The Colorimetric Determination of the Serum Proteins

In connection with the study of the state of the calcium of the blood, we desired a rapid method for determining serum proteins. Wu (1) and Wu and Ling (2) have published a method for the determination of plasma proteins based on the color developed with Folin’s phenol reagent. The method as described by these authors is not very satisfactory due to the formation of turbid precipitates and the slow development of the color. Very recently Folin and Ciocalteau (3) have improved the phenol reagent by the addition of lithium sulfate. This permits the use of greater amounts of phenol reagent and sodium hydroxide without any resulting turbidity. By using more of the reagent the color development takes place far more rapidly and the amount of color is markedly increased. In connection with this improvement in the phenol reagent it seemed to us that a simplification could be obtained in the determination of serum proteins by adopting essentially Howe’s method (4) of salting out the globulin with sodium sulfate solution. The sodium sulfate was found to have almost no effect on the color developed so the albumin can be determined directly on an aliquot of the filtrate. We were able in this way to work out a satisfactory method for the analysis of the albumin and globulin, making use of 0.5 cc. of serum. Reagents.-The reagents required are 22.5 per cent sodium sulfate solution prepared from the anhydrous salt, 5 N sodium hydroxide, a standard tyrosine solution containing 200 mg. of pure dry tyrosine in 1 liter of approximately 0.1 N hydrochloric acid, and Folin’s phenol reagent. To keep all the sodium sulfate in solution, it is necessary to keep this reagent in an incubator.