Biochemistry. A simple spectroscopic method to determine the total protein concentration of a sample. The method is based on the binding of the dye Coomassie Brilliant Blue to proteins in an acid solution. As the protein concentration increases, the color of the test sample becomes darker. The absorbance maximum of Coomassie is shifted from 465 to 595 nm. The protein concentration of the sample is determined by comparison to a series of protein standards, (e.g., bovine serum albumin, BSA).