Extraction Technologies for Medicinal and Aromatic ... - Capacity4Dev

13 COUNTER-CURRENT CHROMATOGRAPHY
• The mobile phase is then eluted through the column while
the column is rotated at the optimum rate.
• In the second method, after the column is fi lled with stationary
phase, the mobile phase is eluted through the column at
a desired rate until the solvent front emerges and hydrodynamic
equilibrium is established throughout the column as
evidenced by diminished carryover of the stationary phase.
• The sample is then injected into the column through the
sample port.
Each method has advantages. The second method gives a
clear tracing of the elution curve because of the minimum carryover of the
stationary phase from the column.
The first method produces a distinct solvent front and saves separation
time by eliminating the waiting period to reach hydrodynamic equilibrium.
as in HPLC.
One can conveniently use an injection valve with a sample loop
13.5.1.10 On-line Monitoring of Effluent
• The effl uent from the outlet of the HSCCC-CPC columns may
be continuously monitored by a UV–VIS detector as in conventional
liquid chromatography.
• An important difference between these two methods is that HSC-
CC-CPC uses the liquid stationary phase which, if carried over from
the column, tends to disturb the tracing of the elution curve.
• Avoid trapping the stationary phase in the vertical fl ow cell
by eluting the lower mobile phase upward from the bottom;
do the reverse if the upper is used as the mobile phase.
• When the upper mobile phase is eluted from the top of the
fl ow cell downward, it is important to prevent the formation
of air bubbles which may become trapped in the fl ow cell and
disturb the tracing of the elution curve.
• Bubble formation can be largely avoided by degassing the
two phases in the separatory funnel before use, and also by
connecting fi ne PTFE tubing (typically 30 cm × 0.4–0.5 mm
i.d.) to the outlet of the monitor so that the pressure within
the fl ow cell is substantially increased.
13.5.1.11 Measurement of Stationary Phase Retention
• When the separation is completed, rotation is stopped and
the column contents are collected into a graduated cylinder
by connecting the column inlet to a nitrogen cylinder (ca.
50 psi; 1 psi = 6894.76 Pa).
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