MadSci Network: Botany

Re: in chromatography, does yellow appear before or after green?

Date: Sun Oct 22 12:42:21 2006
Posted By: David Hershey, Faculty, Botany, NA
Area of science: Botany
ID: 1161484670.Bt

Solubility is not the factor that determines why xanthophyll moves slower than
chlorophyll in chromatography. To move at all, the compounds being
chromatographed have to be soluble in the mobile phase. What determines the
speed of movement is the solid or stationary phase, which "slows" different
compounds to varying degrees and causes them to separate. 

The first reference discusses the Rf value, which is the distance a compound
moves divided by the distance the solvent front moved. An Rf of 1 would mean the
compound moved at the same speed as the solvent and would be at the solvent
front. An Rf of zero would mean that the compound did not move at all. In the
example in reference 1, the Rf value for chlorophyll a in the silica gel system
used was 0.59 but it was only 0.15 to 0.28 for the xanthophylls. The
xanthophylls did not move as far as the chlorophyll.

Tomato paste should not contain chlorophyll, unless it was made from green
tomatoes The main pigments in ripe tomatoes are carotenoids including lycopene,
a red carotenoid. The second website lists the chemical composition of a wide
variety of foods , however it only lists a few of the carotenoid pigments in
tomato paste.

The third reference used high pressure liquid chromatography (HPLC) and open
column chromatography (OCC) to separate cartenoids from tomato paste. They noted
the sensitivity of carotenoids to light, heat and oxygen. Perhaps the reason for
your faint bands was degradation by light, heat or oxygen, or perhaps your thin
plate system was not an efficient separation system for tomato paste. 

The OCC method produced 8 major carotenoid bands: lycopene, lycopene isomers,
gamma-carotene, zeta-carotene, beta-zeacarotene, beta-carotene, alpha-carotene
and phytofluene. Note that in OCC, the fastest moving compounds appear at the
bottom of the column because the solvent moves from top to bottom.

Search or other search engine for tomato chromatography to find more


Re: How do you identify pigments as they show up on paper chromatography?

USDA National Nutrient Database for Standard Reference

Analysis of carotenoids in tomato paste by HPLC and OCC

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