Category Archives: Instrumentation

Magnets for Small-Scale and Portable NMR

Blümich, Bernhard, Christian Rehorn, and Wasif Zia. “Magnets for Small-Scale and Portable NMR.” In Micro and Nano Scale NMR, by Jens Anders and Jan G. Korvink, 1–20. Advanced Micro and Nanosystems. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA, 2018.

https://doi.org/10.1002/9783527697281.ch1.

Nuclear magnetic resonance (NMR) exploits the resonance of the precessing motion of nuclear magnetization in magnetic fields. From the measurement methodology, three groups of common techniques of probing resonance can be assigned: those employing forced oscillations, free oscillations, and interferometric principles. In either case, the sensitivity depends on the strength of the nuclear magnetic polarization, which, in thermodynamic equilibrium at temperatures higher than few degrees above absolute zero, is in good approximation proportional to the strength of the magnetic field. In recognition of this fact, one guideline in the development of NMR magnets has always been to reach high field strength.The highest field strength of temporally stable magnetic fields today is achieved with superconducting electromagnets. This is why most standard NMR instruments used for NMR spectroscopy in chemical analysis and magnetic resonance imaging (MRI) in medical diagnostics employ superconducting magnets cooled to the low temperature of boiling helium with cryogenic technology.

Microcoils for Broadband Multinuclei Detection

Anders, Jens, and Aldrik H. Velders. “Microcoils for Broadband Multinuclei Detection.” In Micro and Nano Scale NMR, by Jens Anders and Jan G. Korvink, 265–96. Advanced Micro and Nanosystems. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA, 2018.

https://doi.org/10.1002/9783527697281.ch10.

NMR techniques are among the most influential analytical tools developed in the past century and widely used in various disciplines from oil well drilling to medicine. To date, two major hurdles inhibit an even more widespread use of NMR spectroscopy in science and society: first, NMR’s relatively low sensitivity severely constrains applications of mass- and volume-limited samples including lab-on-chip integration, in-cell analysis, and bioanalyte detection. Typical NMR samples contain micromole quantities of material in a relatively large sample volume of about 0.5ml; this large sample volume in turn imposes stringent requirements on the magnetic field – both for the generation but also on the susceptibility of the materials utilized in the probe head – which has to be homogenous in the whole sample volume with ppb resolution. Second, NMR equipment is very complex and costly. A major contribution to the high price of NMR equipment is constituted by the (cryogenic) superconducting magnets used to generate the static magnetic field.This problem will hopefully be tackled by the introduction of new magnet-manufacturing techniques and materials, for example, high-temperature superconductors, and the development of miniaturized spectrometers. Another complex and costly aspect concerns the heart of spectrometers consisting of intricate multifrequency probes, with coils integrated in sophisticated tuning–matching circuits connected to complex RF transceiver circuits. In viewof these limitations of currentNMRsystems, to make NMR more versatile and affordable, a key challenge is improving sensitivity and, at the same time, reducing cost and complexity of NMR probes and electronics.

Field Guide to Terahertz Sources, Detectors, and Optics

I recently came across this very handy and useful publication. It is helpful to anyone who wants to understand the design of quasi-optical elements, which are for example used in many high-field EPR spectrometers.

O’Sullivan, Créidhe M., and J. Anthony Murphy. Field Guide to Terahertz Sources, Detectors, and Optics. SPIE, 2012.

https://doi.org/10.1117/3.952851.

The region of the electromagnetic spectrum between microwaves and infrared radiation has come to be known as the “THz gap,” mainly due to the lack of readily available laboratory sources and detectors. For many years technology development was driven by astronomers and planetary scientists, but other potential uses, particularly in medical and security applications, have led to increased activity by the mainstream physics and engineering community in recent times. Because diffraction is important at these frequencies, THz systems cannot be successfully designed using traditional optical techniques alone.

The primary objective of this Field Guide is to provide the reader with a concise description of the quasi-optical techniques used at THz frequencies, as well as the basic principles of operation of the most common THz system components in use today. More detailed accounts of specific devices can be found in the bibliography and references therein.

Wave Guides for Micromagnetic Resonance

Yilmaz, Ali, and Marcel Utz. “Wave Guides for Micromagnetic Resonance.” In Micro and Nano Scale NMR, by Jens Anders and Jan G. Korvink, 75–108. Advanced Micro and Nanosystems. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA, 2018.

https://doi.org/10.1002/9783527697281.ch4.

In nuclear magnetic resonance, a system of nuclear spins exposed to a static magnetic interacts with an oscillatory field, usually in the radio frequency range. In most NMR setups, including all commercially available NMR spectrometers, coherent transitions between spin states are detected by a voltage induced into a conductor surrounding the sample. Whereas other detection techniques have their advantages in certain cases, inductive detection has proven to be both robust and easy to implement.

