Amperometric sensor for heparin: Sensing mechanism and application in human blood plasma analysis

Voltammetric measurements of heparin at a rotating glassy carbon (GQ electrode coated with a polyvinylchloride membrane are reported. A spin-coating technique is used to prepare thin membranes (20 - 40 mu m) with a composition of 25% (w/w) PVC, 1,1'-dimethylferrocene as a reference electron donor for the GC I membrane interface, nitrophenyl octyl ether (o-NPOE) or bis(2-ethylhexyl) sebacate (DOS) as a plasticizer, and hexadecyltrimethylammonium tetrakis(4-chlorophenyl) borate (HTMATPBCl) or tridodecy1methylammonium tetrakis(4-chlorophenyl) borate (TDMATPBCI) as a background electrolyte. It is shown that the electrodes coated with either the HTMA'/oNPOE (DOS) or TDMA(+)/(O)-NPOE (DOS) membrane provide a comparable amperometric response towards heparin (1 - 10 U mL(-1)) in the aqueous solution of 0.1 M LiCl. However, only the membranes formulated with TDMATPBCl can be used for an amperometric assay of heparin in human blood plasma with a detection limit of 0.2 U mL(-1). Effects of membrane composition, heparin concentration, rotation speed and sweep rate on the voltammetric behavior of heparin provide some insight into the sensing mechanism. Theoretical analysis of the amperometric response is outlined, and the numeric simulation of the voltammetric behavior is presented.