Voltammetric albumin quantification based on its interaction with carminic acid

In a weak acidic Britton-Robinson (B-R) buffer of pH 4.0, human serum albumin (HSA) can react rapidly with carminic acid (CAA) to form a supramolecular complex. Microelectrostatic fields in the molecular structure of HSA cause the electrostatic binding reaction of the positively charged CAA with the negatively charged HSA. CAAhas a sensitive, second order derivative linear sweep voltammetric reductive peak at - 0.54 V (vs. SCE) on a dropping mercury electrode (DME). After the addition of HSA to a CAA solution, the reductive peak current of CAA decreased without a shift of the peak potential. Based on the decrease of the peak current, a sensitive voltammetric method for the determination of microamounts of the protein is proposed. The conditions for the binding reaction and the voltammetric detection were optimized. Under the optimal conditions, the decrease of the voltammetric detection were optimized. Under the optimal conditions, the decrease of the voltammetric peak current was in proportion to the quantity of USA in the range of 2.0 to 70.0 mg l -1 , with a linear regression equation Δ/ p" (nA) = 11.74 C (mgl -1 ) 12.33 and a detection limit of 2.0 mg l -1 (3σ). The method was further applied to the detection of different kinds of proteins, such as bovine serum albumin (BSA), oval albunim (OVA), lipase, etc. The established method was further applied to the determination of the albumin content in human serum samples and the results obtained by this method were in good agreement with the traditional Coomassie Brilliant Blue G-250 (CBB G-250) spectrophotometric method. The binding mechanism is discussed and the binding ratio was calculated from the voltammetric data.