Simultaneous determination of uric acid, xanthine, and caffeine in human urine samples using nickel ferrite/reduced graphene oxide modified electrode

This work describes the synthesis of nickel ferrite/reduced graphene oxide (FN/rGO) and the simultaneous determination of uric acid (UA), xanthine (XT), and caffeine (CF) by using the resultant FN/rGO-modified electrode. The material was characterized by means of X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray microscopy (mapping energy-dispersive X-Ray), adsorption/desorption isotherms of nitrogen, vibrating sample magnetometry, and Raman spectroscopy. The obtained composite with a large surface area comprises reduced-graphene-oxide layers and highly dispersed nickel-ferrite nanoparticles. This composite possesses significant magnetization saturation with a soft magnetic property. The electrocatalytic activity of FN/rGO was studied toward the oxidation of one important purine, UA, and two oxypurines, XT and CF. The electrode successfully separates the voltammetric signals of the three analytes in a trinary mixture and is employed for their simultaneous determination. The peak current varies linearly with the increase of UA, XT, and CF concentration in a range of 4.0-21.5 mu M with detection limits of 1.3, 1.6, and 1.4 mu M for UA, XT, and CF, respectively. The practical application of the modified electrode was demonstrated by simultaneously determining the concentrations of UA, XT, and CF in urine samples with expectable recoveries.