Direct Potentiometric Determination of Potassium and Sodium in Blood, Plasma, and Serum

A potentiometric analyzer, developed to directly measure potassium and sodium concentrations, was evaluated on aqueous solutions, whole blood, serum, and plasma. The analyzer consists of three electrodes—sodium, potassium, and reference—mounted in a flow-cell configuration, and a modified digital pH meter, which displays the ion concentrations directly. Volume of the cell is about 100 µl. The electrodes equilibrate to each new sample in less than a minute. Calibrated with aqueous standard solution, the system yields essentially the same values for whole blood and the corresponding plasma, and results agree with those obtained for the same samples of plasma by flame photometry.

Optimum Conditions for the Reaction Between Uric and Phosphotungstic Acids in the Presence of Glycerol-Silicate Reagent, Including a Proposed Modification of the Archibald Method

By controlling the alkalinity and the amount of phosphotungstic acid (PTA), turbidity and gelling in the final colored solution obtained in the reaction between uric acid and PTA in the presence of sodium glycerol silicate (NaGS) can be eliminated without using antiturbidity reagents. The optimum range of alkalinity is 0.55-0.76 mEq. of excess alkali in a total volume of 7.75 ml. A modification of the Archibald (1) method is proposed to assure optimum color development between uric acid and PTA-whether the uric acid is in an acidic protein-free filtrate or in a practically neutral aqueous standard solution.