(A). Next, sample is injected and transported downstream (B), where beads with a suitable bioligand ion exchange group or or C-18 group have been retained. The target analyte is captured on bead surfaces (C), and matrix components are washed away. Next, a solution of a suitable chromogenic reagent (D) is injected, and when the reagent zone reaches the packed bead layer, the analyte reacts with reagent forming a species detectable by spectroscopy (E). Finally, beads are discarded or regenerated