Abstract: A fluid-handling optical system such as a light-pipe assembly of a GC/FTIR apparatus includes a light pipe 10, preferably of gold, surrounded by a body 9. The body is of a material where the linear thermal expansion coefficient differs very little from that of the pipe 10. Thus they can sealingly abut a non-resilient end abutment, e.g. involving a gold disc 4.

Abstract: A spectroscopy cell has a body with a central outer sample chamber (6). Within this chamber (6) is a sample cavity (25) as part of a temperature controlled sample probe (23). At one end this sample cavity (25) is delimited by a movable gas connection insert (20) which extends outwardly to a temperature-controlled (e.g. cooled) end plate (8). Gas inlet and outlet tubes (29,30) also extend from the end plate to the sample cavity (25). In use the sample cavity (25) may be at a high temperature so that (a) it is difficult to provide seals for the gas connection insert (20) and gas tubes (29,30); and (b) they are subject to considerable thermal expansion and contraction. Similar problems occur with very low cavity temperatures. Therefore compressible seals (21,31,32) are provided in the end plate (8), remote from the chamber.