Use of Pulsed Gradient Spin−Echo NMR as a Tool in MALDI Method Development for Polymer Molecular Weight Determination

Abstract

This study shows how mass spectrometry and pulsed gradient spin-echo (PGSE) nuclear magnetic resonance can be advantageously combined to achieve more reliable molecular weight information for polymers. Specifically, PGSE was shown to be a convenient tool for a rapid evaluation of Mw values to be further used as guidelines in matrix-assisted laser desorption/ionization (MALDI) sample preparation. PGSE calibration curves, established under given experimental conditions, were shown to be particularly robust, as they could be applied satisfactorily on different commonly available NMR instruments and different time frames. PGSE results were shown to compare well with size exclusion chromatography data used as a reference to validate this alternative technique. Moreover, because PGSE is relatively fast, it can be used interactively with MALDI analysis to check and understand mass spectrum profiles. This approach was first tested on poly(methyl methacrylate) (PMMA) standards and then successfully applied to determine the molecular weight of two unknown samples, a PMMA and a poly(ethylene glycol) monomethacrylate polymer.