Arsalan Daudi Author Answered Sep 28, 2014
University of California
I wouldn't expect a white precipitate. Could something be precipitating in the buffer from before? Incomplete acidifying of the DAB has led to light brown precipitation in our hands. If that is what you're seeing, a low level of that should not affect the experiment. In addition to this, I have posted an update in the comments above. After publishing this protocol, I realized that using the DAB tetrachloride salt prevents the need for the acidification step. With this, I never saw any DAB precipitation again. Such search for 3,3'-Diaminobenzidine tetrahydrochloride (the one by Santa Cruz sc-209686 works fine - I'm quite sure the one from Sigma will be fine too).