???Thinlayer Chromatography/Caffeine????

[mozart_fan]

Im sure this is a very common lab in ochem. I just got my report back. We used thin layer chromatography to asses the purity of caffeine we extracted and sublimed.

My TLC plate had three things:

"pure caffeine" provided....the caffeine I extracted.....and the remaining crude caffeine i had/impure with chlorophyll....

Of course our lab manual is horrible at explaining things...i dont understand why the Rf value for pure caffeine is LOWER than the crude caffeine. The crude caffeine contains more chlorophyll than the pure...and chlorophyll is more polar so should bind the the plate more resulting in a lower Rf.

Wht does pure caffeine have a lower Rf than crude caffeine? I thought it would be the other way around.

I

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[byeh2004]

ughhh i had to do one this week for tetraphenylphorine 👎 👎 👎

 

[SBBunny]

Look at the structure of chlorophyll, what does the long hydrocarbon side chain tell you?

 

[BMW M3]

Look at the structure of chlorophyll, what does the long hydrocarbon side chain tell you?

I know it tells me that maybe i should reconsider my decision to apply to med school!! 😱

 

[Dave_D]

Of course our lab manual is horrible at explaining things...i dont understand why the Rf value for pure caffeine is LOWER than the crude caffeine. The crude caffeine contains more chlorophyll than the pure...and chlorophyll is more polar so should bind the the plate more resulting in a lower Rf.

Wht does pure caffeine have a lower Rf than crude caffeine? I thought it would be the other way around.

I

Quick question for you, do you know what adsorbent you're using?

 

[Dave_D]

Also are you sure caffeine is more polar?