Devices and methods are described for separating components in a sample, for example a protein sample, in a branched channel structure, using flow barriers to separate flows between channels and/or providing an interface with an analysis device such as a mass spectrometer. In one example, a flow barrier is provided between a main (4) and a branch (12) channel to reduce diffusional contamination between the channels and cross talk. In another example, contamination of components entering the analysis device is reduced by switching selected components from a main channel (4) into a branch channel (12) and then through an interface into the analysis device.