Q：I always thought that Nonidet P40 and Triton X-100 are in fact different > trademark names of the same detergent. Now I found couple of protocols > for cell lysis which call for both NP40 and TX-100, each at 1% conc. > Now I started wondering, may be I was wrong all the time? Could anyone > shed some light on this? A：The Shell product Nonidet P40 is octylphenoxypolyethoxyethanol, which is the same name given to Triton X-100, a trademark of Rohm and Hass or Union Carbide depending on the bottle you look at. The two products are close to identical although the "polyethoxy" in the two is not precisely the same. Because Nonidet P-40 is no longer available Sigma now refers you to Igepal CA-630 which they claim is chemically indistinguishable from Nonidet P-40 (and note they do not point you to Triton X-100).
NP-40 on the other hand is really Tergitol Type NP-40, a solid at room temperature, and chemically nonylphenoxypolyethoxyethanol. I suspect that many people sloppily refer to Nonidet P-40 as NP-40 (or Nonidet NP-40) but this is not correct. Add to this mess the other nonionic detergents Brij and Tween (which are chemically distinct from each other and Triton, Tergitol and Nonidet) and you've got a recipe for serious confusion.
If the paper you're following mixed Triton X-100 and Nonidet P-40 then I can't imagine that substituting Triton alone would make any difference. If the second detergent is really Tergitol NP-40 then it might make some small difference.