The chemical weapon in question is sarin gas. While not nearly as deadly as later nerve agents like VX, Dexter is shown to suffer massive exposure, He would have to be hospitalized immediately for quite some time and receive heroic treatment to survive.
At 41:56, Dexter and Deb are drinking Negro Modelo beers and Dexter opens the twist off cap. Negro Modelo bottles are not twist off. There are no threads visible when Dexter hands the bottle to Deb.
At 17:08, the EMT refers to "...this gas...", meaning the Sarin, although there is no way to identify Sarin gas without a laboratory. It is odorless, tasteless and colorless.