[amexya]

I'm doing an organic chemistry lab report right now for the isolation of caffeine, and I cannot for the life of me figure out the answer to a few of the questions.
We used a UV light to see the analyte spots of the colorless compounds we tested.. it asks whether or not every compound can be seen using this method. I said that not every compound can be seen; only ones with a chromophorm can. I'm not sure if this is actually correct. Doesn't make much sense to me since my lab instructor doesn't explain much, if anything.
My second question relates to the first. It asked if my product (purified caffeine) was actually impure and contained sodium carbonate, would that be detected by TLC/show up under the UV light? I'm assuming that's a no as well, but I have nothing to back that up with.
I've researched both of these for about an hour now and I cannot find anything. If anyone knows the answers to these/could explain them a bit, that'd be great!
Thanks

[Arkcon]

Your first answer, that a molecule requires a chromaphore to be visualized by UV illumination, is a correct statement.  It may not apply in this case.  Question:  Did you observe the TLC plate before you ran an analysis?  For that matter, what did the TLC plate look like under UV?  If the TLC media on the plate has a fluor mixed in, it will glow without spats, and any non-glowing spots will appear as dark patches.  So if you saw that, your answer, although technically correct, won't apply.

In the second question, you're worrier about the sodium carbonate impurity.  What do you know about chromatography that can help you with this concern?  Also, you correctly knew about te need for a chromaphore previously -- what is a chromaphore?  Does caffeine have one?  Does sodium carbonate have one?

[fledarmus]

Do you have some sodium carbonate anywhere? If so, spot some on a TLC plate - can you see it under UV light?

I had one primary research investigator tell me that 15 minutes in the library could save me four hours in the lab, and another tell me that 15 minutes in the lab could save me four hours in the library. I think in this case, the lab wins out.