Low-field benchtop NMR spectroscopy: status and prospects in natural product analysis

Introduction: Since a couple of years, low-field (LF) nuclear magnetic resonance (NMR) spectrometers (40–100 MHz) have re-entered the market. They are used for various purposes including analyses of natural products. Similar to high-field instruments (300–1200 MHz), modern LF instruments can measure multiple nuclei and record two-dimensional (2D) NMR spectra. Objective: To review the commercial availability as well as applications, advantages, limitations, and prospects of LF-NMR spectrometers for the purpose of natural products analysis. Method: Commercial LF instruments were compared. A literature search was performed for articles using and discussing modern LF-NMR. Next, the articles relevant to natural products were read and summarised. Results: Seventy articles were reviewed. Most appeared in 2018 and 2019. Low costs and ease of operation are most often mentioned as reasons for using LF-NMR. Conclusion: As the spectral resolution of LF instruments is limited, they are not used for structure elucidation of new natural products but rather applied for quality control (QC), forensics, food and health research, process control and teaching. Chemometric data handling is valuable. LF-NMR is a rapidly developing niche and new instruments keep being introduced.</p