Potentiometric sensors selective for Cu(II) determination in real water samples and biological fluids based on graphene and multi-walled carbon nanotubes modified graphite electrodes

Three newly synthesized Cu(II) ion selective electrodes based on 1,8-dihydoxyanthraquinone (DHAQ), as an ionophore; have been developed. Carbon paste electrode has been modified with DAHQ (sensor I), graphene and DHAQ (sensor II) and multi-walled carbon nanotubes (MWCNTs) and DHAQ (sensor III), in order to improve the 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 degrees C covering a wide concentration range from 1x10(-6) to 1x10(-1) mol L-1 for sensors I and II and from 1x10(-5) to 1 x 10(-1) mol L-1 for sensor III with detection limit values of 8x10(-7), 5x10(-7), and 3.3x10(-6) mol L-1, respectively. The response of the proposed electrodes is very fast and independent of pH in the range of 2.4-6.5 and the response mechanism is studied using IR, SEM and EDX analyses: Selectivity coefficients have been determined by applying separate solution method and matched potential method, where the obtained values indicated the good discrimination of Cu(II) from other cations by the proposed sensors. The developed sensors have been 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 have also been used successfully as indicator electrodes in the potentiometric titration of Cu(II) with EDTA.