In the present study, a new ultrasound assisted extraction (UAE) method was developed for preconcentration of selenite, Se(iv), from sample matrices prior to analysis. The method is based on complex formation between phenoxazine dye, resazurin, and triiodide, I₃⁻, which is produced by oxidation of iodide with Se(iv) in the presence of cetylpyridinium chloride (CPC) at pH 5.0, and then the extraction of the complex into the micellar phase of the extracting agent. The proposed process offers good sensitivity, ease of use and short analysis time. The variables affecting complex formation and extraction efficiency were studied and optimized in detail. Under optimal conditions, a good linear relationship was obtained in the range of 2.5–120 μg L⁻¹ with a detection limit of 0.76 μg L⁻¹. The precision was found to be 3.5% (n: 5, 10 and 40 μg L⁻¹). After preconcentration of a 15 mL sample, a sensitivity enhancement factor of 34.1 was obtained. The method offers good sensitivity, ease of use and short analysis time. Total inorganic Se was determined after the reduction of Se(vi) to Se(iv) using hydrochloric acid. The validation was evaluated by analysis of two standard reference materials (SRMs) and the recovery test. Finally, the method was successfully applied to the determination of inorganic Se in selected samples, and recoveries higher than 93.7% to 103% were obtained.

In this paper, we describe ultrasonic assisted-dispersive solid phase extraction based on ion-imprinted polymer (UA-DSPE-IIP) nanoparticles for the selective extraction of lead ions. Ultrasound is a good and robust method to facilitate the extraction of the target ions in the sorption step and elution of the target ions in the desorption step. The ion-imprinted polymer nanoparticles used in the UA-DSPE-IIP were prepared by precipitation polymerization technique. The ion-imprinted polymer nanoparticles was synthesized using 2-vinylpyridine as a functional monomer, ethylene glycol dimethacrylate as the cross-linker, 2,2′- azobisisobutyronitrile as the initiator, 1,3,4-thiadiazole-2,5-dithiol as the ligand, methanol/dimethyl sulfoxide as the solvent, and lead as the template ion, through precipitation polymerization technique. The IIP nanoparticles were characterized by Fourier transformed infra-red spectroscopy (FTIR), thermogravimetric and differential thermal analysis (TGA/DTA), and scanning electron microscopy (SEM). Box-Behnken design (BBD) was used for optimization of sorption and desorption steps in UA-DSPE-IIP. In the sorption step: pH of solution, IIP amount (mg), sonication time (min) for sorption and in the desorption step: concentration of eluent (mol L⁻¹), volume of eluent (mL), and sonication time (s) for desorption was investigated and optimized by the Box-Behnken design. The optimum conditions for the method were pH of solution: 7.5, sonication time for sorption 7.5 min, IIP amount 24 mg, type and concentration of eluent HCl 1.4 mol L⁻¹, volume of eluent 2.1 mL, and sonication time for desorption 135 s. Under the optimized conditions, the limit of detection and relative standard deviation for the detection of lead ions by UA-DSPE-IIP was found to be 0.7 μg L⁻¹ and <4%, respectively.

A simple and rapid dispersive solid-phase extraction method coupled with furnace atomic absorption spectrometry detection was developed for selective separation and preconcentration of ultra-trace amounts of lead ions using modified magnetic graphene oxide such as the pseudo imprinted polymer sorbent in real water and food samples. Some effective parameters in the extraction of lead were selected and optimized. The optimum experimental conditions of the proposed method were: pH, 5.0; amount of absorbent, 1 mg; eluent type and its volume, 50 μL of 0.4 mol L⁻¹ hydrochloric acid; sample solution volume, 30.0 mL. Under the optimum conditions, a high preconcentration factor of 600 was obtained for 30.0 mL of sample solution. The relative standard deviation for seven 20 ng L⁻¹ replicates of lead was 2.4% and the detection limit was 0.18 ng L⁻¹. The proposed method was applied for the determination of lead ions in real water and food samples, and its accuracy was assessed through the analysis of a certified reference water (ERA 1340) and recovery experiments.