Category Archives: Instrumentation

A large sample volume magic angle spinning nuclear magnetic resonance probe for in situ investigations with constant flow of reactants

This post is not particular about DNP. However, it is a very interesting piece of instrumentation that demonstrates the state-of-the-art of instrumentation for MAS-NMR.

Hu, J.Z., et al., A large sample volume magic angle spinning nuclear magnetic resonance probe for in situ investigations with constant flow of reactants. Phys. Chem. Chem. Phys., 2012. 14(7): p. 2137-2143.

http://dx.doi.org/10.1039/C1CP22692D

A large-sample-volume constant-flow magic angle sample spinning (CF-MAS) NMR probe is reported for in situ studies of the reaction dynamics, stable intermediates/transition states, and mechanisms of catalytic reactions. In our approach, the reactants are introduced into the catalyst bed using a fixed tube at one end of the MAS rotor while a second fixed tube, linked to a vacuum pump, is attached at the other end of the rotor. The pressure difference between both ends of the catalyst bed inside the sample cell space forces the reactants flowing through the catalyst bed, which improves the diffusion of the reactants and products. This design allows the use of a large sample volume for enhanced sensitivity and thus permitting in situ13C CF-MAS studies at natural abundance. As an example of application, we show that reactants, products and reaction transition states associated with the 2-butanol dehydration reaction over a mesoporous silicalite supported heteropoly acid catalyst (HPA/meso-silicalite-1) can all be detected in a single 13C CF-MAS NMR spectrum at natural abundance. Coke products can also be detected at natural 13C abundance and under the stopped flow condition. Furthermore, 1H CF-MAS NMR is used to identify the surface functional groups of HPA/meso-silicalite-1 under the condition of in situ drying. We also show that the reaction dynamics of 2-butanol dehydration using HPA/meso-silicalite-1 as a catalyst can be explored using 1H CF-MAS NMR.

A large sample volume magic angle spinning nuclear magnetic resonance probe for in situ investigations with constant flow of reactants

This post is not particular about DNP. However, it is a very interesting piece of instrumentation that demonstrates the state-of-the-art of instrumentation for MAS-NMR.

Hu, J.Z., et al., A large sample volume magic angle spinning nuclear magnetic resonance probe for in situ investigations with constant flow of reactants. Phys. Chem. Chem. Phys., 2012. 14(7): p. 2137-2143.

http://dx.doi.org/10.1039/C1CP22692D

A large-sample-volume constant-flow magic angle sample spinning (CF-MAS) NMR probe is reported for in situ studies of the reaction dynamics, stable intermediates/transition states, and mechanisms of catalytic reactions. In our approach, the reactants are introduced into the catalyst bed using a fixed tube at one end of the MAS rotor while a second fixed tube, linked to a vacuum pump, is attached at the other end of the rotor. The pressure difference between both ends of the catalyst bed inside the sample cell space forces the reactants flowing through the catalyst bed, which improves the diffusion of the reactants and products. This design allows the use of a large sample volume for enhanced sensitivity and thus permitting in situ13C CF-MAS studies at natural abundance. As an example of application, we show that reactants, products and reaction transition states associated with the 2-butanol dehydration reaction over a mesoporous silicalite supported heteropoly acid catalyst (HPA/meso-silicalite-1) can all be detected in a single 13C CF-MAS NMR spectrum at natural abundance. Coke products can also be detected at natural 13C abundance and under the stopped flow condition. Furthermore, 1H CF-MAS NMR is used to identify the surface functional groups of HPA/meso-silicalite-1 under the condition of in situ drying. We also show that the reaction dynamics of 2-butanol dehydration using HPA/meso-silicalite-1 as a catalyst can be explored using 1H CF-MAS NMR.

Dynamic nuclear polarization at 9T using a novel 250 Gyrotron microwave source

Griffin, R. G. J. Magn. Reson. 2011, 213, 410

http://dx.doi.org/10.1016/j.jmr.2011.08.015

In the 1990\’s we initiated development of high frequency gyrotron microwave sources with the goal of performing dynamic nuclear polarization at magnetic fields (~5-23T) used in contemporary NMR experiments. This article describes the motivation for these efforts and the developments that led to the operation of a gyrotron source for DNP operating at 250 GHz. We also mention results obtained with this instrument that would have been otherwise impossible absent the increased sensitivity. Finally, we describe recent efforts that have extended DNP to 460 GHz and 700 MHz 1H frequencies.

Dynamic nuclear polarization at 9T using a novel 250 Gyrotron microwave source

Griffin, R. G. J. Magn. Reson. 2011, 213, 410

http://dx.doi.org/10.1016/j.jmr.2011.08.015

In the 1990\’s we initiated development of high frequency gyrotron microwave sources with the goal of performing dynamic nuclear polarization at magnetic fields (~5-23T) used in contemporary NMR experiments. This article describes the motivation for these efforts and the developments that led to the operation of a gyrotron source for DNP operating at 250 GHz. We also mention results obtained with this instrument that would have been otherwise impossible absent the increased sensitivity. Finally, we describe recent efforts that have extended DNP to 460 GHz and 700 MHz 1H frequencies.

