Extraction Technologies for Medicinal and Aromatic ... - Capacity4Dev

14 QUALITY CONTROL OF MEDICINAL AND AROMATIC PLANTS AND THEIR EXTRACTED PRODUCTS
BY HPLC AND HIGH PERFORMANCE THIN LAYER CHROMATOGRAPHY
and deliver. The precision and accuracy, as known to the author from personal
experience, is fairly high after a short experience. The semi-automatic application
uses devices such as Linomat 5 from Camag and Applicator AS 30 from
Desaga, which use a syringe that has to be manually cleaned and filled. The
remaining part of the application is automated through computer commands.
The solution is applied as a spot or band of predetermined size at predetermined
points by touch and delivery or spray-on technique. The needle touches
the surface of the adsorbent layer and delivers, whereas in spray-on technique
the predetermined volumes are sprayed onto the plate. In the fully automated
application, all steps are controlled through a computer including washing of
the delivery line.
The typical concentration of the applied samples ranges from
0.1 to 1 mg/ml for qualitative analysis but is usually much lower for quantitative
purposes, which further depends on the molar absorption of the marker.
The typical volume for spot application is 1-5 μl, and 10 μl for band application.
These volumes are drastically reduced in HPTLC plates or ultrathin TLC
plates. Bands are known to give better resolution and results than spots, as
a narrow band is better suited to the optics of the TLC scanner.
14.4.6 Developing the Chromatogram
Development of plates is carried out in chambers which are special
purpose jars or simple containers good enough to hold the solvent in an
air-tight environment. There is no doubt that special purpose chambers produce
better chromatograms. Twin-trough chambers allow use of another mobile
phase in the chamber for the purpose of saturation, besides consuming smaller
quantities of solvent. The cost of the chamber, which seems high in the beginning,
is recovered by way of savings on the quantity of expensive solvents. Presaturation
of the chambers decreases R f values and corrects side distortions
of the solvent front. The plate is placed as nearly vertical as possible in the
chamber, ensuring that the points of application are above the surface of the
mobile phase and the sides of the plate do not touch the container walls.
The developing chamber should always be kept out of direct
sunlight. It should be protected from light during development, if the components
being investigated are suspected to be unstable. If sun rays fall directly
on the developing chamber, they may be refracted to different degrees
through the glass walls, producing areas of high temperature on the plate
and resulting in erratic fl ow of the mobile phase.
The technique of development has been largely improved in
horizontal developing chambers and completely automated in automated
development chambers or automated multiple development chambers.
However, the cost of this equipment (except for the horizontal development
chamber) is excessively high.
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