Mobile phase gradient generation microfluidic device

A method for separating the components of a fluid sample, comprising:

• (a) providing the microfluidic device comprising
• a substrate having a microchannel formed in a surface thereof;
• a cover plate arranged over the substrate surface, the cover plate in combination with the microchannel defining a separation conduit for separating the components of the fluid sample according to a specific component property, wherein the separation conduit has an inlet port and an outlet port;
• and
• an integrated gradient-generation means for generating a gradient of a selected mobile-phase component in a mobile phase by the use of pressure driven flow, including a mechanical switching structure adapted to allow the mobile phase from the gradient-generation means to be transported through the inlet port into the separation conduit and out of the outlet port;
• (b) using the integrated gradient-generation means to generate a gradient of the selected mobile-phase component in the mobile phase,
• (c) controllably introducing a predetermined volume of the fluid sample from a sample source into the separation conduit;
• and
• (d) conveying the fluid sample through the separation conduit using a mobile phase, thereby separating the components of the fluid sample.