Determination of Albumin and Globulin in Urine.

Abstract

Albumin and globulin are separated by precipitating the latter with sodium sulfate, as in Howe's 1 technique for plasma protein separation. The separated proteins are determined by the colorimetric method of Autenrieth, 2 which can be made practical for general colorimetry by introducing pure biuret as a standard. One mg. of biuret gives a color equal to that of 0.924 mg. of urinary proteins treated with alkali and copper sulfate, as described by Autenrieth. 2

The standard solution is made by dissolving 0.4 gm. of biuret in water and diluting to 150 cc. Five cc, containing 13.33 mg. of biuret, is colorimetrically equivalent to 12.3 mg. of urinary proteins.

For total protein, enough urine to contain 8 to 20 mg. is precipitated with an equal volume of 10 per cent trichloroacetic acid. The precipitate is redissolved in 3 per cent NaOH, treated at 10 cc. volume with 0.25 cc. of 20 per cent CuSO₄ · 5H₂O, and compared with 1 cc. of the biuret standard similarly treated.

Globulins are precipitated by treating the urine at 38° with an equal volume of 44 per cent Na₂SO₄. In the filtrate, the albumin is precipitated with trichloroacetic acid, and determined as described for total proteins. Globulins are calculated as (total protein)—(albumin).