Novel coupled methods in high performance liquid chromatography with 1D/2D NMR detection based on low field NMR spectrometer

• Applicant: Professor Dr. Manfred Wilhelm
• Subject Area: Analytical Chemistry ; Polymer Materials ; Preparatory and Physical Chemistry of Polymers
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 540563241

The aim of the project is the development of coupled analytical methods based on high performance liquid chromatography (HPLC) hyphenated with chemically selective NMR detection. Compact low-field spectrometers based on permanent magnets are used as chemically selective detection and optimized for online coupling with HPLC. The goal is to separate analyte mixtures, characterize them simultaneously by spectroscopy, and thus enable detailed characterization that was previously unattainable. The project is pursuing several approaches to optimize the methodology, the most important aspects being solvent suppression, adaptation of 2D NMR methods for hyphenating with chromatography, and increasing the sensitivity of the methodology using a novel chromatographic method, Fourier liquid chromatography (FT-LC). The suppression of solvent signals, especially with the planned use of protonated solvents, is one of the most essential approaches for a universally applicable characterization method. The intense signals of protonated solvents, which are often a factor of 1000 above the peaks of the analytes, will be eliminated by a novel combination of different solvent suppression methods, thus optimizing sensitivity and selectivity. An important aspect of solvent suppression is the optimization for solvent gradients, which are used in HPLC for sample separation and make suppression difficult due to various effects, e.g., the drift of the chemical shift of the NMR signals. The second important approach of the project is the use of 2D NMR detection in coupling with HPLC. By adding an additional spectral dimension, much more detailed molecular information about the analytes is accessible, an example being molecular size determination via 2D DOSY experiments. One goal is to minimize the measurement time of the much more sophisticated 2D NMR experiments, since the required measurement time of spectroscopic analysis limits the resolution of chromatographic separation in the hyphenated analysis. Also of high importance for the required measurement time is the sensitivity of the methodology. Here the third aspect of the planned project comes in: The sensitivity of the methodology is to be significantly improved by the application of a new chromatographic method, also called Fourier Transformation Liquid Chromatography (FT-LC). The FT-LC was developed in size exclusion chromatography (SEC) and will in this project be established in liquid adsorption chromatography (LAC), for the analysis of small molecules. The aim of whole the project is to develop a hypenated characterization methodology that enables complete analysis of even complex mixtures of molecules and yet requires only resonable effort both in terms of acquisition and application, making it interesting for smaller laboratories as well. This opens up numerous fields of application, e.g. polymer, food and drug analysis.

• DFG Programme: Research Grants