Page 131 - phytochemistry general program

Radioactivity .3

Radiochromatograms may be analyzed with special scanners. Alternatively, the
distribution of radioactivity may be determined in small zones that are scraped
off the layer using a zone scraper. The radioactivity is determined using liquid

scintillation counters.

B- Quantitative TLC after elution

Equal known volumes of the test solutions are spotted, alongside with three known
standard solutions. Plates are developed and visualized, usually non-destructively.
Zones containing the spots are scraped, eluted with suitable solvent(s) and
evaporated. Then determined according to the nature of the solute by one of the

following methods:

Gravimetry. 2- Ultraviolet spectrophotometry. 3- Fluorimetry. 4- Colorimetry .1
after chemical reactions

Modern Thin-Layer Chromatography

Modern thin-layer chromatography is a powerful reliable and cost efficient method
for qualitative and quantitative analysis. Synonyms - Planar chromatography -
Instrumental thin-layer chromatography - High performance thin-layer
chromatography (HPTLC). “HP” stands for “high performance”. This is not a very
good choice, because the conventional TLC layers are not “Low performance”

provided they are combined with appropriate instruments and techniques.

HPTLC has become the accepted term for layers which:

·Are slightly thinner than conventional layers (0.20 mm instead of 0.25 mm), and
thus need less sample to show the same measuring results.

·Have a smaller mean grain (7 µm instead of 12-20µm) and in particular a closer
grain size distribution than conventional layers.

·Give a better resolution with a migration distance about 50% shorter.

·Have improved optical properties over conventional layers which give better
accuracy during densitometric evaluation.

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