56 . the Micro - Determination of Potassium

THE determination of potassium is more troublesome than that of any other biologically important cation; at the same time there are many conditions involving variations in the electrolyte content ofthe body fluids in which accurate estimations of potassium are desirable. It therefore appeared worth while to try to devise an analytical method for potassium which should be simpler than those at present in use; this paper describes a new method which offers certain advantages of simplicity whilst giving a degree of accuracy not significantly less than those claimed for the more time-consuming procedures. The methods at present available for the determination of potassium fall into two groups: (1) determination as the chloroplatinate and (2) determination by one of the various modifications of the cobaltinitrite procedure [compare Peters & Van Slyke, 1932]. The chloroplatinate method is excellent for inorganic analysis when reasonably large quantities of material are available; it loses accuracy however when adapted to micro-analysis. The cobaltinitrite methods which have been most widely employed in biological work suffer from the theoretical disadvantage that there is uncertainty in the composition of the final precipitate; this means that although a series of analyses conducted by one worker under constant conditions may give mutually consistent results with a small margin of error, the basis of the method is not satisfactory. In the search for a new procedure attention was directed to the possible use of dipicrylamine; this compound, di(2:4:6-trinitrophenyl)amine, forms a deep