Application of an improved biuret method to the determination of total protein in urine and cerebrospinal fluid without concentration step by use of Hitachi 7170 auto-analyzer

A biuret automated colorimetric assay for total protein in urine and cerebrospinal fluids was established. The procedures were as follows. Acidify all urine sample before analysis. Add precipitant Na2WO4 to urine samples. After 10 min, centrifuge, decant the supernatant fluid. drain the inverted tubes on absorbent tissue, dissolve the precipitation with 0.1 mol/L NaOH, and finally adapt the reconstituted urine to the Hitachi 7170 analyzer. A cell-free cerebrospinal fluid sample produced by centrifugation can be inserted in an auto-analyzer for protein measurement directly. The program: mix 35 mul sample (CSF or reconstituted urine) and standard with 0.2 mol/L NaOH; incurable at 37 degreesC for 5 min, and real A1. Add concentrated biuret reagent, and 10 min later measure absorbance A2 at 546 nm vs. reagent blank. Secondary wavelength was 700 nm. The test results were calculated against a one-point standard. This biuret colorimetric method was relatively simple, fast, and accurate for the determination of protein in urine and cerebrospinal fluid, with a wide linearity extending from 0.125 g/L up to 6 g/L, had a good correlation with Benzethonium chloride turbidimetry technique, and was a practical routine method. (C) 2001 Wiley-Liss, Inc.