A Method for the Preparation of Blood Filtrates for Analysis.

Abstract

The use of zinc salts for the precipitation of blood proteins furnishes a method of preparing filtrates in which fermentable sugar (glucose) is the only substance to reduce alkaline copper solutions. The reducing substances other than sugar—responsible for the “residual reduction” of fermented blood filtrates—are precipitated along with the proteins so that sugar determinations in zinc filtrates give true blood sugar values.

In a simple method of deproteinization we employ the following 2 reagents:

Reagent I. 12.5 g. of zinc sulphate (ZnSo₄7H₂O) are dissolved in water, 125 cc. of 0.25 normal sulfuric acid are added, and made up with water to one liter.

Reagent II is a 0.75 normal solution of sodium hydroxide.

The 2 reagents have to be in such a definite relation that when Reagent I is titrated against Reagent II in the presence of phenol phtalein, 25 cc. of I should require 3.35 to 3.40 of II to produce a permanent pink color.

Procedure: In order to prepare a 1:10 filtrate, lake one volume of blood in 8 volumes of Reagent I, add one volume of Reagent II, stopper tightly, shake well, filter after a few minutes through a dry filter paper. Centrifuge before filtration if a maximum yield of filtrate is wanted.

For the preparation of filtrates of concentrations other than 1:10, we use a somewhat different technique and pair of reagents. Reagent A is a 19.5% zinc sulphate solution, Reagent B a normal sodium hydroxide. One volume of blood requires one half a volume of each of these reagents for deproteinization. If, for instance, a 1:5 filtrate is desired, lake one volume of blood in 3 volumes of water, introduce one half a volume of Reagent A, mix, then add one half a volume of Reagent B, stopper tightly, shake well, filter after a few minutes.