|MadSci Network: Chemistry|
Daniele, I think that there are a number of reasons that you see no separation, but I'd need more information to give a complete answer (What type of paper did you use and what was your solvent. I'm going to assume that you used water.). 1) In the case of the marker, it is possible that only a single dye is being used, so that no separation would occur (the dye could not separate from itself). 2)In the case of the drink mix, which probably does contain more than one dye, there are a number of reasons for a lack of separation. a) In order for separation to occur, the solubilities of the dyes in water must differ significantly. If they don't, there will be little separation. b)The length of your paper may need to be increased. This may allow for some separation, as long as solubility differences are large enough. c)You may need to get special paper (Thin Layer Chromatography or TLC paper). There are a number different types of TLC paper. I'd try one coated with ODS (octadecylsilane). d)You may need to change your solvent. If you haven't tried it yet, try methanol by itself or mixed 50-50 with water. Lastly, if this doesn't work and you have access to the apropriate items, try this: a) Mix hexane with confectioner's sugar to form a thin, pourable mixture. b) Pour this mixture into a long glass tube with a stopcock on the end (a buiret would work nicely). c) Oh yeah, put some glass wool into the biuret FIRST to keep the mixture from coming out when you open the stopcock. d) Let some of the hexane drain out through the open stopcock, but don't let the sugar mixture become dry (keep adding hexane to the top) e) Drip your dye into the biuret on top of the sugar/hexane mixture. f) When the dye soaks into the sugar just a little, add more hexane. This column should separate your dyes. Have fun!
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