Alkaline Phosphatase assays, p-nitrophenyl phosphate stock soln.

[Altaf A. Wani]

For our Ap assay (mainly ELISA related) we dissolve PNPP at 1 mg/ml in 1 M
diethanolamine buffer, pH 9.5; 5 mM MgCl2.  You could prepare a stock
substrate solution and store it in cold as long as it does not turn yellow
over time due to hydrolysis. Best way is to prepare fresh before use. We use
prepacked 5 mg tablets from sigma and just add them to a 5 ml buffer
solution before assay. Good Luck.

Al Wani
Professor, Radiology
The Ohio State University