Mar 20, 2019 – NMR Topical Group Meeting

Nuclear magnetic resonance (NMR) is a powerful tool for quantitative molecular analysis. While high-field NMR spectrometers are based on bulky superconducting magnets, several low-field NMR instruments (based on permanent magnets) have been developed as robust, mobile, low-cost alternatives. The vast majority of low-field NMR instruments are limited to 1H experiments sometimes combined with a narrowband channel for another high-sensitive isotope. However, practical applications of NMR exist for a large variety of detection isotopes.

To utilize this potential, we have developed a cost-efficient, benchtop/on-line NMR instrument with a broadband channel covering the frequencies of all relevant NMR-active isotopes with fast digital tune/match capability. The Tveskaeg NMR instrument (NanoNord A/S, Denmark) is based on a ~1.5 T permanent Halbach magnet, a digital console, and a probe with 2 ml sensitive sample volume (i.d. 9.2 mm). The instrument is suitable for use in laboratories, for fieldwork, and in on-line setups for continuous monitoring applications.

Targeting specific industrial applications, we have conducted a variety of studies to demonstrate the performance of the NMR instrumentation in the laboratory and at industrial positions of use. Some of these applications are: (i) On-line monitoring of catalytic fines in heavy fuel oil onboard ships using 27Al NMR. (ii) Continuous monitoring of ammonium, phosphorus and chloride levels at wastewater treatment plants by 14N, 31P and 35Cl NMR. (iii) Quantification of nutrients in agricultural manure by 14N, 17O, 31P and 39K NMR. (iv) Quantification of salt in food products by 23Na and 35Cl NMR. (v) Quantification of protein and fat contents in milk. (vi) Monitoring of boron and lithium in reactor coolant at power plants by 11B, 10B and 7Li NMR.

Furthermore, the benchtop instrument is an efficient spectrometer for wide-line solid-state NMR experiments. The is demonstrated experimentally by acquisition of challenging spectra like the 14N spectrum of KNO3 spanning more than 1 MHz. By introducing interleaved sampling of frequency slices, a highly efficient acquisition is achievable with a sensitivity comparable to high-field NMR experiments.

Overall, our results demonstrate some of the capabilities and the versatility using multinuclear, cost-efficient NMR as a robust analytical tool suitable for both scientific and large-scale industrial applications.