Phenolphthalein diphosphate tetrasodium salt (CAS# 68807-90-9) is a phenolphthalein (P318010) derivative used as a diagnostic compound for the determination of phosphatase, such as in sour milk cheese. Phenolphthalein diphosphate tetrasodium salt has also been used in the separation of deoxyribonucleic acid from ribonucleic acid without the use of enzymes. Dyes and metabolites.