Good day everyone, I have met a problem in TLC whereby I can't find a solution. Most colleague told me to collect all samples of the spots formed to run analysis to determine which is my compound but is there any software to try out?
When I perform TLC chromatography, if there is more than 1 spots formed excluding the starting material, is there a method to determine which spot is likely the product formed?
Example in the photo attached, if the starting material is the green spot, blue and red are the likely products formed. I'm using normal phase silica gel tlc plate, so red is the more polar and blue is the least polar compound.
Is there a software to determine which compound is more or less polar so I can determine which spot is likely the product? Can I use Marvin Sketch to determine the polarizability or dipole moment calculation? The higher one should be the more polar ones.
Hi Lee Roy,
you can use the logP-value as an estimation of polarity of a molecule. logP-values correlate with the retention time / RF-value of a molecule. But be aware that the logP-value is only an estimation. logP values do not take into account intermolecular hydrogen bonds in molecules, for example. This can significantly change the polarity of a molecule.
Regards
Markus
You did not mention the stationary phase for the TLC. Most TLC is done using silica gel. If this is a silica TLC plate, then compounds moving higher on the plate are typically less polar than those that are more strongly retained and thus did not move as far up the plate.
As with reverse phase HPLC, the functional groups on the products and the solvent modifiers can have a dramatic impact on the retention of compounds.
If your product is an acid from hydrolysis of an ester, the product will be more polar than the starting material. However, if you are methylating a phenol, the product would be less polar and would move higher on the plate.
Thank you Leena Rao, I'm using hexane: Ethyl acetate solvent system but i not sure how to determine whether my compound is the more polar or less polar one compared to my starting material.
Thank you Markus Christ I'll check the logP value from Marvin sketch software.
Thank you Larry Hall I'm using normal phase silica gel tlc. My starting material is amine and my product is thiourea.
Thank you Mushtaq Ahmad . I'll look into the pdf.
Hello Lee
Rf in TLC measure in simple way by measuring the distance travelled by analyte/solvent front measured from where the analyte applied.
If you have x axis and Y axis value with your TLC plate applicator you can scan that plate on Camag scaner with wincats software where you can get Peak Rf value and Peak area also.
To calculate Rf value & %Area of peaks of tracks, you could try winCATs & videoscan or visionCATs of CAMAG
Hi Sharad Medhe Tung Thanh Nguyen , I'm actually more interested in determine which spots is more or less polar from the starting material by the structure of the compound because I want to purify my compound.
Left is my starting material while right is my product but there's 3 spots formed on the TLC plates.
if you are using silica as stationary phase and hexane :ethyl acetate as solvent system then the spot least traveled (red) may have the higher polarity then others. you can use marvin sketch chemdraw, acd chemsketch for calculation of log p.
Dear Shikha Sharma , ok noted. I will check the polarity of my compound via marvin sketch. This will ease the purification a lot. Thanks a lot.
Just keep in mind that not only polarity is the variable responsible for retention in chromatography. sometimes solvent interactions can tinker with retention, including reverse positions. Hope this helps
Ok noted. Hopefully my compound doesn't affect the polarity since it forms many spots. Thanks Moacir Brito
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