Titer Determination of NaF and Blank Value by Thermometric Titration
Fully automated rapid and accurate analysis using Aluminum nitrate nonahydrate
The application note describes the thermometric titer determination of Sodium fluoride and the Blank value using Aluminum nitrate nonahydrate as primary standard. A linear regression over 4 different samples enables a simultaneous determination of blank and titer.
Background:
Thermometric titration is a technique in which endpoints can be determined accurately and precisely; by measuring the temperature changes observed as a consequence of the heat liberated by the reaction between the analyte and the reactant.
Thermometric titrimetry is widely used in determination of analytes that undergo exothermic reaction to form precipitates. Aqueous Fluoride, Aluminum, Potassium and Sodium ions form Elpasolith (NaK2AlF6) in acidic conditions. The reaction is strongly exothermic. Therefore, it can be used to determine these four ions by thermometric titration. In the presence of Potassium and Sodium, it is possible to determine the content of aluminum using sodium fluoride as titrant. Similarly, if Aluminum ions are used as titrant, Fluoride content can be determined.
Reaction:
Al3+ + Na+ + 2K+ + 6F- --------> NaK2AlF6 ↓
The thermometric determination of the blank value and titer of sodium fluoride using Aluminum nitrate nonahydrate as primary standard is given in the application.
Sample solutions of various concentrations containing Aluminum ions are prepared using standard aluminum nitrate. A buffer solution of pH 4.5 is prepared with acetate or chlorides of potassium and sodium ions. This reaction mixture when titrated with sodium fluoride undergoes the exothermic reaction forming precipitate of Elpasolith salt.
Thermometric titration follows course of enthalpy change by measuring the temperature. In this reaction, the temperature rise corresponds to the exothermic formation of the aluminum complex with sodium, potassium and fluoride.
Related Applications:
