Fig. 8. (a) Anodic stripping voltammogram of Ni2+ (1–50 ppm) determination with the screen-printed carbon electrode on a Whatman No. 4 paper-based device at a
deposition potential of −0.9 V versus Ag/AgCl. (b) The calibration plot of anodic currents at 180 s of deposition time for determination of the Ni2+ level. Data are
(a) representative of, or (b) derived from, three independent repeats.