Handbook of Size Exclusion Chromatography and Related ...

isolated lignins because they are enriched in carbonyl and carboxyl groups.
The fast pyrolysis of solid biomass into a liquid produces an insoluble residue
(pyrolytic lignin) (50). The MMD and structure of the pyrolytic lignin has been
determined and by combining results an average DP of 4 to 9 was obtained.
The use of HPSEC systems with alkaline eluents is restricted due to
instability or interactions with the packing material. Recently several
investigations have used Ultrahydrogel columns with eluents in the pH range of
6.5–12.0 and with salt solutions of 0.05 M LiCl, 0.1 M NaNO3 as eluents (51,52).
The ionic strength and pH value of the mobile phases have significant influences
on the flow behaviors of the molar mass standards and lignins. It was shown that
neutral aqueous eluents containing low concentration of electrolytes could
separate degradation products of lignosulfonates. The best results were obtained
by using 0.05 M LiCl at pH 6.5 as eluent. The above system was employed to
measure relative MMD of lignin dispersants (53). Because of an increase in
hydrophilicity, sulfonated lignins may be investigated in aqueous eluents.
The number- and weight-average MMs and MMDs of alkali lignins from
eucalyptus and kraft lignin of birch have also been determined by aqueous HPSEC
(54) taking into consideration the ionic strength and pH value of the eluent. The
relative MM and MMD of lignosulfonates and sulfonated soda lignin samples (55)
were determined by aqueous SEC. When 0.1 M NaNO3 was used as mobile phase
(eluent) an improved chromatographic resolution and decreased nonsize exclusion
effect could be obtained. The MMs of alkali lignins were also determined by
Ultrahydrogel columns calibrated with pullulans (56). Several mobile phases were
tested and the ion strength and pH value of mobile phase affected greatly the
adsorption of alkali lignin. It was shown, as expected, that the increase in ionic
strength and pH caused a decrease in adsorption. When the pH was 12 adsorption
disappeared. A review about SEC in determining the relative MM of lignin (57)
has been presented. The molar masses of alkali lignins have also been determined
using aqueous SEC, Ultrahydrogel column, and 0.01 M NaOH (pH 12) as eluent
(58). The results were comparable to those obtained by a THF–SEC system. The
MMD of kraft lignin from eucalyptus wood pulping was also investigated using
aqueous eluents and Ultrahydrogel columns (59).
The structures and MMD of alkali lignins obtained by extraction with 5, 7.5,
and 10% NaOH from fast growing poplar have also been investigated (60). A
similar work was performed on soda-anthraquinone lignin, from oil palm empty
fruit bunch (EFB), but the fractionation was obtained by successive extractions
with dichloromethane, n-PrOH, and MeOH–dichloromethane (61). The relative
molar masses of the fractions increased from 2630 to 4380.
A sulfomethylolated ALCELL lignin sample has been used as a waterreducing
additive in cement paste. The importance of MM on the performance of
the lignins was investigated by dividing it (62) into four fractions of different MM
by means of membrane ultrafiltration. The MMD and average MM (M n, M w, M z,
© 2004 by Marcel Dekker, Inc.