Co-precipitation to form HA

The method The Cardiff Catalysis Institute will use to form HA in the lab is called co-precipitation.

To do this you mix two soluble (dissolved) compounds together and under the right conditions, they react to form a solid crystal (precipitate).

In our case, they will take a calcium containing solution (liquid), and a phosphate containing solution (liquid) and mix them together in a warm flask. An alkaline pH (greater than 7) helps the reaction to occur, so they will also add a 3rd ingredient to maintain this pH in the flask.

To mimic the conditions in a nappy wash, they can adjust the relative concentrations of phosphate and calcium to mimic:

  • Hard/soft water (main focus as this was a winning hypothesis in our vote)
  • Phosphate in detergent.
  • Drinking water that has had phosphate added
  • Calcium / phosphate levels in baby urine

In a little more detail for those of you who are chemistry minded – they will use soluble calcium nitrate or calcium chloride and mix it with potassium hydrogen phosphate or phosphoric acid and add ammonium hydroxide as a base to maintain an alkaline pH.

Their method is based on this paper: