Within the scope of the USP monograph modernization, sodium is determined in potassium sodium tartrate applying cation chromatography with direct conductivity detection. The USP41 monograph for «Potassium sodium tartrate» does not yet mention an assay for sodium. The separation is performed on a Metrosep C 6 - 150/4.0 column (L76). The assay of potassium is performed with two commercially available products according to USP definitions. All acceptance criteria are fulfilled. See AN-C-182 for the respective determination of potassium. Apllying this method allows to determine sodium and potassium simultaneously according to USP.