Characterisation of mass distributions of solvent-fractionated lignins using analytical ultracentrifugation and size exclusion chromatography methods.

Lignins are valuable renewable resources for the potential production of a large array of biofuels, aromatic chemicals and biopolymers. Yet native and industrial lignins are complex, highly branched and heterogenous macromolecules, properties that have to date often undermined their use as starting materials in lignin valorisation strategies. Reliable knowledge of weight average molar mass, conformation and polydispersity of lignin starting materials can be proven to be crucial to and improve the prospects for the success of such strategies. Here we evaluated the use of commonly-used size exclusion chromatography (SEC)-calibrated with polystyrene sulphonate standards-and under-used analytical ultracentrifugation-which does not require calibration-to characterise a series of lignin fractions sequentially extracted from soda and Kraft alkaline lignins using ethyl acetate, methyl ethyl ketone (MEK), methanol and acetone:water (fractions F01-F04, respectively). Absolute values of weight average molar mass (Mw) determined using sedimentation equilibrium in the analytical ultracentrifuge of (3.0 ± 0.1) kDa and (4.2 ± 0.2) kDa for soda and Kraft lignins respectively, agreed closely with previous SEC-determined Mws and reasonably with the size exclusion chromatography measurements employed here, confirming the appropriateness of the standards (with the possible exceptions of fraction F05 for soda P1000 and F03 for Indulin). Both methods revealed the presence of low (~ 1 kDa) Mw material in F01 and F02 fractions followed by progressively higher Mw in subsequent fractions. Compositional analysis confirmed > 90% (by weight) total lignins successively extracted from both lignins using MEK, methanol and acetone:water (F02 to F04). Considerable heterogeneity of both unfractionated and fractionated lignins was revealed through determinations of both sedimentation coefficient distributions and polydispersity indices. The study also demonstrates the advantages of using analytical ultracentrifugation, both alongside SEC as well as in its own right, for determining absolute Mw, heterogeneity and conformation information for characterising industrial lignins.

Electrospray ionization quadrupole time-of-flight tandem mass spectrometric analysis of hexamethylenediamine-modified maltodextrin and dextran.

A combined methodology for obtaining at the preparative scale and characterization by nanoelectrospray ionization (nanoESI) quadrupole time-of-flight (QTOF) mass spectrometry (MS) and tandem MS (MS/MS) of linear polysaccharides modified at the reducing end is presented. Two polydisperse maltodextrins (1000 and 3000 Da) and a high molecular weight polydisperse dextran (6000 Da) were coupled with hexamethylenediamine (HMD). The coupling products were analyzed by nanoESI-QTOF-MS in the positive ion mode and MS/MS using collision-induced dissociation (CID) at low energies. In the HMD-M1000 mixture, the polysaccharide chains containing from 2 to 8 Glc residues were detected, while in HMD-M3000 we identified a complete series of chains containing from 8 to 21 Glc moieties. The employed ESI conditions enhanced the detection of chains with up to 46 Glc residues in the HMD-D6000 sample. By optimized MS/MS, HMD-modified polysaccharides of 3, 4, 5, 12 and 46 degrees of polymerization yielded product ion spectra exhibiting the whole set of Y- and B-fragment ions. The MS structural data were obtained within a few minutes of signal acquisition, with a sample consumption situating the analysis sensitivity in the picomolar range.