A Micromethod for the Determination of Sodium*

In view of the increasing importance of acid-base equilibrium and of the r81e of the inorganic elements in the body economy, the accurate determination of sodium in the blood and body fluids becomes of increasing importance. Barber and Kolthoff (1) in 1928 were the first to employ the triple salt, uranyl zinc sodium acetate, for the quantitative determination of sodium. They ascribed to t,his salt the composition (UO&ZnNa(CH&00)9. 6Hz0, the amount of sodium in a weighed precipitate of this salt being 0.01495 the weight of the precipitate. Butler and Tuthill (2) applied the gravimetric procedure of Barber and Kolthoff for the determination of sodium in biological material. For urine, they first precipitated the phosphate (which interferes with the gravimetric method by precipitating as insoluble uranyl phosphate) with calcium hydroxide, and they precipitated the protein with solid mercuric chloride. In their determination of sodium in blood serum they used 1 cc., digesting it first as in a micro-Kjeldahl method before proceeding with the gravimetric determination. These gravimetric methods give fairly good results, but the methods are tedious and require relatively large amounts of material. Salit (3) describes a modified procedure for the gravimetric determination of sodium in urine and feces, and a modified colorimetric method for whole blood or serum, in which but 0.5 cc. of serum is required or 0.2 cc. of whole blood. Salit’s modification