On-line precolumn photochemical generation of pH gradient: micro-high-performance liquid chromatography of methotrexate and its impurities

LED controlled flow photolysis for concentration gradients in microfluidic systems

Many of the channels and reservoirs in microfluidic systems are used simply to allow liquids with different compositions to be delivered to where they are needed. An alternative approach is to use dissolved photochemicals and variable intensity LEDs to generate composition changes in situ. We applied this approach to generate concentration gradients of HCl for gradient ion chromatography.