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Does ninhydrin staining detect triethylamine?
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Ken Paul
Does ninhydrin staining detect triethylamine?
You are right that tertiary amines like triethylamine will not react with ninhydrin in the typical thin layer chromatography (TLC) staining conditions. However, when you use triethylamine as received it will not be 100 % pure. Triethylamine is prepared by alkylation of ammonia. As a result, it usually contains small residues of ammonia and partially alkylated derivatives. These can react with ninhydrin, giving a stained TLC plate. Therefore, I suspect that what you see results from impurities in your triethylamine.
You are right that tertiary amines like triethylamine will not react with ninhydrin in the typical thin layer chromatography (TLC) staining conditions. However, when you use triethylamine as received it will not be 100 % pure. Triethylamine is prepared by alkylation of ammonia. As a result, it usually contains small residues of ammonia and partially alkylated derivatives. These can react with ninhydrin, giving a stained TLC plate. Therefore, I suspect that what you see results from impurities in your triethylamine.
Seems probable if ammonia is formed during storage after purchase. But in the website I linked, it is written that staining with ninhydrin shortly after eluting with 1% TEA is common mistakes. I think the website is saying that there is another problem other than the impurities. Is the staining 'shortly' after eluting problem?More
You are right that tertiary amines like triethylamine will not react with ninhydrin in the typical thin layer chromatography (TLC) staining conditions. However, when you use triethylamine as received it will not be 100 % pure. Triethylamine is prepared by alkylation of ammonia. As a result, it usually contains small residues of ammonia and partially alkylated derivatives. These can react with ninhydrin, giving a stained TLC plate. Therefore, I suspect that what you see results from impurities in your triethylamine.
Since you did not have the problem before in one of your previous questions (TLC monitoring of Buchwald-Hartwig coupling reaction using ninhydrin stain), impurities may also have been introduced in the meantime by uncareful usage of the bottle.
You are right that tertiary amines like triethylamine will not react with ninhydrin in the typical thin layer chromatography (TLC) staining conditions. However, when you use triethylamine as received it will not be 100 % pure. Triethylamine is prepared by alkylation of ammonia. As a result, it usually contains small residues of ammonia and partially alkylated derivatives. These can react with ninhydrin, giving a stained TLC plate. Therefore, I suspect that what you see results from impurities in your triethylamine.
Since you did not have the problem before in one of your previous questions (TLC monitoring of Buchwald-Hartwig coupling reaction using ninhydrin stain), impurities may also have been introduced in the meantime by uncareful usage of the bottle.
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