decrease in ε for the 10.3 mM sample. At high incident powers (42 W) and long pump times, capacitor heating effects can also decrease the enhancement. The core unit and program described here could be easily adopted for multi‐frequency DNP work, depending on available main magnets and selection of the “plug and play” arbitrary waveform generator, digitizer, and radiofrequency synthesizer PCI eXtensions for Instrumentatione cards. KEYWORDS 1H, DNP, Hyperpolarization, LabVIEW, Nitroxide, PXI, Resonator efficiency 1 | INTRODUCTION Dynamic nuclear polarization (DNP) is a technique for enhancing the polarization of nuclear spins in the vicinity of unpaired electrons. The mechanisms which determine the magnitude of enhancement vary. At high magnetic fields and in the solid state, the enhancement is described by considering the number of interacting spins contribut- ing to the enhancement: two spins (solid effect [1–4] ), three spins (cross effect [5,6] ) or multiple spins (thermal effect [7] ). In solution, the molecule containing the unpaired elec- tron and the proton are tumbling rapidly, and enhance- ment is determined by the Overhauser effect (OE). The magnitude of the OE is dependent on the time scale mod- ulating the interaction between electron and nuclear spins and the distance of closest approach. The OE is the longest studied DNP mechanism, going back over 60 years to the first experimental demonstrations. [8,9] The general expression for the enhancement (ε) is given by Equation 1 ε ¼ 1−ρsf γ S γ I         (1) Contribution of the National Institute of Standards and Technology; not subject to copyright in the United States.Certain commercial instru- ments and software are identified to specify the experimental study ade- quately. This does not imply endorsement by NIST or that the instruments and software are the best available for the purpose. Received: 22 August 2017 Revised: 29 September 2017 Accepted: 4 October 2017 DOI: 10.1002/mrc.4672 Magn Reson Chem. 2017;1–11. Published 2017. This article is a U.S. Government work and is in the public domain in the USA. wileyonlinelibrary.com/journal/mrc 1