Analysis of Sodium in Foodstuffs by Thermometric Titration

By

Consumers and regulatory agencies are expressing more and more interest in the true amount of sodium contained in food products. Sodium has traditionally been indirectly tested using a silver nitrate precipitation reaction:

The amount of sodium would be calculated by assuming a 1:1 molar ration of chloride ions to sodium ions in the food. This assumption is not necessarily the case when common sodium containing food ingredients such as sodium benzoate, mono-sodium glutamate or chloride containing ingredients such as potassium chloride are present in the food matrix as well as sodium ions that may be present in the food itself. Common methods of testing the true amount of sodium directly have typically been atomic absorption spectroscopy or inductively coupled plasma spectroscopy. Although specific to sodium for analysis, these techniques typically involve significant capital investments in equipment and infrastructure, costly ultra-pure reagents and lengthy sample preparation and system calibration. Metrohm USA is excited to announce a method of direct thermometric titration of sodium in food stuffs that is specific, rapid, robust and economical. Thermometric titration is a form of titration using the heat of enthalpy of entropy produced by a chemical reaction to determine the endpoint. This method of titration is free from the electrochemical and solvent effects that are present in many types of titration making them difficult to adapt to some food matrices. To determine the amount of sodium the food is first masticated or homogenized to make a homogeneous mixture. The prepared mixtures is then titrated with a standardized solution of aluminum containing a stoichiometric excess of potassium ions in the presence of ammonium hydrogen difluoride at ~pH3 to give an exothermic reaction, forming insoluble NaK2AlF6.

The titrant is standardized against a solution prepared from anhydrous sodium sulfate.

Equipment Required:
Metrohm 859 Titrotherm Sodium Analysis Kit with PC

Reagents Required (included with kit):
Titrant: Mixed 0.5mol/L Al(NO3)3, 1.1mol/L KNO3 solution.
Complexation reagent: 300g/L NH4F.HF
Waste neutralization solution: Boric acid solution

Conclusion

  • These data show that the thermometric analysis of sodium is a robust, precise and accurate test method.
  • Enables a QC lab to analyze sodium quickly and accurately.
  • Current sample preparation techniques for chloride titrations may be kept for ease of integration into existing methodology.
  • Robustness of maintenance free probe allows for simplified sample prep if desired.
  • Simple to use software that is readily integrated into existing LIMS and other software systems.
  • Very rapid analysis.
  • Uses all off the shelf components. No parts are customized for this analysis.

Published In

Laboratory Etiquette Magazine Issue Cover
Laboratory Etiquette

Published: May 9, 2011

Cover Story

Laboratory Etiquette

Many lab managers still remember them from their student days—a handful of hastily stapled printouts sternly titled “Laboratory etiquette—Acceptable standards of conduct.” Those were rules to live by, and the smallest violation landed a budding laboratory scientist in front of the ticked-off chief instructor.