Determination of Small Amounts of Potassium

Abstract

THE volumetric determination of the cobaltinitrite complex appears to have been neglected as a rapid, accurate, and precise method for the estimation of small amounts of potassium. The best known is that of Kramer and Tisdall (6) who precipitated the dipotassium sodium cobaltinitrite, decomposed it with alkali, oxidized the liberated nitrite with permanganate, and back-titrated with standard sodium oxalate. The disadvantages of this method were pointed out by Brown, Robinson, and Browning (#) who used ceric sulfate instead of permanganate.Recently, Weichselbaum, Somogyi, and Rusk ( 8) have given the experimental conditions for the preparation of the potassium silver cobaltinitrite first announced by Burgess and Kamm (S). Their method gave a precipitate of constant composition between certain carefully defined limits. Potassium was then calculated either by determining the nitrite content gasometrically, according to Kramer and Gittleman (5), or by a Volhard titration of the silver present.More recently, Kaye (4) presented a method whereby the nitrite content of the sodium potassium cobaltinitrite is oxidized with excess ceric sulfate and back-titrated iodometrically.The method presented here was used -with success in the mineral analysis of bile and other biological materials, the results of which will appear elsewhere shortly. Potassium silver cobaltinitrite, K2AgCo(N02)e, was precipitated, the nitrite liberated with hot alkali, acidified, and immediately titrated with ceric sulfate directly, using ferroin.The procedure is satisfactory for the determination of potassium in amounts ranging from 0.1 to 0.2 mg. The error does not exceed 2 per cent. This method lends itself especially to the rapid analysis of biological materials. ReagentsSodium cobaltinitrite, 12.5 per cent solution of the pure dry salt, freshly prepared. Mallinckrodt analytical reagent was found suitable.Silver nitrate, approximately 0.2 M. Ceric sulfate, 0.01 N, prepared by diluting stock 0.1 N, standardized against sodium oxalate. This solution is remarkably stable, changing less than 0.1 per cent per month.Sodium hydroxide, approximately 1 2V. Sulfuric acid, approximately 1 A7. Ferroin, o-phenanthroline ferrous complex, solution obtained from the G. F. Smith Chemical Co., Columbus, Ohio.

Determination of Nitrogen, Phosphorus, and Potassium in Leaf Tissue. Application of Micromethods

“…This causes turbidity which is compared visually or photometrically with standards similarly treated (6). For more precise work and usually for semimicroquantities, the potassium cobaltinitrite precipitate is separated by filtration or centrifugation and then can be measured colorimetrically by its reaction with a colored oxidizing agent (34) or by titration with an oxidizing agent (14) or with nitroso R salt (25). Klein and Jacobi ( 14) have described a procedure for determining 0.1 to 0.2 mg. of potassium by a titration of silver potassium cobaltinitrite.…”

Ceric Salts in Volumetric Analysis

“…Potassium has been precipitated as potassium silver cobaltinitrite. The nitrite was then liberated with hot alkali, the solution acidified and titrated with ceric sulfate, with ferroin as indicator (71). A comparative study has been made of permanganate and ceric sulfate for the oxidation of cobaltinitrite in the estimation of potassium in its chloride solution and in soil extracts (55).…”