In situ-produced CO₂-assisted dispersive liquid–liquid microextraction for extraction and preconcentration of cobalt, nickel, and copper ions from aqueous samples followed by graphite furnace atomic absorption spectrometry determination

Abstract

In the present work, a new microextraction technique, namely in situ-produced CO₂-assisted dispersive liquid–liquid microextraction was introduced for the extraction and preconcentration of cobalt, nickel, and copper from aqueous samples followed by graphite furnace atomic absorption spectrometry detection. The proposed method relies on the CO₂ gas produced due to a chemical reaction as the disperser agent instead of the disperser solvent used in the conventional dispersive liquid–liquid microextraction. Initially, a solid mixture of tartaric acid and sodium bicarbonate was placed in the bottom of a dry conical glass test tube. Then µL level of 1,1,2,2-tetrachloroethane as the extraction solvent was added into the tube. An aqueous solution of the analytes containing sodium diethyldithiocarbamate (as chelating agent) was transferred into the tube. The reaction between tartaric acid and sodium bicarbonate was immediately occurred, and the produced CO₂ led to dispersion of the extraction solvent as tiny droplets into the sample which resulted in extraction of the analytes into the organic solvent. The cloudy solution was centrifuged, and the sedimented phase was analyzed by the instrumental analytical method. Under the optimum conditions, the calibration curves were linear in the ranges of 20–300, 20–200, and 15–250 ng L⁻¹ for Co²⁺, Ni²⁺, and Cu²⁺, respectively. Repeatability of the proposed method, expressed as relative standard deviation, ranged from 2.3 to 4.6 and 4.5–5.6% for intra- and inter-day (n = 6, C = 50 ng L⁻¹) precisions, respectively. Moreover, the detection limits and enrichment factors of the selected analytes were obtained in the ranges of 6.2–12 and 139–150 ng L⁻¹, respectively. The accuracy of the developed procedure was checked by analyzing NRCC-SLRS4 Riverine water as a certified reference material. Finally, the proposed method was successfully applied for the simultaneous analysis of the selected analytes in environmental water and fruit juice samples. The relative recoveries obtained for the analytes in the spiked samples were within in the range of 84–107%.