Abstract An experimental technique to follow sorption kinetics under constant volume-variable concentration conditions is described. The system consists of a sampling and a sorption vessel both separated by an electro-pneumatically driven valve with known characteristics. Analyzing the gaseous phase above the sorbent by mass spectroscopic multiple ion detection, uptake curves of single components and binary mixture sorption are registered. Valve effects, conductance of the whole system and wall adsorption must be corrected by blank experiments. Equilibrium and non-equilibrium data for benzene and ethylbenzene and for their binary mixtures on silicalite-I are reported.