Electrochemical determination of heparin using methylene blue probe and study on competition of Ba2+ with methylene blue for binding heparin

Cyclic voltammetric investigation of the interaction of methylene blue (MB) with heparin (hep) at a gold electrode is presented. The combination of MB with heparin formed a nonelectroactive complex MB–hep, which resulted in the peak current decrease of MB. The anodic peak current difference of MB was found to be proportional to the concentration of heparin in the range of 0.666–64.5 μg mL−1 with a detection limit of 270 ng mL−1 and a satisfactory result was obtained for the determination of heparin in injection samples. The equilibrium constant for MB–hep complex was calculated to be 7.32 × 105. The dynamic process of competition of Ba2+ with methylene blue for binding heparin was monitored using quartz crystal microbalance (QCM) technique. The reaction rate constant between Ba2+ and MB–hep was estimated to be 0.0022 s−1.