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
be known beforehand, the photodiode array detector is useful, especially
when constructing profi les of plant extracts. The fi ngerprint profi le of plant
extracts can be used for identifi cation purposes and also for obtaining semiquantitative
information if the sample preparation was not done for quantitative
analysis. Similarly, the profi le can be generated for the fi nished product
and used to record batch to batch variations. The fi ngerprint profi le can be
used to study changes in the composition of the fi nished product or, in other
terms, to indicate the stability of the product.
The most important use of HPLC is in estimation of markers in
plant drugs. The steps in HPLC analysis are fundamentally the same as used
for any other analytical technique. The response of the test sample is compared
to that of a known quantity of the marker to quantify the marker in the
test substance. The HPLC method is developed from knowledge of the technique
and chemistry of the marker. In chemical analysis, HPLC has no parallel
and can be customized to produce the most precise and accurate results. The
HPLC analysis is vital in the analysis of a finished product and the expected
results are superior to those from TLC, as the separations in HPLC are better.
However, run time of HPLC analyses usually varies from 15 to 30 min, which
restricts its use if large numbers of samples are to be analyzed.
14.6 TLC versus HPLC
TLC has emerged as a major tool in standardization of plant
materials. The advancement and automation of the technique has made it a
fi rst choice for plant drugs. Its use has become more popular in developing
countries where advancements of HPLC are not cost effi cient. TLC offers
several advantages over HPLC. Sample and mobile phase preparation do
not require elaborated steps of purifi cation, degassing, and fi ltration, which
are essential to protect expensive columns from deterioration. Several samples
(up to 18) can be accommodated on a single 20 x 20 cm 2 plate. The
test samples and standards are analyzed simultaneously under the same
conditions. Several analysts can work simultaneously as each step in analysis
is carried out independently using separate equipment. The choice of
solvent systems is unlimited, unlike for HPLC where column chemistry disallows
the use of extremes of pH in mobile phase. The technique allows enormous
fl exibility of derivatization with chromogenic spray reagents, making
possible the detection of an analyte that is transparent to ultraviolet light.
It also allows multiple evaluations of the developed chromatogram, which
is not possible in HPLC. There is no leftover from the previous analysis to
interfere in the next, as each time a fresh plate is employed. Lastly, it saves
tremendously on the time and cost of the analysis.
TLC offers many advantages but also has some disadvantages.
It fails to match the sensitivity of HPLC and has not kept with the pace
of developments and advancements happening in the area of HPLC. TLC is
258