The bead suspension is aspirated via port # 6 into the holding coil by flow reversal. After the valve is switched to port #2 (shown), the beads are packed into the flow cell, and retained by a hollow plug (A) or optical fiber (B). While flow cell A is suitable for BI spectroscopy, flow cell B is used for monitoring of eluted species, as in BI renewable column chromatography. Bead transport is carried out at moderate flow rates (50μL/sec), in order to transfer all beads within the selected volume of suspension through the flow channel and to pack them reproducibly into the flow cell. It was found that slower flow rates do not provide well packed beads. Bead perfusion by sample solution is carried at slow flow rates (typically at 1 μL to 5 μL/sec). Bead discharge takes place as needed or at the end of each measurement cycle. The Sephadex or Sepharose 4B beads can be forced through and around the plug using fast flow rates (200μL/sec), but this approach is not recommended, especially for B configured flow cells, since the long column of elastic beads may become compressed, plugging the conduit. The resulting backpressure might damage the pump. Instead, a small volume (100μL) at high flow rate reversal (200 μL/sec) is used to aspirate beads into the holding coil and then expelled to waste after the valve switch.