Table salt is just one form in which we absorb sodium in our diets. While essential to our health in small doses, sodium can have a negative impact if it is consumed in large quantities. Therefore, it is important that methods for accurately determining sodium levels in food are available.
The sodium content of food and beverages is usually determined indirectly through a precipitation reaction with silver nitrate. This approach assumes that the chloride ions are present in a molar ratio of 1:1 with the sodium ions, which is not always the case. On the other hand, established methods for the direct determination of sodium such as AAS or ICP/MS are very expensive.
Thermometric titration is a cost-effective and straightforward alternative. First, proteins in the sample are precipitated with trichloroacetic acid and then separated through filtration or centrifugation. An aliquot is titrated in the presence of NH4F at a pH value of 3 with an aluminum nitrate solution with an excess of potassium ions. The exothermic reaction produces insoluble NaK2AlF6.
