Simultaneous ultraviolet-visible (UV–VIS) spectrophotometric quantitative determination of Pb, Hg, Cd, As and Ni ions in aqueous solutions using cyanidin as a chromogenic reagent

The use of cyanidin (3, 3 1 4 1 5, 7 – pentahydroxyflavylium chloride) extracted from a tropical plant Hibiscus sabradiffa L. as a chelating reagent for simultaneous spectrophotometric determinations of ions of Pb, Hg, Cd, As and Ni in mixed aqueous solution is reported. The purified extract of the dried calyces of the Roselle plant was characterized and the results compared with literature values. Complexation of the metals ions with cyanidin and scanning through 200-700 nm in a UV –VIS spectrophotometer gave the wavelength of maximum absorption (λmax) of these metal complexes to be 389.6, 360.0, 357.8, 396.8 and 401.0 nm for Pb(II); As(II); Cd(II); Hg(II) and Ni(II) complexes respectively indicating appreciable bathochromic shifts compared to pure cyanidin absorption at 283.2 nm. The effect of pH on the determinations was studied and a pH value of 5 was found to be the optimal. Calibration curve plots of the complexes showed linearity between concentration of 0.1 to 5.0 ppm. This method offer cheap, simple, rapid, sensitive, and eco-friendly technique for simultaneous determination of trace heavy metals in mixed aqueous solutions and have potentials for environmental and biological samples.