The interaction of heparin (Hep) and methyl violet (MV) was studied by electrochemical methods. In pH 1.5 Britton-Robinson (B-R) buffer solution, methyl violet has an irreversible reduction peak at －0.58 V (vs. SCE) on mercury working electrode. After the addition of Hep into MV solution, the reduction peak currents decreased with the positively movement of the peak potentials. The electrochemical processes of the interaction between Hep and MV were studied and the results showed that an electro-active complex was formed with the changes of the electrochemical parameters. The binding constant and the binding ratio were calculated as 2.47×10¹⁴ and 1∶3, respectively. The conditions of the binding reaction and the electrochemical detection were optimized. Under the optimal conditions the decrease of the peak current was proportional to the concentration of Hep in the range of 0.20～4.00 mg/L with the linear regression equation as ∆I_p″ (nA)＝－724.9＋1741.4c (mg/L) (n＝11, γ＝0.994) and the detection limit was 0.072 mg/L. The influences of the interference substances on the determination were investigated and the proposed method was further applied to the Hep samples determination with satisfactory results.

Key words: heparin, methyl violet, electrochemistry, binding reaction