Extraction Technologies For Medicinal And Aromatic Plants - Unido

EXTRACTION TECHNOLOGIES FOR MEDICINAL AND AROMATIC PLANTS
12 Flash Chromatography and Low
Pressure Chromatographic Techniques
for Separation of Phytomolecules
Abstract
S. K. Chattopadhyay
Flash chromatography is a rapid form of preparative column chromatography that
employs prepacked columns through which a solvent is pumped at high fl ow rate. Two
types of solvent systems are used in fl ash chromatography: isocratic and gradient. In
the isocratic system, a single-strength mobile phase brings about the desired separation.
The gradient system, in which the solvent composition changes during the course
of elution, is suited for complex samples containing compounds that differ greatly in
column retention times. The optimum fl ow rate for a fl ash separation is related to the
particle size and dimensions of the column. Typical sorbents for normal phase fl ash
chromatography are polar (e.g. silica, NH2) and elution solvents are non-polar. In reverse
phase chromatography, the stationary phase is non-polar (such as C18) and the
mobile phase is polar. Compounds are retained by the interaction of their non-polar
functional groups with the non-polar groups on the packing surface. Therefore, the
most polar compounds elute fi rst followed by other compounds in decreasing order
of polarity. To achieve a desired separation, one must select a sorbent that effectively
retains the compounds of interest under solvent conditions that are appropriate for the
sample’s solubility. Sample loading onto a fl ash column can be done with wet loading
(the liquid sample is loaded directly and allowed to percolate into the sorbent bed) or
dry loading (when samples are pre-absorbed to a small amount of sorbent which is
then loaded onto the column).
12.1 Introduction
Mikhail Semyonovich Tsvet of Russia invented the fi rst chromatographic
technique in 1901 during his research on chlorophyll. He used
a liquid adsorption column containing calcium carbonate to separate plant
pigments. The method was described on 30 December 1901 at the XIth
Congress of Naturalists and Doctors in St. Petersburg. The fi rst printed description
was published in 1903 in the Proceedings of the Warsaw Society of
Naturalists, section of biology. He fi rst used the term chromatography in print
in 1906 in his two papers about chlorophyll in the German botanical journal,
Berichte der Deutschen Botanischen Gesellschaft.
In 1952, Archer John Portor Martin and Richard Laurence Millington
Synge were awarded the Nobel Prize in Chemistry for their invention
of partition chromatography. Since then, the technique has advanced rapidly.
Researchers have found that the principles underlying Tsvet’s chromatography
can be applied in many ways, giving rise to the different varieties of
chromatography and allowing increasing similar molecules to be resolved.
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