Microfluidic devices, systems and methods for performing integrated reactions and separations

A method of detecting the effect of a third analyte on the interaction between a first and a second analyte, the method comprising:

• contacting a first analyte and a second analyte with at least one third analyte in a first microfluidic channel portion having substantially no electric field applied across its length, wherein the first analyte and the second analyte interact to produce a product;
• transporting at least a portion of the first analyte, second analyte and product to a second channel portion that is in fluid communication with the first channel portion and which has an electric field applied across its length;
• detecting a difference in the electrokinetic mobility of the product relative to at least one of the first and second analytes, the difference in mobility being indicative of an effect of the first analyte on the second analyte;
• and,
• measuring a change in the electrokinetic mobility of the product in the presence of the at least one third analyte relative to a change in the electrokinetic mobility of the product in the absence of the at least one third analyte.