process involves solvent, a pump, an injector, a column, a detector, and a recorder
(Fig. 10.9) (Barnes 1992; Engelhardt 2012).
Once a column has been selected according to the characteristics of the substance to be analyzed (molecular weight, ionic character, solubility, etc.), a suitable
mobile phase is used to separate the specimen. Once separation has been performed,
a detector is selected with strong sensitivity and selectivity for the specimen, as well
as a suitable band range and low detection threshold. Detectors come in many
different kinds; in the case of UV/VIS detectors, specific wavelengths of light from
a light source are projected through a device onto a sample within a cell known as a
specimen vessel. Part of it is absorbed, while part of it passes through the specimen.
For certain specimens, absorbance for light from particular wavelengths is high, and
the intensity of light passing through the specimen decreases. In this case, the
amount of light absorbed is related to factors such as the concentration of absorbent
samples within the solution, the light wavelength, and the distance over which the
light passes through the sample. This means that if a substance can be dissolved
with a suitable solvent, it can be separated and analyzed with liquid chromatography, regarded of its volatility, stability with respect to light, organic and inorganic
compounds, and molecular weight (Gerber et al. 2004).
10.2.7 Analyzing Marine Natural Products Structure
For the chemical structure of a natural substance to be determined, the substance
used in the experiment must first be refined to at least 95% purity. Analysis cannot
provide perfect information about structure when the specimen has not been
thoroughly refined, which renders any structural analysis of the desired substance
impossible. Analysis must therefore be performed after the specimen has been
refined to maximum purity.
The following methods may typically be used for structural analysis of refined
natural substances. The first group includes methods in which light and other
electromagnetic waves are separated by wavelength for analysis based on molecular
absorption or emission (including UV/VIS absorption, infrared absorption, and
nuclear magnetic resonance), and while the second group consists of other methods
(element analysis, mass analysis, X-ray diffraction analysis, etc.).
Comparison of the UV/VIS absorption spectrum with a substance’s anticipated
spectrum can be used to identify functional or reactive groups in a compound and
gauge the presence of impurities. The IR absorption spectrum can be used to
estimate the presence of functional groups in a compound and side chains such as
unsaturated bonds. Nuclear magnetic resonance (NMR) can be used to determine
the relative quantities of hydrogen and carbon and bonding state. Mass analysis can
be used not only for molecular weight and structural units such as functional
groups, but also for molecular formulas.
These methods of analysis may be used to estimate the structure of unknown
specimens.
362
10 Marine Natural Substances
(Fig. 10.9) (Barnes 1992; Engelhardt 2012).
Once a column has been selected according to the characteristics of the substance to be analyzed (molecular weight, ionic character, solubility, etc.), a suitable
mobile phase is used to separate the specimen. Once separation has been performed,
a detector is selected with strong sensitivity and selectivity for the specimen, as well
as a suitable band range and low detection threshold. Detectors come in many
different kinds; in the case of UV/VIS detectors, specific wavelengths of light from
a light source are projected through a device onto a sample within a cell known as a
specimen vessel. Part of it is absorbed, while part of it passes through the specimen.
For certain specimens, absorbance for light from particular wavelengths is high, and
the intensity of light passing through the specimen decreases. In this case, the
amount of light absorbed is related to factors such as the concentration of absorbent
samples within the solution, the light wavelength, and the distance over which the
light passes through the sample. This means that if a substance can be dissolved
with a suitable solvent, it can be separated and analyzed with liquid chromatography, regarded of its volatility, stability with respect to light, organic and inorganic
compounds, and molecular weight (Gerber et al. 2004).
10.2.7 Analyzing Marine Natural Products Structure
For the chemical structure of a natural substance to be determined, the substance
used in the experiment must first be refined to at least 95% purity. Analysis cannot
provide perfect information about structure when the specimen has not been
thoroughly refined, which renders any structural analysis of the desired substance
impossible. Analysis must therefore be performed after the specimen has been
refined to maximum purity.
The following methods may typically be used for structural analysis of refined
natural substances. The first group includes methods in which light and other
electromagnetic waves are separated by wavelength for analysis based on molecular
absorption or emission (including UV/VIS absorption, infrared absorption, and
nuclear magnetic resonance), and while the second group consists of other methods
(element analysis, mass analysis, X-ray diffraction analysis, etc.).
Comparison of the UV/VIS absorption spectrum with a substance’s anticipated
spectrum can be used to identify functional or reactive groups in a compound and
gauge the presence of impurities. The IR absorption spectrum can be used to
estimate the presence of functional groups in a compound and side chains such as
unsaturated bonds. Nuclear magnetic resonance (NMR) can be used to determine
the relative quantities of hydrogen and carbon and bonding state. Mass analysis can
be used not only for molecular weight and structural units such as functional
groups, but also for molecular formulas.
These methods of analysis may be used to estimate the structure of unknown
specimens.
362
10 Marine Natural Substances