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Chemistry LibreTexts

5. Daily System Preparation

The Homebuilt CE system must be prepared for analysis each day. This involves turning on the UV-visible absorbance detector and flushing the capillary to restore the enviroment inside the bare fused-silica. The flushing protocol outlined below is best suited to the experiments outlined in Learning Modules I through IV.

  1. Turn on the UV-visible absorbance detector to allow sufficient warm up time. Set the wavelength on the UV-visible absorbance detector to the correct value. The wavelength should correspond to the maximum absorbance value of the analyte. The optimal detection wavelengths for most analytes can be found in the MERCK index or they may be determined experimentally.
  2. To flush the system, first open up the valves on the gas tank by turning the main valve and the secondary valve. The secondary valve on the front of the regulator is useful for fine control of the pressure.

    Pressure Regulator

  3. Adjust the pressure to the desired value for flushing (for example 20 psi). If the pressure is too high and does not seem to decrease, unscrew the anode vial to allow air pressure to stabilize (you will hear the air escaping from the vial) and then readjust the pressure using the front secondary valve.
  4. Flush the system. This is done by filling two 3 mL vials. The first vial will contain filtered 1N NaOH (see Solution Preparation for Details) and is placed at the anodic end of the capillary. The second vial contains deionized water and is placed at the cathodic end of the capillary.
  5. Turn on the pressure to the system by turning the black control switch. At this point remove the capillary at the cathodic end. A drop of liquid should be visible at the tip of the capillary (ensuring the capillary isn’t clogged).
  6. Allow 1N NaOH to run through the system for 20 minutes.
  7. Fill a new sample vial with 3.5 mL of deionized water. Replace the anodic vial with this new water vial. Turn the pressure back on and allow the water to run through the system for 10 minutes.
  8. After a 10 minute deionized water flush, turn off pressure, remove water vial and replace with vial of run buffer that has been filtered. Adjust the system pressure to 10 psi by using the black valve on the regulator. Flush with buffer for 20 minutes and turn pressure off.