Spectrophotowmetric method for mercury determination in cosmetic products using purple sweet potato extract ( Ipomea batatas L.) functionalized silver nanoparticles

Mercury (Hg or Hg2+) is a hazardous heavy metal that is still illegally added to whitening cosmetics, which require rapid, cost-effective, and eco-friendly sensors. This study reports the green synthesis of silver nanoparticles (AgNPs) using purple sweet potato (PSP) extract (Ipomoea batatas L.) as a reducing and stabilizing agent for the spectrophotometric detection of Hg2+ in cosmetics. UV-visible spectrophotometry, FTIR, SEM, and DLS characterized the PSP-AgNPs, confirming spherical nanoparticles with an average hydrodynamic size of 75.86 nm and a characteristic Surface Plasmon Resonance (SPR) peak at 468 nm. The detection mechanism relies on the redox reaction between Hg2+ and PSP-AgNPs, causing a decrease in absorbance and a color change from brown to colorless. Under optimized conditions, the method shows a linear range of 0 to 25 mg/L (R2 = 0.9989). The limit of detection (LOD) and limit of quantification (LOQ) were 0.56 and 1.88 mg/L, respectively. The proposed method demonstrated selective response under the tested conditions and was successfully applied to cosmetic cream samples. Validation against the standard starch-iodide method showed no significant difference, indicating that PSP-AgNPs serve as a reliable alternative sensor for Hg2+ monitoring in cosmetics.