TLC

[pinkypig]

hi I’m a bit confused because i have done this thin layer chromatography experiment using different lipids and some of the lipids have given more than one spot but i can't figure out why? Does any one have any idea?

[pinkypig]

Also some of the spots start off big then get smaller as they go further up? what does this indicate?

[mith]

more than one substance/contamination/isomerism.

[pinkypig]

yeh i was thinkin along the lines of isomerism,but how bout some of the spots which start off big then get smaller as they go further up??

[mith]

You mean the spot is teardrop shaped? Probably not important unless you can see that they are really two spots mushed together(suggests greater separation needed-different solvent systems etc).

[pinkypig]

Also would there be a difference in the appearance of the spots on the chromatogram if they were due to contamination or if they were due to isomerism?

[mith]

Well, each spot is a different substance. The Rf value gives you some idea of what it is. You should already have an idea in mind of what substances are present(identity, relative polarities etc). If a spot doesn't fit in with your prediction then either your prediction didn't account for it or you have a contamination.