Potentiometric sensors selective for Cu(II) determination in real water samples and biological fluids based on graphene and MWCNTs modified graphite electrodes

Abstract

Three newly synthesized Cu(II) ion selective electrodes based on 1,8-dihydoxyanthraquinone (DHAQ), as an ionophore, have been developed. Sensor I was modified with DHAQ only, while sensors II and III were modified with graphene and multi-walled carbon nanotubes (MWCNTs), respectively, in addition to DHAQ to improve conductivity and transduction of chemical signal to electrical signal. Under optimized conditions, the electrodes I, II and III revealed Nernstian slopes of 29.78 ± 0.17, 30.25 ± 0.12, and 30.55 ± 0.19 mV decade^-1, respectively, at 25±1° C covering a wide concentration range from 1 × 10^-6 to 1 × 10⁻¹ mol L^-1 for sensors I and II and from 1 × 10^-5 to 1 × 10⁻¹ mol L^-1 for sensor III with detection limit values of 8 × 10⁻⁷, 5 × 10⁻⁷, and 3.3 × 10⁻⁶ mol L^-1, respectively. The response of the proposed electrodes was very fast and independent of pH in the range of 2.4-6.5 and the response mechanism was studied using IR, SEM and EDX analyses. Selectivity coefficients were determined by applying separate solution method (SSM) and matched potential method (MPM), where the obtained values indicated the good discrimination of Cu(II) from other cations by the proposed sensors. The developed sensors were used successfully for quantitative determination of Cu(II) ions in different matrix of spiked real water samples and biological fluids (urine and serum). These sensors were also used successfully as indicator electrodes in the potentiometric titration of Cu(II) with EDTA.