Size-exclusion chromatography of cellulose: observations on the low-molar-mass fraction
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ORIGINAL RESEARCH
Size-exclusion chromatography of cellulose: observations on the low-molar-mass fraction Leena Pitka¨nen
. Herbert Sixta
Received: 27 April 2020 / Accepted: 22 August 2020 Ó The Author(s) 2020
Abstract Accurate determination of molar mass distribution for disperse cellulose samples has proved to be a challenging task. While size-exclusion chromatography coupled to multi-angle light scattering (MALS) and differential refractive index (DRI) detectors has become the most commonly used method for molar mass determination of celluloses, this technique suffers low sensitivity at the low-molar mass range. As discussed here, the universal method for accurate molar mass distribution analysis of cellulose samples not exists and thus thorough understanding on the differences of the various methodological approaches is important. In this study, the focus is in the accurate determination of the lowmolar mass fraction. The results obtained by combining the two calibration strategies, MALS/DRI for polymeric region of a cellulose sample and conventional calibration for oligomeric region, was compared to the results obtained using only MALS/DRI (with extrapolation of the curve where signal-to-noise of MALS is low). For birch pulp sample, the results from the two approaches were comparable; it should be highlighted, however, that MALS/DRI slightly overestimates the molar masses at the low-molar-mass region.
L. Pitka¨nen (&) H. Sixta Department of Bioproducts and Biosystems, Aalto University, P.O. Box 16300, 00076 Espoo, Finland e-mail: [email protected]
Keywords Size-exclusion chromatography Cellulose Cello-oligomers Oligomeric region Light-scattering detection
Introduction Accurate knowledge on the molar mass distribution of polymeric material is often important when evaluating the material’s structure–function properties. This applies also for highly disperse biopolymers, such as polysaccharides. Molar mass determination of polysaccharides is not a straightforward task (Maina et al. 2014; Potthast et al. 2015; Striegel et al. 2009a). Variation in chain length, heterogeneous chemical composition, challenges in dissolution, and impurities complicates the molar mass determination of polysaccharides, among other factors. A good example is cellulose, the most abundant renewable material, which commonly has a broad chain length distribution from oligomeric material to ultra-high molar mass chains, and a very limited solubility in common solvents. A lot of effort has been made in order to find ‘‘a universal method’’ for accurate molar mass determination of cellulose (Potthast et al. 2015) but the complexity of the material makes this task mission impossible. Critical evaluation of the pros and cons of different methods deserves, however, to be thoroughly discussed.
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Cellulose
In order to obtain information on the distribution of different chain lengths, separation technique is needed to separate the fractions with different sizes. Sizeexclusion
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