Application of size exclusion electrochromatography to the microanalytical determination of the molecular mass distribution of celluloses from objects of cultural and historical value

摘要

The molecular mass distributions (MMD) of celluloses from paper and other sources were determined by size exclusion electrochromatography (SEEC). Prior to the separation the celluloses were chemically modified with phenyl isocyanate into their tricarbanilate derivatives (CTC). Sensitive UV detection of the CTC could be performed at a wavelength of 210 nm. The solvent used for separation was acetone. With this solvent, a high electroosmotic flow could be generated in columns packed with bare silica particles. With a column packed with particles with a nominal pore size of 30 nm, use of a mobile phase with a salt concentration of 0.1 mM was found to be optimal with respect to mass selectivity and efficiency. The workable mass range under these conditions was from 2 kDa to at least 500 kDa for (native) celluloses. The SEEC method was compared to classical pressure-driven size exclusion chromatography (PD-SEC). It is shown that the two methods give comparable results for the MMD of celluloses, while SEEC has important advantages in terms of speed and sample consumption. With SEEC, the analysis time was less than 20 min. The method was applied for the study of cellulose degradation during (artificial) aging of paper samples. A clear reduction of the average molecular mass of cellulose during aging was observed. With SEEC, the required sample amount is strongly reduced compared to classical PD-SEC. With a single paper fiber (after derivatization), multiple analyses could be carried out. It is argued that this is not only important for the analysis of unique objects but that it also allows the detection of MMD heterogeneities on a microscale. The strong reduction in sample size may be relevant when local heterogeneities in other types of polymer samples are studied. [References: 25]