A method for fast field settling in cryogen-free superconducting magnets for NMR

Cryogen-free magnets are around for EPR spectroscopy for a while already, however, in recent years they also become more popular for NMR spectroscopy (solids and solutions). This article greatly demonstrate the potential of the technology.

Kryukov, Eugeny, Yury Bugoslavsky, Angel Joaquin Perez Linde, Thomas Holubar, Stephen Burgess, David Marlow, and Jeremy Good. “A Method for Fast Field Settling in Cryogen-Free Superconducting Magnets for NMR.” Solid State Nuclear Magnetic Resonance 109 (October 2020): 101684.

https://doi.org/10.1016/j.ssnmr.2020.101684.

We propose a fast algorithm to energise a cryogen free magnet to a highly persistent state. A decay rate as low as 0.021 ppm/h can be achieved in less than an hour after reaching the target field. The decay rate drops further to 0.0004 ppm/h in the following 48 h. This procedure can be applied at different values of target field, which makes it feasible to use a single magnet for study of various NMR lines at different fields. The mechanism of establishing a highly stable magnetic field can be understood on the basis of the magnetic properties of the superconducting wire, which were studied using a vibrating sample magnetometer. The results confirm the high quality of the superconducting wire and joints.

XeUS: A second-generation automated open-source batch-mode clinical-scale hyperpolarizer

Birchall, Jonathan R., Robert K. Irwin, Panayiotis Nikolaou, Aaron M. Coffey, Bryce E. Kidd, Megan Murphy, Michael Molway, et al. “XeUS: A Second-Generation Automated Open-Source Batch-Mode Clinical-Scale Hyperpolarizer.” Journal of Magnetic Resonance 319 (October 2020): 106813.

https://doi.org/10.1016/j.jmr.2020.106813.

We present a second-generation open-source automated batch-mode 129Xe hyperpolarizer (XeUS GEN2), designed for clinical-scale hyperpolarized (HP) 129Xe production via spin-exchange optical pumping (SEOP) in the regimes of high Xe density (0.66–2.5 atm partial pressure) and resonant photon flux (~170 W, Dk = 0.154 nm FWHM), without the need for cryo-collection typically employed by continuous-flow hyperpolarizers. An Arduino micro-controller was used for hyperpolarizer operation. Processing open-source software was employed to program a custom graphical user interface (GUI), capable of remote automation. The Arduino Integrated Development Environment (IDE) was used to design a variety of customized automation sequences such as temperature ramping, NMR signal acquisition, and SEOP cell refilling for increased reliability. A polycarbonate 3D-printed oven equipped with a thermoelectric cooler/heater provides thermal stability for SEOP for both binary (Xe/N2) and ternary (4He-containing) SEOP cell gas mixtures. Quantitative studies of the 129Xe hyperpolarization process demonstrate that near-unity polarization can be achieved in a 0.5 L SEOP cell. For example, %PXe of 93.2 ± 2.9% is achieved at 0.66 atm Xe pressure with polarization build-up rate constant cSEOP = 0.040 ± 0.005 minÀ1, giving a max dose equivalent % 0.11 L/h 100% hyperpolarized, 100% enriched 129Xe; %PXe of 72.6 ± 1.4% is achieved at 1.75 atm Xe pressure with cSEOP of 0.041 ± 0.001 minÀ1, yielding a corresponding max dose equivalent of 0.27 L/h. Quality assurance studies on this device have demonstrated the potential to refill SEOP cells hundreds of times without significant losses in performance, with average %PXe = 71.7%, (standard deviation rP = 1.52%) and mean polarization lifetime T1 = 90.5 min, (standard deviation rT = 10.3 min) over the first ~200 gas mixture refills, with sufficient performance maintained across a further ~700 refills. These findings highlight numerous technological developments and have significant translational relevance for efficient production of gaseous HP 129Xe contrast agents for use in clinical imaging and bio-sensing techniques.

A temperature-controlled sample shuttle for field-cycling NMR

Today, something that has nothing to do with DNP-NMR spectroscopy, but is a cool piece of equipment.

Hall, Andrew M.R., Topaz A.A. Cartlidge, and Giuseppe Pileio. “A Temperature-Controlled Sample Shuttle for Field-Cycling NMR.” Journal of Magnetic Resonance 317 (August 2020): 106778. https://doi.org/10.1016/j.jmr.2020.106778

We present a design for a temperature-controlled sample shuttle for use in NMR measurements at variable magnetic field strength. Accurate temperature control was achieved using a mixture of waterethylene glycol as a heat transfer fluid, reducing temperature gradients across the sample to <0.05 °C and minimising convection. Using the sample shuttle, we show how the longitudinal (T1) and singlet order (TS) relaxation time constants were measured for two molecules capable of supporting long-lived states, with new record lifetimes observed at low field and above ambient temperatures.

