A combination of nordihydroguaiaretic acid as an electron transfer mediator and multi-walled carbon nanotubes for simultaneous electrocatalytic determination of noradrenaline, uric acid, and tryptophan

A sensitive and selective electrochemical method for determining noradrenaline (NA) was developed using an electron transfer mediator, nordihydroguaiaretic acid (NDGA), electrodeposited on multi-walled carbon nanotubes (MWCNT). Nordihydroguaiaretic acid MWCNT modified GCE (NDGA-MWCNT-GCE) proved to have an excellent electrocatalytic activity for the oxidation of NA in a phosphate buffer solution (pH 7.0). The cyclic voltammetric responses of NDGA-MWCNT-GCE at various potential scan rates show a characteristic shape typical of an EC catalytic process. The kinetic parameters such as electron transfer coefficient, a, and catalytic electron transfer rate constant, k', for the oxidation of NA at the NDGA-MWCNT-GCE surface were estimated using a cyclic voltammetry method. The diffusion coefficient of NA was also estimated using chronoamperometry. The plot of peak current versus NA concentration was constituted of two linear segments with different slopes, corresponding to two different concentration ranges of 2.0-28.0 mu M and 28.0-310.0 mu M, using a differential pulse voltammetric method (DPV). The average voltammetric peak current and the precision estimated in terms of the coefficient of variation for repeated measurements (n = 7) of 3.7 mu mol L-1 NA at NDGA-MWCNT-GCE were obtained as 0.48 mu A and 4.2% respectively. At the modified electrode surface, the peaks of DPV for NA, uric acid (UA) and tryptophan (Trp) were clearly separated from each other when they co-existed in solution. The modified electrode was used to determine NA in an injection solution. The results obtained are in very good agreement with those declared in the label of the pharmaceutical products.