A Study of the Estimation of Sodium in Blood Serum

Without doubt the most satisfactory procedure for the quantitative determination of small amounts of sodium is that involving its precipitation as uranyl zinc sodium acetate, (UO&ZnNa(CH,C00)9.6Hz0, first introduced by Barber and Kolthoff (2). Applications of this method to biological material have been numerous, since the triple salt is readily estimated by a variet,y of gravimetric, calorimetric, or volumetric procedures. Of these procedures that which appears to offer the greatest accuracy with the greatest sensitivity is the volumetric one employed by Kolthoff and Lingane (8). This, in brief, involves the reduction of hexavalent uranium in the triple salt to UxV and some U”‘; the latter is easily oxidized by air at room temperature to the quadrivalent state which is less susceptible to air oxidation. The quadrivalent uranium is then oxidized quantitatively to the hexavalent state with dichromate. The application of this volumetric procedure to biological materials has not received the attention that the method merits. We therefore present, in the following pages, a method for the determination of sodium in blood serum based on these principles. Accurate results are obtainable on 0.2 ml. samples of serum. In proof we present parallel determinations on 10 to 20 ml. samples by the classical chloroplatinate method. For comparison we also present results obtained by the gravimetric method for estimating the uranium triple salt as described by Butler and Tuthill (3) and the older pyroantimonate method of Kramer and Gittleman (9). A comparison is also made of the values obtained on trichloroacetic acid filtrates of serum and ashed samples.