Medicinal Plants Classification Biosynthesis and ... - Index of

286
Techniques
CE
LLS
NMR
Jia Guan and Shao-Ping Li
Table 2. (Continued)
Methods
Solvent Column Detection
Not mentiond Whatman No. 1 filter
paper
Boric acid–KOH
buffer
H2O, NaCl and
LiCl/Me2SO
Uncoated fused-silica
capillary
Periodic acid and
fuchsin-sulphurous
acid regent
Propose Ref.
Purity 27
UV 254 nm Purity 42
- - MW 30,141
D2O - DOSY Purity,
MW
37, 67
HPLC, High performance liquid chromatography; GCC, Gel column chromatography; TLC, Thin
layer chromatography; PC, Paper chromatography; High-voltage PE, High-voltage paper
electrophoresis; CE, Capillary electrophoresis; LLS, Laser light scattering detector; NMR,
Nuclear magnetic resonance; SEC, Size-exclusion column; RI, Refractive index; UV, Ultraviolet;
ELSD, Evaporative light scattering detector; MALLS, Multiangle laser light scattering detector;
RALLS, Right angle laser light scattering; MALDI-TOF MS, Matrix-assisted laser
desorption/ionization-time of flight mass spectrometery; DOSY, Diffusion ordered spectroscopy.
3.2. Molecular Weight and the Distribution
The molecular size of polysaccharides is an important physico-chemical parameter which
correlates with its biological activity. It was reported that levan antitumour activities depend
on the polysaccharide molecular weight and that a specific class of molecular weight may be
responsible for this effect [39]. The moderate molecular mass of the polysaccharides from
Poria cocos sclerotium also contributed beneficial to enhancement of antitumor activity [68].
The similar results were also obtained in other studies [69-73]. Therefore, the determination
of the molecular mass is very important for quality control of polysaccharides.
There are several concepts for molecular mass of polysaccharides, which is different
from that of small molecule compound. They are the peak average molecular weight (Mp,
average molecular weight at peak apex), the weight average molecular weight (Mw) and the
number average molecular weight (Mn). The ratio of Mw to Mn (Mw/Mn) is an indicator of
molecular weight homogeneity for the sample, which is a measure of the width of the
molecular weight distributions, and the higher the ratio, the greater the width of the
distribution. In general, a homogenous material will have a ratio of 1.0. Several techniques
have been applied for the determination of molecular mass of polysaccharides. They are mass
spectrophotometry, osmotic pressure method, vapor pressure method, analytical
ultracentrifugation, viscosity measurements [74], light scattering [75], high performance
capillary electrophoresis (HPCE) [76], HPLC [77-79] and NMR [36], etc. One useful
technique that is capable of investigating whole molar mass distribution is SEC, which is also
known as GPC or GFC. Its basic principle is the separation of molecules according to size.