Chromatography systems and methods using them

A microfluidic device comprising:

• a laminated wafer comprising an internal microchannel formed from laminating individual metal layers to each other, the laminated wafer comprising a first port, a second port and a third port each fluidically coupled to the internal microchannel, wherein each of the first port, the second port and the third port permits fluid flow into and out of the internal microchannel;
• and
• a bypass restrictor that fluidically couples at least two of the first port, the second port and the third port to each other and is configured to restrict fluid flow.

A laminated wafer microfluidic device configured to provide a received sample to a plurality of different ports of the laminated wafer microfluidic device depending on a gas pressure within the laminated wafer microfluidic device, wherein the laminated wafer microfluidic device comprises an internal microchannel and an external fluid connection that fluidically couples at least two ports of the laminated wafer microfluidic device, and wherein the laminated wafer microfluidic device comprises a sample inlet port fluidically coupled to the internal microchannel and at least one switching gas port fluidically coupled to the internal microchannel, the switching gas port configured to provide a gas into the internal microchannel to control the gas pressure within the laminated wafer microfluidic device to direct flow of the received sample.