The integrated modular and interchangeable unit of the present invention comprises an analyte concentrator-microreactor (ACM) device having four entrance-exit ports identified as connection areas to a transport capillary for sample and buffer introduction, and to a separation capillary of a cartridge-cassette filled with an appropriate separation fluid for optimal separation of the analytes of interest. Affinity ligand groups are immobilized to microstructures contained within the main inner cavity or channel of the device or directly to the wall of the main inner channel for capturing one or more analytes. The inlet and outlet ends of the transport capillary are connected through a parallel design option to the analyte concentrator-microreactor (ACM) device to facilitate the path of sample and buffers through the inner cavity or channel of the analyte concentrator-microreactor (ACM) device.