A commonly used method for quantifying sodium in foodstuffs is to determine the counterion chloride using argentometric titration, the concentration of which can be used to deduce the sodium concentration from the 1:1 stoichiometry of sodium chloride. This method involves errors because sodium is not only present with chloride as the counterion. A new method for direct titration of sodium with thermometric endpoint detection solves this problem.
Thermometric titration shares with potentiometric titration the use of a sensor to detect the endpoint of the titration reaction. In the case of thermometric titration, however, the sensor is a fast responding thermometer. Hence, instead of measuring the electrochemical potential in the solution, this robust, highly sensitive thermometer tracks the reaction enthalpy, ie the temperature change in the solution.
The endpoint of the titration is marked precisely by the moment, when the reaction stops and no significant temperature change is registered any longer in the solution. Because it relies merely on a change of solution temperature to find the endpoint, there is no need to calibrate the sensor. Sensor maintenance is minimal, and it can be stored dry between titrations.
As for sample preparation, users only need to ensure that the matrix does not prevent the analyte from reacting with the titrant and that the sample is sufficiently mobile. Accurate results are available in less than two minutes.
Metrohm provides the 859 Titrotherm with tiamo software for thermometric titrations, a total solution that can easily be automated by integrating an autosampler.