Optimization of Vortex-Assisted Dispersive Liquid-Liquid Microextraction for Preconcentration of Copper and Lead Prior to Determination by UV-Vis in Drinking Water
Zimila HE1,2*, Chibindje RHJ1, Mandlate JS1
1Department of Chemistry, Eduardo Mondlane University, Julius Nyerere Av. # 3453, P.O. Box 257, Maputo, Mozambique
2Department of Chemical and Environmental Engineering, The University of Arizona, Tucson, AZ 85721, United States
*Corresponding author: [email protected]
Keywords: vortex-assisted dispersive liquid-liquid microextraction (VA-DLLME), UV-Vis spectrophotometry, copper, lead, drinking water
Submitted: October 16, 2023
Revised: August 2, 2024
Accepted: August 14, 2024
Published: December 21, 2024
Abstract
Several methods have been developed for the analysis of heavy metals in water; however, the majority are unaffordable for many laboratories in developing countries. This work aimed at optimizing and validating the vortex-assisted dispersive liquid-liquid microextraction (VA-DLLME) tandem UV-Vis spectrophotometry for Cu2+and Pb2+ determination in drinking water. The method involves the complexation of Cu2+ and Pb2+ with 8-hydroxyquinoline and dithizone, respectively, followed by extraction and preconcentration under appropriate conditions. VA-DLLME operating conditions (volume of solvents, extraction time, pH, agitation frequency) were screened using the fractional factorial design, and the most important factors were optimized using the response surface approach based on the central composite design. Optimum conditions for Cu2+ determination include ethanol volume of 2000 μL, tetrachloromethane volume of 500 μL, 1 min vortex stirring at 3200 rpm, 5% NaCl, pH 5, and centrifugation time of 8 min. For Pb2+ analysis, the optimum conditions include a methanol volume of 2000 μL, chloroform volume of 350 μL, 1 min vortex stirring at 3200 rpm, pH 5, and centrifugation time of 5 min. The methods offer good linearity with R2 > 0.99, limits of detection and quantification of 0.016 and 0.048 ppm for Cu2+, and 0.004 and 0.016 ppm for Pb2+, respectively. Accuracy assessed as recovery ranged between 90 – 113% for both Cu2+ and Pb2+. The RSD values ranged from 3 – 6% for Cu2+ and 4% – 9% for Pb2+. The methods are simple, selective, precise, and accurate for cost-effective monitoring of Cu2+ and Pb2+ in drinking water.