A new electrochemical method for the determination of chondroitin sulfate based on its supramolecular interaction with cupferron-lead(II) complex

In this paper, the interaction of cupferron (Cup) and lead (II) complex [Cup-Pb (II)] with chondroitin sulfate (CS) was investigated by linear sweep voltammetric method. In the selected medium of pH 5.5 (acetic acid-hexamine buffer solution), Cup can interact with Pb (II) to form a stable complex of [Cup-Pb(II)], which has a sensitive second order derivative polarographic reductive peak at -0.64V (vs.SCE). After the addition of CS into Cup-Pb (II) complex solution, the reductive peak current decreased without any shift of the peak potential and no new peak appeared, which indicated that an unelectroactive supramolecular complex of CS with [Cup-Pb(II)] was formed. The binding reaction conditions were carefully investigated. Under the optimal conditions, the interaction mechanism was discussed. The decrease of reductive peak current was directly proportional to the CS concentration, thus a new quantitative determination method for CS was established with the linear regression equation as ΔIp″(nA)=36.97 C/mg L-1+12.45 (n=10, γ=0.995). The effects of other substances on the determination were carefully investigated and three synthetic samples were determined with satisfactory results. The binding constant (βs) and the binding number (m) of CS with [Cup-Pb(II)] complex were calculated from the voltammetric data with the results as βs=1.89×1010 and m≈2.5