Organic Reaction Monitoring of a Glycine Derivative Using Signal Amplification by Reversible Exchange-Hyperpolarized Benchtop Nuclear Magnetic Resonance Spectroscopy #DNPNMR #SABRE

Chae, Heelim, Sein Min, Hye Jin Jeong, Sung Keon Namgoong, Sangwon Oh, Kiwoong Kim, and Keunhong Jeong. “Organic Reaction Monitoring of a Glycine Derivative Using Signal Amplification by Reversible Exchange-Hyperpolarized Benchtop Nuclear Magnetic Resonance Spectroscopy.” Analytical Chemistry 92, no. 16 (August 18, 2020): 10902–7.

https://doi.org/10.1021/acs.analchem.0c01270

Currently, signal amplification by reversible exchange (SABRE) using para-hydrogen is an attractive method of hyperpolarization for overcoming the sensitivity problems of nuclear magnetic resonance (NMR) spectroscopy. Additionally, SABRE, using the spin order of para-hydrogen, can be applied in reaction monitoring processes for organic chemistry reactions where a small amount of reactant exists. The organic reaction monitoring system created by integrating SABRE and benchtop NMR is the ideal combination for monitoring a reaction and identifying the small amounts of materials in the middle of the reaction. We used a laboratory-built setup, prepared materials by synthesis, and showed that the products obtained by esterification of glycine were also active in SABRE. The products, which were synthesized esterified glycine with nicotinoyl chloride hydrochloride, were observed with a reaction monitoring system. The maximum SABRE enhancement among them (approximately 147-fold) validated the use of this method. This study is the first example of the monitoring of this organic reaction by SABRE and benchtop NMR. It will open new possibilities for applying this system to many other organic reactions and also provide more fruitful future applications such as drug discovery and mechanism study.

A compact X-Band ODNP spectrometer towards hyperpolarized 1H spectroscopy #DNPNMR #ODNP

Überrück, Till, Michael Adams, Josef Granwehr, and Bernhard Blümich. “A Compact X-Band ODNP Spectrometer towards Hyperpolarized 1H Spectroscopy.” Journal of Magnetic Resonance, April 2020, 106724.

https://doi.org/10.1016/j.jmr.2020.106724

The demand for compact benchtop NMR systems that can resolve chemical shift differences in the ppm to sub-ppm range is growing. However due to material and size restrictions these magnets are limited in field strength and thus in signal intensity and quality. The implementation of standard hyperpolarization techniques is a next step in an effort to boost the signal. Here we present a compact Overhauser Dynamic Nuclear Polarization (ODNP) setup with a permanent magnet that can resolve 1H chemical shift differences in the ppm range. The assembly of the setup and its components are described in detail, and the functionality of the setup is demonstrated experimentally with ODNP enhanced relaxation measurements yielding a maximal enhancement of -140 for an aqueous 4Hydroxy-TEMPO solution. Additionally, 1H spectroscopic resolution and significant enhancements are demonstrated on acetic acid as a solvent.

Inductance Calculation in Magnetic Resonance Solenoid Coils with Strip and Wire Conductors #Instrumentation #NMR

If you’ve ever built your own RF circuit for NMR you know that calculating the inductance for a solenoid can be challenging. This article gives some insight where the discrepancies are coming from and how to make the prediction more accurately. However, in the end you still need to get the soldering iron out and adjust capacitors to make it work.

Giovannetti, Giulio, and Francesca Frijia. “Inductance Calculation in Magnetic Resonance Solenoid Coils with Strip and Wire Conductors.” Applied Magnetic Resonance 51, no. 8 (August 2020): 703–10.

https://doi.org/10.1007/s00723-020-01230-0

Solenoids are employed in Magnetic Resonance (MR) as radiofrequency (RF) coils due to their high sensitivity. In particular, their cylindrical symmetry is optimal for circular cross-sectional samples. Solenoid inductance estimation is a constraint for a correct design and tuning of the resonant circuit constituting the RF coil, suitable to be used for transmitting and receiving the RF signal of the given X-nucleus with the available MR scanner. However, the different literature formulation for solenoid inductance estimation is not optimized for a wide variety of coil geometries and doesn’t take into account conductor geometry. This paper proposes an analytical method for the solenoid inductance calculation in dependence on the conductor cross-sectional geometry (flat strip and circular wire). Simulations accuracy was evaluated with workbench experimental measurement performed on a home-built strip solenoid and by comparisons with literature data referred to wire solenoids.

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