On tlc plate i get some colorful band under uv 360nm, like pink, brown, indigo, sky blue and some others. How can i tell that this color indicates this compound?
And in which extract hexane, chloroform,ethyl acetate,aqeous i go for flavonoids and phenolics
In TLC, we make a record of colour of bands under UV and when sprayed with reagents. As you indicated , we use 254 and 366 nm for short and longer UV band regions, respectively. Recording this helps you identify them when you are isolating the same compound again but this is a crude measurement as numerous compounds give you similar colours. The use of reagents also helps you to visualise compounds and, in some cases, such as vanillin/sulfuric acid, you get beautiful colours for the spots that you may also record. From reporting point of view, it is important to record the retardation factor (RF) value which is the distance travelled by your compound dived by that of the solvent. If you must report, this is more important for the solvent system you use. Remember that TLC appearance give very little information to ascertain compounds identity and you are expected to do other tests that characterise your compound – say spectroscopy and/or other more robust chromatographic methods (HPLC, GC or hyphenation methods).
For the flavonoids, the general misconception is that they are always polar. There are however many nonpolar flavonoids as well. Hence, you my extract some of them by hexane, some by chloroform, some by acetone and some by water… If you don’t know what you are looking for, extract them by alcohol as it gets out both polar and non-polar compounds. If you are working on biological activity, you may also extract them sequentially by the solvents of increasing polarity, test them for the activity and get the flavonoid or other compound from the active fraction.
Good luck …
Try to take a photograph, and print it in color. Save the photograph under a name that links the image to the project and extract.
Here's an overview of flavone compounds:
https://www.teledyneisco.com/en-us/liquidChromatography/Chromatography%20Documents/Application%20Notes/Purification%20Strategies%20for%20Flavones%20and%20Related%20Compounds%20App%20Note.pdf
Alternately you can scratch specific silica band add to suitable solvent and perform mass analysis, which will give you an idea of a specific compound and you can assign that colour band to the identified compound.
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