Sodium reacts exothermically with aluminum in the presence of an excess of potassium and fluoride ions to produce NaK2AlF6 (elpasolite). This reaction can be used to rapidly and easily determine the sodium content of milk by thermometric titration with a standard solution of Al3+ as titrant.
Thermometric titrations are conducted under conditions of constant titrant addition rate. As the reaction that takes place is exothermic, the temperature rises, and the point at which the temperature curve bends marks the endpoint.
In addition to this Application Bulletin, you can find more information on thermometric sodium determination in foods in our application video: