A New Micromethod for Determination of Protein in Cerebrospinal Fluid and Urine

Abstract We developed a new micro-scale procedure for determination of protein in cerebrospinal fluid and urine. The sample (50 µl) is mixed with a trichloroacetic acid—Ponceau S dye solution. The proteins, together with a proportional amount of dye, are precipitated and the red precipitate is dissolved in dilute sodium hydroxide solution, giving a violet-colored solution. This color, linearly proportional to the amount of protein present (up to 150 mg/dl), is measured spectrophotometrically at 560 nm. By varying the sample size alone, protein concentrations up to 1500 mg/dl can be measured. The detection limit for the method is 2 mg/dl of sample. Precipitation of the proteins is independent of temperature and albuminbinding compounds, and is not appreciably affected by the albumin—gamma globulin ratio.