|MadSci Network: Botany|
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 google.com or other search engine for tomato chromatography to find more info. References 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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