Analytical Evaluation of Low-Field ³¹P NMR Spectroscopy for Lipid Analysis

Abstract

We investigate the potential of 31 P NMR with simple, maintenance-free benchtop spectrometers to probe phospholipids in complex mixtures. 31 P NMR-based lipidomics has become an important topic in a wide range of applications in food-and health-sciences, and the continuous improvements of compact, maintenance-and cryogen-free instruments opens new opportunities for NMR routine analyses. A prior milestone is the evaluation of the analytical performance provided by 31 P NMR at low magnetic field. To address this, we assess the ability of state-ofthe-art benchtop NMR spectrometers to detect, identify, and quantify several types of phospholipids in mixtures. Relying on heteronuclear crosspolarization experiments, phospholipids can be detected in 2 h with a limit of detection of 0.5 mM at 1 T and 0.2 mM at 2 T, while the headgroups of phosphatidylcholine (PC), phosphatidyl-ethanolamine (PE), phosphatidylinositol (PI), phosphatidylserine (PS), and phosphatidyl-glycerol (PG) can be unambiguously assigned based on 2D 1 H− 31 P total correlated spectroscopy (TOCSY) spectra. Furthermore, two quantitative methods to obtain absolute concentrations are proposed and discussed, and the performance is evaluated regarding precision and accuracy.

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

“…The non‐research real‐life application of LF‐NMR as a first screening tool of seized drugs with a large library and automated data treatment is the way to go 41 . Food and health applications are varied too, ranging from fraud detection, metabolite screening of food ingredients, 45 lipidomics by means of 1 H‐ and 31 P‐NMR, 46 and point‐of‐care metabolomics 49 . Potentially healthcare applications are a huge market for LF‐NMR.…”

“…Gouilleux et al . used 2D 1 H/ 31 P NMR to probe phospholipids at the mM level at 43.5 and 80.5 MHz (for 1 H) 46 . By means of a total correlated spectroscopy (TOCSY) experiment (60 mg α‐lecithin, 12 h), they were able to separate phosphadityl‐ethanolamine, phosphaditylinositol and phosphaditylcholine and determine their relative concentrations.…”

“…Absolute quantitation proved possible by two different methods (relaxation reagent or 1 H excitation and magnetisation transfer to 31 P) both overcoming long 31 P relaxation times. Both methods had their pros and cons but both yielded fair accuracy (maximum 0.5–9% deviation) and relative standard deviations (RSDs) (2–5%) making LF‐NMR a promising tool for lipidomics 46 …”

A Pipeline for Making 31P NMR Accessible for Small- and Large-Scale Lipidomics Studies

“…The desire to acquire lipidomics data using 31 P NMR has led to the development of solution phase solvent systems for the purpose. Several solvent systems have been tested, including detergent-based systems [27][28][29] and chloroformmethanol mixtures [30][31][32][33]. However, high viscosity and difficulty in recovering the sample (detergent systems), and relatively low solubility of lipids (chlorinated solvents) have limited the use of these particular solvent systems in detailed lipidomics studies involving batches of samples.…”

A pipeline for making 31P NMR accessible for small- and large-scale lipidomics studies

“…The desire to acquire lipidomics data using 31 P NMR has led to the development of solution phase solvent systems for the purpose. Several solvent systems have been tested, including detergent-based systems [31][32][33] and chloroform-methanol mixtures [34][35][36][37]. However, high viscosity and difficulty in recovering the sample (detergent systems), and relatively low solubility of lipids (chlorinated solvents) have limited the use of these particular solvent systems in detailed lipidomics studies involving batches of samples.…”