Collaborative study of the determination of sodium in dietetic foods by the sodium ion electrode method.

The dietetic food sample is diluted with total ionic strength adjusted buffer. The electrode potential of the sample is measured, known increments of sodium are added, and the electrode potential is measured after each addition. The mv readings obtained are plotted on Gran's paper and the concentration of sodium in the sample is found from the intercept of the extrapolated straight line. Seven processed dietetic vegetables and 2 spiked samples were sent to 7 collaborators. There was a 95.8% agreement between the results from the 7 collaborators and the Associate Referee for the unfortified samples. Recoveries of 98.5 and 95.1% were obtained on fortified samples, based on results from 5 collaborators. The statistical analysis indicates minimal bias and adequate precision for determination of sodium in dietetic food at the current regulatory requirements. The method has been adopted as official first action.