Handbook of Size Exclusion Chromatography and Related ...

dextrans swell too much in cadoxen solutions, cellulose–cadoxen solutions have
been characterized using 0.5 MNaOH as mobile phase.
5.2 Lithium Chloride/N,N-Dimethylacetamide
Among the investigated solvents for dissolution of cellulose, lithium chloride/
N,N-dimethylacetamide (LiCl/DMAc) has provento be the most successful to be
used in SEC. The first report on LiCl/DMAc as solvent for cellulose appeared in
1981 (38,62). Anumber of models for the solvent–cellulose complex have been
proposed and reviewed recently (66,68). The first report about the application of
LiCl/DMAcforSECofcelluloseappearedin1986(185).Sincethen,anumberof
underivatized cellulosic samples have been characterized by SEC. Examples are
cotton fibers (186–190), different kinds of cellulose samples from cotton (190–
201), ramie (202), wood pulps from the sulfite process (191,201,203–207), and
wood pulps from the kraft process (191,196,199,200,204,208–214). The
stationaryphaseusediscrosslinkedPS/DVBparticles.Reportedchromatographic
conditions are summarized in Table 9.
Cellulose–LiCl/DMAc solutions suitable for SEC are in principle simple to
prepare. The sample, in the concentration range 0.8–1.25% (wt/vol) is dissolved
using high concentrations of LiCl, typically 8–10% (wt/vol). The concentrated
solution is then diluted about ten times. However, for successful dissolution of the
cellulosic sample, activation prior to dissolution is necessary. There are two
principal ways of activating the sample, in the following denoted procedures I and
II, respectively. In both procedures, stirring during dissolution is recommended.
Swelling of cellulose in a polar medium followed by solvent exchange is the
most common way of activation, here called procedure I. The sample is commonly
soaked in water either at ambient temperature (190,197,198) or at 48C
(200,209,212). Swelling in steam or liquid ammonia has also been reported
(62). Recently, the benefit of swelling sulfite pulp samples and cotton linter
samples in a solution of 0.1 M LiCl in deionized water has been reported (206). In
the same study, consecutive washing with chelating agents (DTPA and EDTA) and
aqueous citric acid to remove metal ions was reported to facilitate the dissolution
of the samples. Although the swelling requires a polar medium, it has to be
carefully removed before dissolution in LiCl/DMAc. The solvent change is
commonly made using acetone and/or methanol several times, and finally always
by using neat DMAc. A solution of LiCl/DMAc is added to the sample, which is
generally dissolved at 48C. The time for complete dissolution is highly dependent
on concentration, DP, crystallinity, and lignin content of the sample as well as on
the LiCl concentration. Generally dissolution is obtained within one day, but high
molecular mass samples, especially those containing hemicellulose and lignin,
may need up to five days before dissolution is achieved.
© 2004 by Marcel Dekker, Inc.