Stacked rings for terahertz wave-guiding

de Rijk, E.; Macor, A.; Hogge, J.; Alberti, S.; Ansermet, J. Review of Scientific Instruments 2011, 82, 066102.

http://dx.doi.org/10.1063/1.3597579

We demonstrate the construction of corrugated waveguides using stacked rings to propagate terahertz frequencies. The waveguide allows propagation of the same fundamental mode as an optical-fiber, namely, the HE11 mode. This simple concept opens the way for corrugated wave-guides up to several terahertz, maintaining beam characteristics as for terahertz applications.

Stacked rings for terahertz wave-guiding

de Rijk, E.; Macor, A.; Hogge, J.; Alberti, S.; Ansermet, J. Review of Scientific Instruments 2011, 82, 066102.

http://dx.doi.org/10.1063/1.3597579

We demonstrate the construction of corrugated waveguides using stacked rings to propagate terahertz frequencies. The waveguide allows propagation of the same fundamental mode as an optical-fiber, namely, the HE11 mode. This simple concept opens the way for corrugated wave-guides up to several terahertz, maintaining beam characteristics as for terahertz applications.

Operation of a Continuously Frequency-Tunable Second-Harmonic CW 330-GHz Gyrotron for Dynamic Nuclear Polarization

Torrezan, A.C., et al., Operation of a Continuously Frequency-Tunable Second-Harmonic CW 330-GHz Gyrotron for Dynamic Nuclear Polarization. IEEE Transactions on Electron Devices, 2011. 58(8): p. 2777-83.

http://dx.doi.org/10.1109/TED.2011.2148721

The design and the operation of a frequency-tunable continuous-wave (CW) 330-GHz gyrotron oscillator operating at the second harmonic of the electron cyclotron frequency are reported. The gyrotron has generated 18 W of power from a 10.1 kV 190 mA electron beam working in a TE-4,3 cylindrical mode, corresponding to an efficiency of 0.9 %. The measured start oscillation current over a range of magnetic field values is in good agreement with theoretical start currents obtained from linear theory for successive high-order axial modes TE-4,3,q, where q = 1-6. Moreover, the observed frequency range in the start current measurement is in reasonable agreement with the frequency range obtained from numerical simulations. The minimum start current was measured to be 33 mA. A continuous tuning range of 1.2 GHz was experimentally observed via a combination of magnetic, voltage, and thermal tuning. The gyrotron output power and frequency stabilities were assessed to be 0.4% and 3 ppm, respectively, during a 110-h uninterrupted CW run. Evaluation of the gyrotron output microwave beam pattern using a pyroelectric camera indicated a Gaussian-like mode content of 92% with an ellipticity of 28%. The gyrotron will be used for 500-MHz nuclear magnetic resonance experiments with sensitivity enhanced by dynamic nuclear polarization.

Operation of a Continuously Frequency-Tunable Second-Harmonic CW 330-GHz Gyrotron for Dynamic Nuclear Polarization

Torrezan, A.C., et al., Operation of a Continuously Frequency-Tunable Second-Harmonic CW 330-GHz Gyrotron for Dynamic Nuclear Polarization. IEEE Transactions on Electron Devices, 2011. 58(8): p. 2777-83.

http://dx.doi.org/10.1109/TED.2011.2148721

The design and the operation of a frequency-tunable continuous-wave (CW) 330-GHz gyrotron oscillator operating at the second harmonic of the electron cyclotron frequency are reported. The gyrotron has generated 18 W of power from a 10.1 kV 190 mA electron beam working in a TE-4,3 cylindrical mode, corresponding to an efficiency of 0.9 %. The measured start oscillation current over a range of magnetic field values is in good agreement with theoretical start currents obtained from linear theory for successive high-order axial modes TE-4,3,q, where q = 1-6. Moreover, the observed frequency range in the start current measurement is in reasonable agreement with the frequency range obtained from numerical simulations. The minimum start current was measured to be 33 mA. A continuous tuning range of 1.2 GHz was experimentally observed via a combination of magnetic, voltage, and thermal tuning. The gyrotron output power and frequency stabilities were assessed to be 0.4% and 3 ppm, respectively, during a 110-h uninterrupted CW run. Evaluation of the gyrotron output microwave beam pattern using a pyroelectric camera indicated a Gaussian-like mode content of 92% with an ellipticity of 28%. The gyrotron will be used for 500-MHz nuclear magnetic resonance experiments with sensitivity enhanced by dynamic nuclear polarization.

Have a question?

If you have questions about our instrumentation or how we can help you, please contact us.