Graphene modified Palladium sensor for electrochemical analysis of norepinephrine in pharmaceuticals and biological fluids

A novel voltammetric sensor for the determination of norepinephrine (NE); an important neurotransmitter, has been developed using graphene modified palladium (Pd) sensor. Graphene was synthesized in the laboratory and was characterized by SEM, TEM, XRD and Raman spectroscopic measurements. The electrochemical response of modified sensor towards NE determination was studied by the means of electrochemical impedance spectroscopy, cyclic voltammetry and square wave voltammetry. The modified sensor exhibited excellent electrocatalytic activity for the oxidation of NE, leading to a remarkable enhancement in the peak current and lowering of peak potential. The anodic peak current was found to increase linearly with increasing the concentration of NE using graphene modified Pd sensor in the range 0.0005-0.5 mM in phosphate buffer of pH 7.2 with limit of detection and limit of quantification as 67.44 nM and 224.8 nM, respectively. The detection sensitivities of bare and modified Pd sensors were 0.851 μA mM^-1 and 17.428 μA mM^-1, respectively, revealing the good electrocatalytic properties of graphene modified sensor. The proposed method was successfully applied for the determination of NE in pharmaceutical dosage forms and human urine samples. It was observed that using developed sensor NE can be detected in urine samples even in the presence of high concentration of uric acid.