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Continued from this question. I purchased new triethylamine from Sigma Aldrich, spotted freshly opened triethylamine to the TLC plate, dipped into ninhydrin solution, and heated it. Again the purple spot showed. The ninhydrin solution seems to have no problem because there were no purple spots when I treated it with empty TLC plates. I have used ninhydrin staining using eluent containing the triethylamine before (TLC monitoring of Buchwald-Hartwig coupling reaction using ninhydrin stain), but there was no problem. I don't know why. Also in one site, it says that staining with ninhydrin shortly after eluting with 1% triethylamine is one of rookie mistakes in TLC. Is staining with ninhydrin 'shortly' after eluting with triethylamine the problem? Should I wait a minute after developing the plates with the eluent containing triethylamine? How can ninhydrin detect the triethylamine which is a tertiary amine?

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  • $\begingroup$ When you have a lot number you can access Certificate of Analysis on Sigma. How pure is TEA? Someone answered it earlier stating that TEA might be impure. Just out of curiousity, do you have access to an HPLC that can be used for reaction monitoring? If your compounds somewhat are hydrophobic and soluble in ACN or MeOH, a C18 column should be able to separate most of the organic compounds $\endgroup$
    – AChem
    May 3, 2022 at 4:54
  • $\begingroup$ @Achem I thought that he or she is saying that the TEA is corrupted during storage. So I thought that there would be no problem with fresh TEA. Unfortunately our lab doesn't have HPLC. $\endgroup$
    – Krang Lee
    May 3, 2022 at 4:57
  • $\begingroup$ Okay, still access the CoA from Sigma by entering the lot number (written on the bottle) and see how pure is TEA. The person who responded earlier is saying that TEA is not pure as received. It does not degrade during storage. $\endgroup$
    – AChem
    May 3, 2022 at 4:58
  • $\begingroup$ @AChem The CoA says that the purity of triethylamine is ≥99%. $\endgroup$
    – Krang Lee
    May 3, 2022 at 5:10
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    $\begingroup$ Does this answer your question? Does ninhydrin staining detect triethylamine? $\endgroup$ May 3, 2022 at 11:51

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