Abstract: Disclosed is a demountable tube for a plasma torch assembly, such as an ICP torch assembly. The tube includes an open tubular body for radially surrounding a plasma within the tubular body. The tubular body may comprise a wall; and a mounting feature projecting from the tubular body for at least one of: (i) controlling alignment of the tubular body with respect to a mounting portion of the torch assembly, and (ii) releasably securing the tubular body to a portion of the torch assembly. The tubular body may also have a transmission zone that is partially devoid of said wall and includes at least one hole through said wall. The tube may be opaque. A plasma torch and ICP spectroscopy system are also disclosed.