[smghz]

So twice in a row I was attempting to do solid-state peptide synthesis. When trying to couple just the first two amino acids, I performed the Kaiser test to ensure that the amines are protected by Fmoc. But while the beads were colorless, the solution turned deep blackish-blue-purple like color.

What are common reasons attributed for such failures? I fear that I might redo the entire experiment again, but I'd like to know what are the mishaps that can block (virtually) complete coupling. thanks.

[phth]

There needs to be no water, or the reagents will not work.  There needs to be enough reagents for complete amidation.  The amino acids added can get stuck in the resin if you do not do the procedure correctly.  In short, it could be alot of things  First I would try to wash more and see if the color persists in intensity.  It should decrease over time.  It will eb a good way to figure out how to do it if you don't know.