Low‐field benchtop NMR spectroscopy: status and prospects in natural product analysis^†

Abstract

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.

Applications of Non-invasive and Novel Methods of Low-Field Nuclear Magnetic Resonance and Magnetic Resonance Imaging in Aquatic Products

“…It can qualitatively and quantitatively analyze the composition and structure of organic and inorganic materials (15). NMR can be used to analyze the behavior of NMR-active nuclei (i.e., 1 H and 13 C, which are most commonly used for food and processed product applications) (16) in a magnetic field or exposed to pulsed radiofrequency (RF) irradiation (17). Relaxation is the complicated process whereby nuclei transition from an excited state [owing to the splitting of the nuclear spin levels (Zeeman effect) of an applied magnetic field] to equilibrium (18).…”

Jasminum grandiflorum flowers—Phytochemical complexity and its capture in extracts: a review

“…When the addition of non‐volatile diluents or ‘extenders’ is suspected, a measurement by standardization of the GC‐eluted fraction of the injected JA is mandatory 109 . It will confirm the adulteration, without the need to identify the ‘diluent’, which can, nevertheless, be performed by other techniques such as LC‐MS or NMR, 245 even at low field 246 . Still bearing in mind that GC is limited to the analysis of the volatile fraction of JA, it is helpful to characterize geographical origin of JA, when considering simply the relative percentages of selected constituents measured by internal normalization.…”

Recent Applications of Benchtop Nuclear Magnetic Resonance Spectroscopy

“…As summarized in Table 1, benchtop NMR spectroscopy has been actively used for the authentication of oils/fats and the detection of their adulteration [18,19], with main objectives including confirming the authenticity of expensive oils and the detection of their adulteration through mixing with cheap oils [14,15,20,21]. Edible oils and fats almost entirely consist of triglycerides, which are the products of glycerol esterification with fatty acids and therefore contain up to three different fatty acid residues (in terms of the number of carbons and double bonds).…”