Online Coupling of Size‐Exclusion Chromatography and Low‐Field 1H NMR Spectroscopy

Current results and limitations of a novel SEC–MR–NMR (size‐exclusion chromatography–medium resolution nuclear magnetic resonance) system are presented, delivering a direct correlation of chemical structure and molecular weight. A 20 MHz 1H NMR spectrometer based on permanent magnets was combined with a SEC setup. The NMR sensitivity was improved by digital filters, shims, and a self‐built flow probe when compared with time‐domain instruments. For optimum NMR signal‐to‐noise ratio (S/N) of polymer fractions and concomitantly reduced S/N of solvent signals, deuterated solvents or protonated solvents, with solvent suppression, were applied. Results are presented after optimization of both NMR and chromatographic components such as column dimension and volume flow.