A spectrophotometric method for determination of total proteins in cow milk powder samples using the o-nitrophenylfluorone/Mo(VI) complex

A new spectrophotometric method has been developed for the determination of protein in Tween 20 microemulsion medium. The method is based on the interaction between protein and o-nitrophenylfluorone–Mo(VI) complex as a spectral probe. Under the optimal conditions, Beer's Law is obeyed over the range of 0–16 μg mL−1 bovine serum albumin (BSA) with the detection limit being 15 ng mL−1. Both the influence of reaction variables and the interference of coexisting substance are studied. The proposed method has been applied to the whole milk powder samples with satisfactory results. The recoveries are between 97.6% and 105.8%, and the standard relative deviations are less than 4.3%. Molar ratio and slope ratio methods are used to determine the binding number of BSA with the complex and the value 96.