Extraction Technologies For Medicinal And Aromatic Plants - Unido

EXTRACTION TECHNOLOGIES FOR MEDICINAL AND AROMATIC PLANTS
ii) 2–3 ml/min for a semi preparative column with 1.6 mm i.d.
PTFE tubing (800–1000 rpm) (up to 500 mg sample load);
iii) 1 ml/min for an analytical column with 0.85–1.0 mm i.d.
PTFE tubing (1000–1200 rpm) (up to 50 mg sample load).
• These fl ow rates should be modifi ed according to the settling
time of the two-phase solvent system as well as other factors.
When the settling time is around 20 s and the K value
of the analyte is small, a lower fl ow rate is recommended.
13.5.1.7 Revolution Speed
The optimum revolution speed (revolution and planetary rotation
speeds are always same) for the commercial HSCCC-CPC instrument for
preparative separation ranges between 600 and 1400 rpm.
• Use of a lower speed will reduce the volume of the stationary
phase retained in the column, leading to lower peak resolution.
• On the other hand, the higher speeds may produce excessive
sample band broadening by violent pulsation of the column
because of elevated pressure.
13.5.1.8 Filling the Column with the Stationary Phase
• In each separation, the column is fi rst entirely fi lled with the
stationary phase.
• Before introducing the stationary phase, the column may be
fl ushed with a column volume of a solvent miscible with the
two phases used in the previous run (e.g. ethanol or methanol)
to wash out materials remaining in the column.
• This will also ensure a stable, clean baseline before the solvent
front emerges.
• Avoid trapping the air in the column, especially in a preparative
column. This can be easily tested as:
i) If no air is present in the column, the fl ow from the column
outlet is ceased shortly after stopping the pumping.
ii) If the solvent keeps fl owing from the outlet for more than
several seconds, the air trapped in the column should
be eliminated by resuming the pumping of the stationary
phase under low speed column rotation (100–200 rpm)
in a tail to head elution mode to accelerate air movement
toward the outlet of the column.
13.5.1.9 Sample Loading
There are two ways to load samples; both are satisfactory for
HSCCC-CPC separations:
• In the fi rst method, the column is entirely fi lled with stationary
phase and this is immediately followed by sample injection.
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