Microfluidics has been wildly used in many applications, especially in biomedical engineering. Liposomes are tiny vesicles made out of the same material as a cell membrane, and these particles can be filled with drugs to be used in drug delivery systems. The main objective of this research is to investigate the mass transfer between phases, lipid and water phase, in a passive micromixer specialized for liposome production. Here, a set of numerical models are generated in COMSOL Multiphysics software. Two interfaces, namely Laminar Fluid Flow and Transport of Diluted Species, are utilized in order to determine the mass transfer in this Toroidal micromixer. The mass transfer flux along the channel length is considered as the criterion of the analysis and the data obtained from simulations are plotted. The simulations are performed for different flow rate ratios (FRR: the ratio of water flow rate to lipid flow rate) and the results are compared. It was observed that for low FRRs, the flux drops suddenly at the middle of the micromixer, which may result in an increase in the outlets' heterogeneity in terms of the liposome size. Moreover, it is observed that increasing FRR results in a decrease in the convective mass transfer in the micromixer. Finally, a method is proposed to precisely control this system by using Flow Cytometry.