The ZLC method is a simple and rapid approach to measure adsorption equilibrium isotherms. When extending this technique to the measurement of large concentration steps, the primary problem is how to estimate the outlet flowrate from the measured concentration signal. In this paper, two different corrections to calculate the outlet flowrate are introduced. Based on simulations of the ZLC system that are in good agreement with reported experimental results, a series of desorption cases were simulated. Isotherms were calculated using the two approximations of the outlet flowrate. The comparisons are used to identify the range in which the approximations are applicable. Darken's thermodynamic correction factors were also calculated to verify the validity of the flow corrections.