Coupling SEC with medium-resolution NMR

The capabilities of a new SEC-medium-resolution NMR system for polymer analysis have been demonstrated in various modes of operation with proton and deuterated solvents. Size exclusion chromatography has been lnked with NMR before, but only with high-field instruments which are expensive to acquire, so the combined technique has not become widespread. Now, scientists from the Karlsruhe Institute of Technology and PSS Polymer Standards Service GmbH, Mainz, Germany, have successfully linked SEC with a low-field NMR spectrometer operating at about 20.1 MHz, as described in Macromolecular Chemistry and Physics.

The sensitivity of the NMR system was improved by various instrumental manipulations and by the use of a custom-built flow probe for sample introduction. The conditions were adjusted to gain the best compromise between the quality of the chromatograms and the signal-to-noise ratio in the acquired spectra, using polymer solutions for the tests. The system was demonstrated in online and stopped-flow modes with proton and deuterated solvents, the latter introducing a solvent suppression factor of 300 to allow the polymer signals to be detected directly.