Detection of Copper (II) and Iron (III) in Aqueous Solutions Using the Spectroscopic Characteristics of Bugnay (Antidesma bunius) Anthocyanins

Abstract

The spectrophotometric characteristics of bugnay (Antidesma bunius) anthocyanins in acidified solutions of copper (Cu²⁺) and iron (Fe³⁺) were investigated after one hour of reaction to determine the changes in their absorbance characteristics. Anthocyanins from bugnay were isolated using solid phase extraction followed by evaporation at 40⁰C. The total anthocyanin content of the extract was determined to be 103.87 + 2.91 mg/L cyanidin-3-O-glucoside equivalents using pH differential method. Maximum absorbance readings at pH 1.0 and 4.5 were determined to be at 520 nm and 350 nm, respectively. Cyanidin-3-glucoside was identified as one of the components of the three pigments in the extract using reversed phase high performance liquid chromatography. At pH 1.0, copper caused greater hypochromic shift of bugnai anthocyanins compared to iron (p<0.01) while iron caused greater hypochromic shift at pH 4.5. Copper also caused hypsochromic shift of anthocyanins from 520 nm to 350 nm at pH 1.0 but not at pH 4.5. Correlation analysis showed a significant moderate positive correlation between mean % hypochromic shift and concentration of copper ions at pH 1.0 (R² = 0.603, p<0.01) and 4.5 (R² = 0.533, p<0.01), and iron at pH 4.5 (R² = 0.638, p<0.01). The spectroscopic characteristics of bugnay anthocyanins at 350 nm and 520 nm can be used as parameters to detect copper and iron in acidic solutions.