Potentials of 3, 31, 41, 5, 7-pentahydroxyflavylium of Hibiscus rosa-sinensis L. (Malvaceae) flowers as ligand in the quantitative determination of Pb, Cd and Cr.

Abstract

3, 31,41,5,7-Pentahydroxyflavylium chloride (cyanidin chloride) was extracted from the flowers of Hibiscus rosa-sinensis L. and blackberry fruits and the purity confirmed by co-chromatography with authentic marker on thin layer chromatography (TLC) and paper chromatography (PC). UV-Visible spectrophotometric determinations of the sample and its Pb (II), Cr (III) and Cd (II) complexes at various pH were carried out. The cyanidin sample absorbs at 530 and 540 nm in methanol and ethanol respectively. A Cyanidin-Pb (II) complex was formed at pH 4.2 (λmax = 555 nm, in methanol). A Cyanidin-Cr (III) complex was formed at pH 1.0 (λmax = 682 nm, methanol and ethanol) while a Cyanidin-Cd (II) complex was formed at pH 3.0 [λmax = 706 nm (methanol) and 679 nm (ethanol)]. All the metal-ligand complexes occur in the ratio of 1:2 and the molar absorptivities are 9.66 x 102, 8.77 x 102 and 9.77 x 102 L.mol-1.cm-1 for Pb, Cr and Cd respectively. Under optimum conditions, the absorbance of the complexes was found to increase linearly with increase in metal-ion concentrations, which corroborated with the correlation coefficient values. The linear range of the calibration graph was 0.1 – 0.5 mM for all the complexes. The results show that cyanidin could be used as a reagent for the spectrophotometric determination of Cr (III), Pb (II) and Cd (II) and by varying the pH, these metals could be determined simultaneously in solution. Key words: Cyanidin chloride, Hibiscus rosa-sinensis, metal - ligand complex, Lead (II), chromium (III), Cadmium (II), spectrophotometric assay.