Extraction Technologies for Medicinal and Aromatic ... - Capacity4Dev

EXTRACTION TECHNOLOGIES FOR MEDICINAL AND AROMATIC PLANTS
It is always important to optimize the small-scale separation
(which will signifi cantly impact on throughput), the size of packing material
and the column needed to obtain the desired throughput, the mobile solvent
and the instrument capability. Normal-phase methods are the fi rst choice
because: direct transfer from normal-phase thin-layer LC or HPLC to prep-LC
is possible; costs of RP packing materials are still high; cleaning normalphase
silica is easier because the material is more robust; removing organic
solvents typically used in normal-phase chromatography from the fi nal product
solution is easier than removing water from an RP chromatographic fraction
and can be achieved at lower temperatures and provides higher product
quality and lower energy costs. Particle size of the stationary phase material
also plays an important role in the isolation of the desired compounds. The
choice of 5-μm particle size in a preparative column is not practical because
it not only increases the column pressure but also is extremely expensive.
Moreover, when the sample amount is increased, resolution performances
of 5-μm and 15-μm particles are not different.
11.4 Practical Consideration in Preparative HPLC
Scale-up
11.4.1 Sample Loading
If the tests on analytical columns with analytical loadings show
good separations, a scale-up to a larger column diameter can be performed
on prep-HPLC. Instead of jumping directly to the largest column diameter,
stepwise scale-up should be done. The fi rst step in the scale-up process is
the transfer of the analytical separation procedure to a 5 cm i.d. preparative
LC column. Optimization in a preparative column is required. The sample
injected onto the column usually starts at 1 g and increases to as much as
20 g, depending upon the quality (resolution) of the separation achieved,
the quality of the initial material, and the specifi cations for the pure product.
Start with the 1-g injection, collect fractions and re-analyze them for purity
using the analytical method, because with an increase in sample loading
there is a decrease in resolution.
(A) Scale up factor for column size = (Diameter prep) 2 x Length prep
(Diameter anal ) 2 x Length anal
(B) Flow rate (prep) = Flow rate (analytical) x (Diameter prep) 2
(Diameter anal ) 2
(C) Gradient duration (prep) = Gradient duration (anal) x = Length anal
Length prep
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