Method for Electrometric Titration of Organic Acids of the Blood.

Abstract

Repeated attempts were made to apply Van Slyke and Palmer's 1 titrimetric method for the estimation of the organic acids of the blood plasma. These attempts were unsuccessful chiefly because with the small concentrations involved, no satisfactory end-point in the acid range could be obtained with the available indicators (thymol blue, bromphenol blue, Tropaeolin 00). In order to overcome this difficulty and also in the hope of gaining some information concerning the nature of the organic acids from the titration curves, the following method for the electrometric titration of these acids in the blood was developed.

The proteins are removed by means of ultrafiltration through collodion membranes or by precipitation with metaphosphoric acid; the carbonates, phosphates, oxalates and sugar are removed by addition of CuSO₄ and solid Ca(OH)_2. The filtrate may at this point be evaporated on the water bath to a small volume. More calcium hydroxide, sulfate and carbonate as well as basic cupric carbonate usually crystallize out on evaporation. The contents of the evaporating dish are passed through a small filter with suction washing the precipitate with several small portions of water until the volume of filtrate corresponds to 1.5 to 2 times that of the sample of plasma in the filtrate taken for evaporation. An aliquot corresponding to (3 to 5 cc. of plasma) of the alkaline filtrate is then placed in a simple electrode vessel containing a drop of methyl orange solution, and N HCl is added to a definite acid reaction. A small amount of quinhydrone is then added, the vessel is shaken and placed in a small water bath at 20° and is connected by means of a saturated KC1-agar bridge with a saturated calomel electrode suspended in the same water bath.