A Microcolorimetric Method for the Determination of Potassium in Biological Materials

Several methods for the determination of potassium in biological materials have been described.According to the principal chemical reactions the most widely used methods may be classified into three groups, methods based on (1) the sodium cobaltinitrite reagent, (2) the silver cobaltinitrite reagent, and (3) the chloroplatinic acid reagent.Certain drawbacks in the first two methods lie in the fact that both the potassium sodium cobaltinitrite and the silver potassium cobaltinitrite compounds are said to be rather doubtful in composition (l-6).The ratio of sodium or silver to potassium is believed to vary according to their relative concentrations in the sample and reagent, the temperature and rate at which the precipitation takes place, and the temperature at which the precipitate is dried.The interfering substances are iron, aluminum, manganese, barium, calcium, magnesium, and copper (7).In principle, the chloroplatinate methods are by far superior to those based on the sodium or silver cobaltinitrite compound, because KzPtClG has always a definite composition (8)(9)(10)(11).Also, in this method, the number of interfering substances is smaller.Ammonium, alcohol, iron, copper, and ferrocyanide are said to interfere (9, 10).But since ashing is always employed with this method, ammonium and alcohol are destroyed, and iron and copper are converted into insoluble oxides in the process.However, the hitherto employed methods of ashing biological materials for potassium determinations are rather complicated.Shohl and Bennett (10) and many others have found loss in potassium by the usual dry ashing procedure.Shohl and Bennett, therefore, first digest the sample with sulfuric acid, and then transfer it to a