Determination of total sodium in commercial cheeses by thermometric titration

Samples of shredded, grated, or sliced cheese are dispersed with a high-speed disintegrator in a solution of trichloroacetic acid, which denatures protein and assists in the liberation of all sodium from the matrix. Toluene is added in a second step of the dispersion process to assist in the solubilization of fat. Ammonium fluoride solution is then added, and the sodium titrated with a titrant comprising 0.5 mol/L Al(NO₃)₃ and 1.1 mol/L KNO₃ to an exothermic endpoint.

Na⁺ + 2K⁺ + Al³⁺ + 6F^- ↔ NaK₂AlF₆ ↓

In this determination, ammonium fluoride (NH₄F) has been found to give sharper endpoints than ammonium bifluoride (NH₄F ∙HF). In addition to this application note, you can find more information on thermometric sodium determination in foods in our application video available on YouTube: https://youtu.be/lnCp9jBxoEs

Download AN-H-112 (EN)