Sodium dodecyl sulphate (SDS) is not a nonionic detergent. It is an anionic detergent.

Here's why:

* Anionic detergents have a negatively charged head group. SDS has a sulfate group (SO₄⁻²) which is negatively charged.

* Nonionic detergents have no charged head groups. They are typically based on long hydrocarbon chains with hydrophilic groups like polyethylene glycols.

So, SDS, with its negatively charged sulfate group, falls into the category of anionic detergents.