A Volumetric Method for Determination of Potassium in Biological Materials

During the past 3 years we have carried out analyses of tissues for potassium in this laboratory using the separation by chloroplatinic acid. For 1 year potassium has been estimated by a Volhard titration of the chlorine in KzPtC16 separated by the usual procedure. Because the method seems more accurate and convenient than previous titrimetric methods, a description is warranted. SolulionsSolution of chloroplatinic acid in 1 N HCl. 26.5 gm. of chloroplat,inic acid (HzPtCL.6HzO) dissolved in 100 ml. of 1 N HCl. Acid 80 per cent ethyl alcohol saturated with KzPtCls. Add a small amount of KzPtCl6 to 15 ml. of approximately 1 N HN03. Shake for a few minutes until no more K2PtCl, dissolves. Add 80 ml. of stock 95 per cent alcohol. Filter just before using. 15 per cent solution of NaHS03. 0.05 N AgNOa in concentrated HN03. 0.02 N NH,SCN. Ground ferric alum. Procedure Most biological material will require a preliminary removal of phosphate from the ash. To a suitable amount of ash which is dissolved in water or dilute HCI add sufficient chloroplatinic acid to combine with all the K and Na. Evaporate until the salts separate out but still look moist on cooling. Add a small amount of 80 per cent acid alcohol and filter,’ using preferably an automatic