Nonidet P-40 is sometimes abbreviated as NP-40, but should not be confused with a different detergent by the same name NP-40, nonylphenoxypolyethoxyethanol of the Tergitol NP series of Dow Chemicals.
Nonidet was a trademark of Shell Chemical Co. from 1956 to the early 2000s,[1][2] but they no longer make it.
Sigma-Aldrich has replaced Nonidet P-40 with IGEPAL CA-630, which is described as a "nonionic, non-denaturing detergent".
Tergitol and the Sigma and BioChemica Nonidet P40 substitute detergents consist of nonyl-phenyl-polyethylene glycol.
The original Shell Nonidet P-40 consisted of octyl-phenoxy(polyoxyethylene)ethanol, making IGEPAL the most comparable of the four substitutes.