RSM-Optimized Ultrasonic-Assisted Extraction for High-Efficiency Recovery of Pb, Cd, and As in Complex Systems

Toxic trace metals such as lead (Pb), cadmium (Cd), and arsenic (As) represent persistent environmental contaminants associated with significant human health risks. Reliable and rapid analytical strategies are therefore essential for toxicological surveillance of consumer and environmental matrices. In this study, a green and process-intensified ultrasonic extraction method was developed for the efficient recovery and determination of Pb, Cd, and As from complex matrices including herbal materials, cosmetic products, beverages, and wastewater, using Atomic Absorption Spectrometry. The approach utilizes ultrasonic cavitation to accelerate metal desorption and mass transfer, enabling rapid extraction under mild conditions with reduced reagent consumption. Galangal was selected as a representative plant matrix to establish and validate the analytical framework. A rotatable central composite design based on response surface methodology was applied to evaluate the influence of nitric acid concentration (0.40-1.20 M), ultrasonic time (5-15 min), and acid volume (20-40 mL) on metal recovery. The statistical model demonstrated strong predictive capability and identified acid concentration and solvent volume as significant factors influencing extraction performance (p < 0.05). Ultrasonic irradiation significantly enhanced metal release from the matrix through cavitation-induced disruption and accelerated diffusion processes. The optimized extraction conditions (0.68 M HNO₃, 11 min ultrasonic time, and 32 mL acid volume) yielded predicted recoveries of 97.13%, 102.09%, and 103.26% for Pb, Cd, and As, respectively, with corresponding experimental recoveries of 95.17 ± 2.37%, 97.50 ± 5.13%, and 98.63 ± 0.25%. The developed method showed a very low matrix effect. The relative expanded uncertainty of metal extraction under optimized conditions ranged from 5.60 to 10.36%, which is within the acceptable criteria (≤15%). Based on the evaluation of trueness through comparison with results obtained from homogeneous proficiency testing (PT) materials, the developed method exhibited acceptable trueness for the quantitative determination of all trace metals, with z-scores less than 2. Application of the method to real samples demonstrated consistent analytical performance across seven galangal varieties and multiple complex matrices, with recoveries ranging from 87.00 to 109.00% (% RSD = 0.08-6.82). These findings demonstrate that ultrasonic processing can provide a rapid, low-reagent, and environmentally responsible extraction strategy for toxic trace metal determination. The developed protocol offers a practical analytical platform for toxicological monitoring, contaminant surveillance, and safety assessment of natural and industrial products.