Filling the gap: Calibration of the low molar-mass range of cellulose in size exclusion chromatography with cello-oligomers

Abstract

Degraded celluloses are becoming increasingly important as part of product streams coming from various biorefinery scenarios. Analysis of the molar mass distribution of such fractions is a challenge, since neither established methods for mono- or disaccharides nor common methods for polysaccharide characterization cover the intermediate oligomer range appropriately. Size exclusion chromatography (SEC) with multi-angle laser light scattering (MALLS), the standard approach for celluloses, suffers from decreased scattering intensities in the lower-molar mass range. The limitation in the low-molecular range can, in principle, be overcome by calibration, but calibration standards for such “short” celluloses are either not readily available or structurally remote and thus questionable. In this paper, we present the calibration of a SEC system— for the first time – with monodisperse cellooligomer standards up to about 3400gmol−1. These cellooligomers are “short-chain celluloses” and can be seen as the “true” standard compounds, by contrast to commonly used standards that are chemically different from cellulose, such as pullulan, dextran, polystyrene, or poly(methyl methacrylate). The calibration is compared against those commercial standards and correction factors are calculated. Calibrations with non-cellulose standards can now be adjusted to yield better fitting results, and data already available can be corrected retrospectively.