Diffusiophoresis, i.e. the movement of macromolecules along a molecular gradient, is shown to be an efficient means to drive particles in microchannels. By using a generic microfluidic setup, we assess the displacement of silica particles under a controlled salt gradient and provide experimental evidence for a strongly enhanced migration process, the amplitude of which depends on the nature of the salt. A theoretical description shows quantitative agreement with the observed experimental features. Furthermore, we describe a set of microfluidic operations such as separation, sorting or focusing of a colloidal assembly which can be efficiently performed using diffusiophoresis.