An absolute method for protein determination based on difference in absorbance at 235 and 280 nm

Because of the importance of quantitative determination of protein in the research laboratory as well as in the food and feed industries (1), search for the ideal method continues unabated after many years. Methods available include nitrogen determination (Kjeldahl (2) and Dumas (3)), hydrolysis of the protein, derivatization of the amino acids with phthalaldehyde and fluorescence determination (4), determination of bound or free lysine (5) or glutamate (4), and the Lowry (6), biuret (7) dye-binding (8–11) turbidity (12) and spectral methods (13). With the exception of the spectral methods, the methods involve destruction of the sample.In this paper we report the use of difference in absorbance between 235 and 280 nm for determination of protein concentration.