Cleaning of the Diaphragm (fritted) Generator

This procedure is for deep cleaning of the generator when the frit has become plugged up in some fashion.

REAGENT AND EQUIPMENT:

ALCOHOLS  Methanol or ethanol, reagent grade, should contain a low amount of water. Alcohols are used to rinse the frit after nitric acid cleaning and water rinsing.

OTHER SOLVENTS  A wide variety may be used to remove sample build-up on the frit. Oils can best be removed with petroleum solvents – xylenes, toluene, chloroform, methylene chloride, etc. With other samples, the analyst is usually aware of solvents in which their samples are soluble. Use these solvents to remove any build-up on the frit. Rinse the frit with water to remove the solvents before cleaning with nitric acid. Although water will not remove all of the solvents, it is not good practice to add nitric acid to an organic solvent, so therefore, use the water rinse. The frit material, the platinum anode, and cathode are relatively inert in most solvents and acids; however, strong alkalis should be avoided for they may damage the frit.

NITRIC ACID  Reagent grade is suggested. Technical grades can be used if reagent grade is not available. Nitric acid is preferred to other acids. Nitric acid is obtained from any chemical supply house. The cleaning procedure requires about a 75% aqueous solution. Make this by placing 25 cm3 (mL) of water in a container and adding 75 cm3 (mL) of concentrated acid to the container. The quantities do not have to be exact, but try to have a mixture with one part water to three (3) parts nitric acid. Handle and dispose of solutions in an approved manner.

CONTAINERS:

Any acid and solvent resistant glassware or plastic ware may be used.

PROCEDURE

1. Remove the cathode solution cell from the titration vessel and dispose of the catholyte (generator) solution.

2. Rinse cell with Methanol or Isopropanol.  Add solvent to generator up to small breathing hole in side and place in beaker and let solvent drain through frit for 10 minutes.  Discard remaining solution.

3. Rinse the cell with water.  Add water to generator up to small breathing hole in side and place in beaker and let water drain through frit for 10 minutes. Discard remaining solution.

4. Place the cell in a small beaker and fill to breathing hole with of 75% nitric acid in water. Concentration is not critical.  Let drain through frit for 15 minutes. Discard remaining solution.

5. Rinse the cell with water.  Add water to generator up to small breathing hole in side and place in beaker and let water drain through frit for 10 minutes. Discard remaining solution.

6. Rinse cell with Methanol or Isopropanol.  Add solvent to generator up to small breathing hole in side and place in beaker and let solvent drain through frit for 10 minutes. Discard remaining solution.

7. Dry overnight or in a 60 degree C oven for at least 4 hours.

8. At this point, place the cathode solution cell in the vessel and add the generator solution. The titration vessel is now ready for use.

* NOTE: Also known as the generator cell.

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