Medicinal Plants Classification Biosynthesis and ... - Index of

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Jia Guan and Shao-Ping Li
hydroxide or barium carbonate is necessary to obtain the constituent monosaccharides. Then
the hydrolysate could be directly analyzed using TLC or PC with the help of standard
monosaccharides analyzed at the same conditions. But they have low sensitivity and accuracy
[32,84,88,96,97,144-146].
Gas chromatography (GC) is a unique and versatile technique, which is conventional
method for analysis of volatile compounds. If the sample to be analyzed is nonvolatile, the
techniques of derivatization or pyrolysis GC should be utilized. Up to date, GC has been
widely applied to determine free monosaccharides, and constituent monosaccharides of both
oligosaccharides and polysaccharides, which has the advantages of simple instrumentation,
high selectivity and high accuracy. The derivatives could be prepared using monosaccharides
with hexamethyldisilane (HMDS), trimethylchlorosilane (TMCS), trimethylsilyl (TMS),
N,O-bis-(trimethylsilyl)trifluoroacetamide (BSTFA), etc. in nonaqueous organic solvents
such as pyridine or dimethyl sulfoxide to obtain trimethylsilyl ether derivatives [147-150], or
with hydroxylamine hydrochloride and acetic anhydride to form acetate derivatives in
pyridine, butylenes oxide or methyl imidazole solvents [151-155]. FID is the commonly used
detection for GC analysis, which has better selectivity and higher sensitivity. But MS could
offer more reliable structure information for identification. The selectivity and accuracy are
also greatly improved with the help of extracted ion count [156-164].
HPLC is also extensively applied for determination of constituent monosaccharides. In
most cases, HPLC with ultraviolet (UV) detection is the prevailing technique, which has been
widely used for determination of components in Chinese medicine. However,
monosaccharides have no UV absorptivity. To detect intact monosaccharides, RI detection
has been used for analysis by HPLC [165,167]. Unfortunately, RI detector is one of the least
sensitive LC detectors, and it can not be used for gradient elution. Fluorescence derivatives of
monosaccharides could be prepared to improve the sensitivity of analysis [67]. But derivation
increases the complexity of sample preparation. The evaporative light scattering detector
(ELSD) response does not depend on the samples‘ optical characteristics, which eliminates
the problems associated with RI detector. Therefore, ELSD is increasingly being used in
liquid chromatography as a quasi-universal detector, which has been successfully applied to
analyze the compounds less volatile than the mobile phase, such as carbohydrates [166-168].
It is valuable to develop HPLC-ELSD method for direct analysis of carbohydrates, including
monosaccharides, oligosaccharides and polysaccharides. Furthermore, polysaccharide
analysis using carbohydrate gel electrophoresis (PACE) is a fast and simple technique for
sugar composition analysis relies on derivatization of reducing ends of sugars with
fluorophore [169,170], and as little as 500 fmol monosaccharides could be detected that
showed the method is more sensitive [171]. In additional, CE has been developed as an
attractive analytical method owing to its high separation efficiency, low sample consumption,
short analysis time and relatively simple instrumentation. While electrochemical detection
(ED) possesses higher sensitivity and lower detection limit than UV absorption. Hence, the
CE-ED method is successfully used in the analysis of monosaccharides [172,173]. Table 3
listed the applications of major chromatographic methods for analysis of monosaccharides in
some medicinal plants and fungi.