Direct analysis of intraparticle mass transfer in silica gel using single-microparticle injection and microabsorption methods

Sorption and desorption processes of cationic dyes occurring in single silica gel microparticles in an aqueous solution were kinetically studied by microcapillary manipulation/injection and microabsorption methods. The sorption and desorption rates of rhodamine 6G were limited by diffusion of the dye in the particle interior. For methylene blue, the desorption rate was slow compared with the sorption rate, and the rate-determining step was not the diffusion of the dye. The sorption and desorption processes of the dyes were discussed in terms of intraparticle diffusion as well as of that accompanied by slow desorption.