Voltammetric studies on the interaction of orange G with proteins. Analytical applications

The interaction of orange G with protein was investigated by voltammetric method in this paper. In pH 2.0 Britton-Robinson (B-R) buffer solution orange G displayed an irreversible voltammetric reduction peak at -0.17 V (vs. SCE) on mercury working electrode. The addition of human serum albumin (HSA) into the orange G solution resulted in the decrease of the reduction current peak apparently without the changes of peak potentials and no new peaks appeared. The electrochemical parameters of orange G solution in the absence and presence of HSA were calculated and compared. The results showed that there were no significant changes, which indicated that the electrochemical behaviors of reaction solution on the mercury working electrode showed no changes and a supramolecular electrochemical inactive biocomplex was formed. The interaction mechanism was due to the formation of the microelectrostatic field in albumin structure in aqueous solution and caused the interaction with orange G, which induced the decrease of the equilibrium concentration of orange G in the reaction solution, and the decrease of the reductive peak current. The interaction conditions were discussed carefully. Under the optimal conditions the decrease of peak current was proportional to the concentration of protein and further used to the determination of different kinds of proteins. The calibration curves for the determination of HSA, bovine serum albumin (BSA), ovalbumin (OVA), bovine hemoglobin (BHb), lipase were linear over the ranges of 4.0 similar to 28.0 mg L-1, 4.0 similar to 30.0 mg L-1, 2.0 similar to 20.0 mg L-1, 2.0 similar to 25.0 mg L-1, 2.0 similar to 30.0 mg L-1, respectively. The detection limit was 3.0 mg L-1 for HSA, 3.5 mg L-1 for BSA, 1.0 mg L-1 for OVA, BHb and lipase. The new established electrochemical method was applied to determine the content of albumin in healthy human serum samples and the results were in good agreement with the traditional Coomassie Brilliant Blue (GBB G-250) spectrophotometric method.