Previous studies on brazilein have shown color changes in response to pH variations. This study further explores the potential of ethanol extract from sappan wood (Caesalpinia sappan L) as a metal detection agent. The research supports the Sustainable Development Goals (SDGs), particularly SDG-6 (Clean Water and Sanitation), by advancing environmentally friendly detection techniques and contributing to environmental and public health monitoring.

Through visual observation and UV analysis, color changes in the sappan wood extract can be clearly observed. Computational analysis was also conducted to evaluate the stability and formation energy of the resulting complexes. The sappan wood extract initially appears yellow; when Pb(NO₃)₂ and Pb(OAc)₂ are added, the color changes to pink, with maximum absorbance at λmax = 462 nm and λmax = 512 nm.

The addition of FeCl₃ and Fe(NO₃)₂ produces a cream color, with maximum absorbance at λmax = 436 nm and λmax = 454 nm. Meanwhile, the addition of CuSO₄ results in a peach-colored solution, with maximum absorbance at λmax = 444 nm and λmax = 500 nm.

Stability analysis of chelate formation, calculated using Density Functional Theory (DFT), shows that the Fe complex is the most stable, with the highest interaction energy E(2) of 1907.83 kcal/mol. The Cu complex also demonstrates high stability, with an energy value of 824.90 kcal/mol, while the Pb complex is less stable, with an energy value of 296.71 kcal/mol.

Author: Prof. Dr. Nanik Siti Aminah, M.Si.

Link: https://scholar.unair.ac.id/en/publications/new-potential-for-colorimetricvisual-detection-of-pb-fe-and-cu-me/fingerprints/?sortBy=alphabetically

Rasayan Journal of Chemistry, Vol. 18, No. 4, pp. 2556–2563, October–December 2025

Article type: Research article

This article is a repost from the Popular Scientific Articles page of Universitas Airlangga (UNAIR) and has been adapted for publication on the Chemistry UNAIR page.
Original source: “New Potential for Colorimetric/Visual Detection of Pb, Fe, and Cu Metals Using Caesalpinia sappan L Extract and Stability Analysis via DFT Calculations”