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4. Conditioning a New Capillary

A new capillary must be conditioned prior to first use. Conditioning charges the exposed silanol groups on the inner walls of the bare fused-silica and allows for a proper electroosmotic flow. To condition a new capillary, it needs to be flushed with 1N NaOH for at least 2 hours at 20 psi. An alternative flush is 0.1N NaOH overnight. After completing the flush procedure, both ends of the capillary should be stored in deionized water until the next use.

  1. Place a vial filled with 3.5 ml of filtered 1N NaOH at the injection end of the capillary by screwing the vial into the plastic holder located inside the anode reservoir box. Place a waste vial filled with 3.25mL of deionized water on the lab jack beneath the flow cell of the UV-vis absorbance detector.
  2. Adjust the height of the lab jack so that the anode and waste vial lids are level. Make sure the ends of the capillary are equally immersed in the anode and cathode vials.
  3. Open the main valve on the top of the gas cylinder. Adjust the system pressure by tightening the control valve on the regulator, while monitoring the pressure (psi) on the pressure gauge connected to the regulator by copper pressure tubing. The pressure should be set to 20 psi.

    Pressure Regulator

  4. Pressurize the capillary by turning the black control switch on the three-way valve towards the gas cylinder. At this point remove the capillary at the cathodic end. A drop of liquid should be visible at the tip of the capillary. Visualizing this drop is useful in ensuring the capillary isn’t clogged. Open the interlock box and listen for air leaks. If the septum is leaking air, it will need to be replaced.

    Three-Way Valve

  5. Time the length of the flush with a stopwatch. After the flush is complete, turn off the pressure to the system by rotating the black control switch back towards the solenoid.
  6. Replace the anodic reservoir vial with a vial containing 3.5mL deionized water. Flush the capillary with one volume of deionized water (~60 seconds at 20psi) to remove excess base. Let both ends of the capillary stand in deionized water until next use.