Some of the methods used for separation and refinement of natural marine
substances include precipitation (using differences in solvency), fractional distillation (using differences in boiling point), sublimation (using sublimation capabilities), partitioning (using differences in partition coefficient), and
chromatography. Chromatography is the most widely used of these (Heathcock
1996; Nicolaou et al. 2000).
Depending on the principle used for separation, chromatography can be separated into adsorption column chromatography, which uses differences in adsorption
and desorption between a substance’s stationary and mobile phase, and partition
column chromatography, which uses partitioning. Various types exist, including ion
exchange column chromatography (which uses an ion exchanger), thin layer
chromatography (TLC), gel column chromatography, and high performance liquid
chromatography (HPLC).
In adsorption column chromatography, emission begins where polarity is
smallest; this is referred to as normal phase chromatography (NP). The inverse of
this is partition column chromatography, in which emission begins where polarity is
largest; this is known as reverse phase chromatography (RP) (IUPAC 1997).
One example of the use of column chromatography for separation and refinement of natural substances takes place in open column chromatography using silica
gel. Fractions obtained with solvent are separated by solvent fraction and subjected
to TLC examination and testing, after which HPLC are used for separation and
refinement.
A. Adsorption Column Chromatography
Adsorption is a phenomenon is which a substance dissolved in gaseous or liquid
solvent bonds physically or chemically with a solid. Solids in which adsorption
occurs are known as adsorbents, while the adsorbing solute is known as adsorbate.
Adsorption occurs because of interactions between molecules on the adsorbent
surface and molecules in the solution. It may be classified into physical adsorption,
which occurs because of physical interactions, and chemical adsorption, which
results from chemical forces. Typically, physical adsorption is characterized by the
relatively fast and reversible formation of adsorbents, while chemical absorption is
more powerful than physical absorption and may be reversible, depending on the
case.
In many cases, separation and refinement of natural substances employs physical
adsorption, which is simpler than the more powerful chemical adsorption, where
separation through solvent is difficult. Because adsorption and desorption in the
column involves mutual action by the adsorption strength of the substance and
adsorbent and the properties of the solvent separating the substance absorbed by the
adsorbent, thorough knowledge of their characteristics is essential.
Typical examples of adsorbents used for separating natural substances include
silica gel, active carbon, and alumina. Silica gel is the most widely used adsorbent
for separation of natural substances, especially in cases of low-polarity soluble
substances and non-ionic organic compounds.
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10 Marine Natural Substances
substances include precipitation (using differences in solvency), fractional distillation (using differences in boiling point), sublimation (using sublimation capabilities), partitioning (using differences in partition coefficient), and
chromatography. Chromatography is the most widely used of these (Heathcock
1996; Nicolaou et al. 2000).
Depending on the principle used for separation, chromatography can be separated into adsorption column chromatography, which uses differences in adsorption
and desorption between a substance’s stationary and mobile phase, and partition
column chromatography, which uses partitioning. Various types exist, including ion
exchange column chromatography (which uses an ion exchanger), thin layer
chromatography (TLC), gel column chromatography, and high performance liquid
chromatography (HPLC).
In adsorption column chromatography, emission begins where polarity is
smallest; this is referred to as normal phase chromatography (NP). The inverse of
this is partition column chromatography, in which emission begins where polarity is
largest; this is known as reverse phase chromatography (RP) (IUPAC 1997).
One example of the use of column chromatography for separation and refinement of natural substances takes place in open column chromatography using silica
gel. Fractions obtained with solvent are separated by solvent fraction and subjected
to TLC examination and testing, after which HPLC are used for separation and
refinement.
A. Adsorption Column Chromatography
Adsorption is a phenomenon is which a substance dissolved in gaseous or liquid
solvent bonds physically or chemically with a solid. Solids in which adsorption
occurs are known as adsorbents, while the adsorbing solute is known as adsorbate.
Adsorption occurs because of interactions between molecules on the adsorbent
surface and molecules in the solution. It may be classified into physical adsorption,
which occurs because of physical interactions, and chemical adsorption, which
results from chemical forces. Typically, physical adsorption is characterized by the
relatively fast and reversible formation of adsorbents, while chemical absorption is
more powerful than physical absorption and may be reversible, depending on the
case.
In many cases, separation and refinement of natural substances employs physical
adsorption, which is simpler than the more powerful chemical adsorption, where
separation through solvent is difficult. Because adsorption and desorption in the
column involves mutual action by the adsorption strength of the substance and
adsorbent and the properties of the solvent separating the substance absorbed by the
adsorbent, thorough knowledge of their characteristics is essential.
Typical examples of adsorbents used for separating natural substances include
silica gel, active carbon, and alumina. Silica gel is the most widely used adsorbent
for separation of natural substances, especially in cases of low-polarity soluble
substances and non-ionic organic compounds.
356
10 Marine Natural Substances