Transfer of fluid substances, and/or substances comprised in fluid substances, is controlled by introducing a separation medium, which prevents transfer of the fluid substances, and/or the substances comprised in the fluid substances, to an intermediate cavity connecting a first cavity and a second cavity; and introducing a connection medium to replace the separation medium and thereby start substance transfer to the second cavity. Substance transfer may be readily controlled without relying on mechanical means. Based on the present invention, two-dimensional electrophoretic analysis can be readily implemented on a chip.