I recently purchased a bottle of 97% purity ricinoleic acid (fatty acid of castor oil) and also have two others from different vendor sources (all are from China). For some reason, they all show three streaked spots on the TLC stained by KMnO4. I understand that ricinoleic acid has an isomer but I am unsure if it is the reason.
HNMR suggests it is indeed ricinoleic acid, but when I ran a reaction with an epoxy, I ended having 4 - 6 more spots after the reaction. This makes further synthetic work difficult due to the sheer amount of highly adjacent spots to isolate by column chromatography.
it may be because of the derivatives of the compound. u may need to purify it before proceeding
Try purchasing 99+% Ricinoleic acid from Nu-Check Prep http://www.nu-chekprep.com/ page 8 of their catalog see link.
http://www.nu-chekprep.com/catalog.pdf
In similar analysis with different compounds I have experienced the appearing of the isomers by TLC. I've tried two things: derivatize the one I wanted to "separate" them from the others, and in a separate batch "purify" the analite by SPME with an adequate cartridge.I really can´t remember the details but it was not ricinoleic acid though.
Good luck!
Thank you for the answers. I suspect i will have to resort to painful purification work, nonetheless.
Try running on GC-MS; I see you have a core facility which could be very helpful. https://bsyse.wsu.edu/acsc/equipment/
I have encountered similar problems with isomers many times + fatty acids are often methylated - did you by any chance have methanol in the TLC mobile phase? If so, try substituting ethanol or IPA and see if one of the spots disappears. EtOH and IPA are both more non-polar than MeOH so reduce the % and you can probably get similar TLC migration.
@ Timothy C Morton:
Yes, I did GC-FID and found out that.... it is quite a mess... I think it explains the TLC results. I found one huge peak and three other outstanding peaks among a thousand other miniscule peaks.
We just haven't purchased the high grade (99.99%) standard to use as reference yet. But Thank you for the suggestion.
I normally use DCM/EAc or Hexane/EAc.
The problem then remains in how I can effectively purify a batch of 50 grams in a column to make materials.....
If you use GC-MS then you'll know what the 3 main peaks other than Ricinoleic might be. You may have some degradation/oxidation products there in addition to the trans form, but they should be easy to remove.
"Overview of Methods for the Determination of trans Fatty Acids by Gas Chromatography, Silver–Ion Thin-Layer Chromatography, Silver–Ion Liquid Chromatography, and Gas Chromatography/Mass Spectrometry" (+ another article in that issue). Author: Nimal Ratnayake, W.M.
Source: Journal of AOAC International, Volume 87, Number 2, March 2004, pp. 523-539(17)
This paper notes the use of silver nitrate in TLC or column form can separate cis/trans isomers. And the following is a note on how to make your own silver nitrate plates but they are commercially available.
http://lipidlibrary.aocs.org/Analysis/content.cfm?ItemNumber=40353
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