Amperometry of heparin polyion using a rotating disk electrode coated with a plasticized PVC membrane

Electrochemical method of detection of heparin polyion wits developed based on voltammetry of heparin on a rotating glassy carbon (GC) electrode coated with a plasticized PVC membrane. The membrane was deposited on the GC disk by spin-coating technique using a mixture of solutions of PVC in tetrahydrpfuran, and 1,1'-dimethylferrocene (DMFc) and hexadecyltrimethylammonium tetrakis(4-chlorophenyl)borate (HTMATPBCI) in o-nitrophenyl octyl ether. UV/vis reflection spectrometry was used to evaluate the membrane thickness, which exhibits a linear correlation with the membrane resistance measured by impedance spectroscopy. It is shown that this electrode can be used for amperometric or coulometric detection of heparin in aqueous samples of medically relevant concentrations (1 - 10 U mL(-1)), with a detection limit of 1.4 U mL(-1). Evidence is provided indicating that the current determining step is the reversible adsorption of the ion-pair of heparin polyion with HTMA(+) cation at the membrane/aqueous electrolyte interface, which is driven by oxidation of DMFc at the GC/membrane interface.