Desktop NMR and Its Applications From Materials Science To Organic Chemistry

Abstract

NMR spectroscopy is an indispensable method of analysis in chemistry, which until recently suffered from high demands for space, high costs for acquisition and maintenance, and operational complexity. This has changed with the introduction of compact NMR spectrometers suitable for small-molecule analysis on the chemical workbench. These spectrometers contain permanent magnets giving rise to proton NMR frequencies between 40 and 80 MHz. The enabling technology is to make small permanent magnets with homogeneous fields. Tabletop instruments with inhomogeneous fields have been in use for over 40 years for characterizing food and hydrogen-containing materials by relaxation and diffusion measurements. Related NMR instruments measure these parameters in the stray field outside the magnet. They are used to inspect the borehole walls of oil wells and to test objects nondestructively. The state-of-the-art of NMR spectroscopy, imaging and relaxometry with compact instruments is reviewed.

Benchtop NMR for Online Reaction Monitoring of the Biocatalytic Synthesis of Aromatic Amino Alcohols

“…Recent advances with benchtop NMR (nuclear magnetic resonance) spectroscopy makes online reaction monitoring possible not only for chemical syntheses, but also for fermentation processes, and biocatalytic reactions where low analyte concentrations and the necessity of using deuterated solvents has impeded the use of NMR in the past. A detailed overview of the advantages and disadvantages of benchtop NMR for online reaction monitoring in general can be found in references . With respect to the monitoring of biocatalytic reactions, online NMR offers advantages such as the possibility of analyzing the reaction mixture without destroying or changing the sample composition and without the need for extensive sampling.…”

Application of green analytical chemistry to a green chemistry process: Magnetic resonance and Raman spectroscopic process monitoring of continuous ethanolic fermentation

“…The dimensions of the analyzers should follow an ecological and economical point of view (Pinto, Pereira, Ribeiro, & Farinas, ; Pinto, Ribeiro, & Farinas, ). Compact spectrometers, that is, small‐dimension analyzers, are flexible, robust and today available for a wide range of applications (Blümich, ; Blümich & Singh, ; Danieli et al, ; Kern et al, ; Killner, Garro Linck, Danieli, Rohwedder, & Blümich, ; Kreyenschulte, Paciok, Regestein, Blümich, & Büchs, ; Meyer, Kern, Zientek, Guthausen, & Maiwald, ; Singh, Danieli, & Blümich, ). Automated analyses should be performed preferably without sample preparation and in real time (Maiwald et al, ; Meyer et al, ; Rathore, Bhushan, & Hadpe, ; Rosas, Blanco, González, & Alcalà, ; Singh et al, ; Sugimoto, Fukuyama, Sumino, Takagi, & Ryu, ).…”

Aging of polymeric materials by stray‐field NMR relaxometry with the NMR‐MOUSE

“…[3][4][5] A portable NMR relaxometry sensor for nondestructive testing is the NMR-MOUSE (MObile Universal Surface Explorer), which measures the NMR relaxation from a thin slice within an object exposed to the stray-stray field of a permanent magnet ( Figure 1). [6][7][8][9][10] The sensor is constructed from four permanent magnet blocks placed on an iron yoke with finely adjusted gaps between the magnets, so that the stray-field of the magnet arrangement is parallel to the sensor surface and constant within a thin slice at a fixed distance away from the surface. 11 Depending on the size of the NMR-MOUSE, this slice is located at a distance of 5, 10, or 25 mm from the sensor, and it is 10-100 μm thick with a diameter of 10-25 mm.…”