NP-40

NP-40 (Nonidet P-40) is a nonionic surfactant used in the isolation and purification of functional membrane proteins, consisting of "octyl phenol ethylene oxide" condensates and "nonyl phenol ethylene oxide" condensate complexes. NP-40 has a critical micelle concentration of 50-300 µM and an aggregation number of 100-155.

According to the Sigma-Aldrich catalog, NP-40 is no longer commercially manufactured and IGEPAL CA-630 is offered as a chemically indistinguishable (but not identical) substitute.