Flow method and apparatus for screening chemicals using micro x-ray fluorescence. The invention includes a method and apparatus for screening a mixture of potential pharmaceutical chemicals for binding to at least one target binder. According to the method, after preparing a solution of potential pharmaceutical chemicals with at least one target binder, the solution is flow-separated into at least two separated components. Each component is exposed to an x-ray excitation beam. Any component that emits a detectable x-ray fluorescence signal is isolated.