Spectrophotometric Method for the Determination of Proteins with Water-Soluble Aniline Blue

In pH 1.0～2.3 acidic medium, water-soluble aniline blue reacts rapidly with proteins to form complexes, which causes the change of absorption spectra, the decrease of absorbance near 558 nm and the increase of absorbance near 634 nm. All △A(=A-A_0) values are proportional to the concentration of proteins. Beer's law is obeyed in the range 0～50 mg/L or 20～80 mg/L for the different proteins. Their molar absorptivities of fading reactions are between 1.72×10~5 and 1.99×10~6 L·mol~(-1)·cm~(-1). Based on these, we developed a new spectrophotometric method for the determination of proteins. The method is simple, rapid, repeatable and selective, and has been used for the determination of total amounts of proteins in human serum and urine samples with satisfactory results.