Characterization of Carboxymethyl Cellulose by MALDI-TOFMS

Abstract: Carboxymethyl cellulose (CMC) is a cellulose derivative, made from cellulose by introduction of carboxymethyl groups along the molecules. The properties of CMC are affected by several parameters where the molar mass and molar mass distribution, degree of substitution (DS) and the distribution pattern along the cellulose backbone are the most prominent.In the present thesis we have investigated the use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) for characterization of the chemical structure of CMC. We here present a refined sample preparation procedure where ammonium sulphate is added to the sample/matrix mixture and thereby greatly facilitates the spectrum acquisitions and improves the quality of the mass spectrum. When applying the refined method on commercial CMCs, from partial acidic hydrolysis, it was shown that MALDI-TOFMS can be used for estimation of the DS in the intact samples as a compliment to more expensive and laborious methods. We also show that by combining MALDI-TOFMS with selective hydrolysis, by purified endoglucanase, and size-exclusion chromatography (SEC) it is possible to differentiate between CMCs of similar monomer composition but differences in the substitution pattern. Our findings show that the CMC containing longer non-substituted cellulose segments along the polymer backbone also displayed the highest intermolecular interactions in solution, as measured by rheometry.