A modification of Folin's uric acid method

Abstract

In an effort to improve Folin's uric acid reagent it was found that by dialyzing under special conditions Folin's solution and evaporating the solution so dialyzed a superior reagent was obtained. A similar, though not identical, reagent was prepared by boiling down Folin's solution and filtering off the precipitate. When mixed in the proper proportions these two substances yield a reagent superior to Folin's in the following respects.

1. There is no precipitate such as is frequently encountered with Folin's solution.

2. The color developed with a given quantity of uric acid is about four and a half times as intense as that developed in Folin's method.

3. The color does not fade over a period of many hours.

Since this work was done we have learned of Wu's isolation of the pure ammonium phospho-18-tungstate. 1 This substance was prepared by his inethod and its chromogenic powers were found to be the same as those of our salt. Like the latter the pure ammonium salt gives a better color in the absence Na₂CO₃ and sulphite lessens the color markedly, facts which explain why Wu apparently did not recognize that his salt under proper conditions gave more color than Folin's original solution. Our method is simpler and yields more usable material than Wu's method would if used for the same purpose.

The actual method of blood analysis is somewhat modified. No sodium carbonate is used, the cyanide furnishing the requisite alkalinity. Benedict's standard must be used. The cyanide must be measured to an accuracy of o.I c.c.