So, BET instrument can perform this test . Can i measure any gas other than nitrogern, argon, CO2 and Xe? Is it going to measure multilayer adsorption?
Yes, everything is virtually possible, including condensable vapours. The adsorption temperature just needs to be adjusted correspondingly. Any BET instrument will allow doing what you want, but also note that TGA instruments may do the same for gases which can be adsorbed at room temperature (or a bit lower of higher), e.g. CO2, H2O, etc. The accuracy will depend on the surface area, which needs to be high enough for measuring something.