Extraction Technologies for Medicinal and Aromatic ... - Capacity4Dev

EXTRACTION TECHNOLOGIES FOR MEDICINAL AND AROMATIC PLANTS
this component from the others nearest to it by a ΔR f value of at least 0.15.
In contrast to TLC, fl ash chromatography separations are governed by column
volumes.
A column volume (CV) is defi ned as the volume of solvent required
to fi ll all the adsorbent pores and interstitial spaces between adsorbent
particles in a given column. The volume required to elute a compound
of interest from a column is expressed in terms of the number of CV. The
volume that separates the elution of two substances from the same volume
is called column volume difference (ΔCV). The ideal fl ash chromatography
solvent system is one that elutes the desired compound of interest in 3-6
CV and that separates this component from others nearest to it by a ΔCV
greater than 1.
The relationship between numbers of CV to R f for a given compound
is 1/ R f ; therefore, for two compounds ΔCV = 1/ R f1 - 1/ R f2. For a
particular set of separation conditions, a weakly retained, fast-eluting component
with an R f =0.9 can be eluted in just over 1 CV, whereas a strongly retained,
slow-eluting component with an R f =0.1 requires 10 CV for complete
elution (Table 1).
Table 1: Relationship between R f and CV
R f
CV
0.90 1.10
0.70 1.40
0.50 2.00
0.30 3.33
0.10 10.0
Due to factors such as change in the TLC solvent fl ow rate with
respect to time and interference from adhesives used to bind TLC sorbents,
solvent conditions that provide an acceptable TLC separation will not necessarily
work effectively for fl ash chromatography without modifi cation.
Although some empirical experimentation may be required, the
steps below help streamline the process of converting a TLC solvent system
into a fl ash chromatography mobile phase:
1. Use matching sorbent chemistries on the TLC plate and in the
fl ash chromatography column. Stationary phase sorbent chemistries
(including silica) can differ from one manufacturer to another. It is
important to match these sorbent chemistries if the solvent systems
are expected to provide equivalent results.
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