Linear Sweep Polarographic Determination of Chondroitin Sulfate using Toluidine Blue as Electrochemical Probe

An electrochemical method for the determination of chondroitin sulfate (CS) was established by using toluidine blue (TB) as electrochemical probe. In pH 5.0 Britton–Robinson (B-R) buffer solution, TB had a well-defined second order derivative linear-sweep polarographic reductive wave at –0.04 V (νs. SCE). The addition of CS to the TB solution resulted in the decrease of the peak current without the shift of the peak potential, which was because of the interaction of CS and TB via electrostatic attraction. A supramolecular complex was formed in the mixed solution, and this resulted in the decrease of both the diffusion coefficient of TB and the peak current. The conditions of binding reaction and electrochemical detection were optimized. On the basis of the decrease of the reductive peak current, a novel electrochemical method for the quantitation CS was developed with the linear range as 6.0–30.0 mg l–1 and the linear regression equation as ΔIp? (nA) = 92.96C (mg l–1) –500.4 (n = 16,γ = 0.9909). The established method was further applied for the determination of synthetic samples, and satisfactory results were obtained. The binding constant (βs) and the binding number (m) of CS with TB were calculated as βs = 2.57 × 1010 and m = 2 using the voltammetric data.