The widespread use of the trace metal chromium in industrial processes and the known toxicity of CrVI species have stimulated interest in chromium speciation analysis. However, some analytical detection systems are not suitable for the quantification of CrIII and CrVI species. In the present study, an aqueous biphasic system (ABS) was employed as an environmentally safe, simple, and economical alternative. The ABS allows the implementation of an efficient separation step before quantifying of the species of interest by flame atomic absorption spectrometry. A robust speciation and preconcentration method was developed, which can be applied to samples with a wide concentration range, without the use of any extractants and interconversion of the species during the procedure. The proposed method was successfully used to determine the chromium species present in tap, treatment plant, river, and electroplating wastewater samples. Recovery percentages of 87.9-107% were achieved, suggesting minor water matrix interference. The proposed method had acceptable limits of detection and quantification of 5.38 and 16.3 µg kg-1, respectively.

Bismuth is a critical metal broadly used in cosmetic, medicine and metallurgy. However, its scarcity in Earth’s crust may impair further applications. An alternative is to recover bismuth from secondary sources. In this work, a methodology to extract bismuth from safety valves of discharged gas cylinders is proposed. Extraction and purification of bismuth were carried out using aqueous two-phase systems (ATPS) prepared with poly(ethylene oxide) polymer or poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) copolymer (L35) and electrolytes (NaNO3, NH4NO3, sodium citrate or Na2SO4). The influence of iodide extractant concentration, tie-line length, electrolyte nature and polymer hydrophobicity on the bismuth extraction behavior were evaluated. Bismuth was significantly recovered in the absence of extractant, and its extraction depends on the ATPS composition, macromolecule and electrolyte nature. After three consecutive extractions bismuth was obtained with high purity (94.7%), resulting on a recovery of 38.5 g of bismuth per 1.00 kg of fusible plug, using L35 + NH4NO3 + H2O ATPS, without any extractant.

Abstract Fe(II) and Fe(III) have distinct chemical and biological functions. Consequently, it is more important to determine the fraction of both oxidation state that knowing the total iron concentration in a sample. However, green methods for iron speciation are still limited. This work uses aqueous two-phase system, a safe alternative to liquid–liquid extraction, to perform the chemical speciation of iron. This method is based on the reaction of Fe(II) with 1,10-phenanthroline extractant, forming a complex of Fe(II)-phenanthroline that concentrates in the top phase of the system. The Fe(III) specie concentrated in the bottom phase of the system. Iron speciation was affected by the electrolyte nature, macromolecule type, quantity of phenanthroline added, and pH. The system formed by PEO1500 + Na3C6H5O7 + H2O at pH 6.00, containing 5.00 mmol kg-1 of phenanthroline, was successfully used to separate the iron species before determination by flame atomic absorption spectrometry. Under these optimal conditions, a separation factor of 233 was obtained between Fe(II) and Fe(III) with extraction percentages of (95.1 ± 1.0)% and (7.68 ± 0.50)%, respectively The proposed method was successfully applied for iron speciation in water samples, and provided recovery percentages ranging between 90 and 106%.

The effects of low contents of acetonitrile (AN) or N,N-dimethylformamide (DMF) on the aggregation of sodium alkyl sulfate surfactants, in the absence and presence of poly(ethylene oxide) (PEO), were investigated using conductivity and isothermal titration calorimetry. The cosolvents slightly changed the critical micellar concentrations and did not alter the critical aggregation concentrations of the surfactants sodium decyl sulfate (DSS) and sodium dodecyl sulfate (SDS) with PEO. However, AN and DMF turned the micellization of the surfactants and their binding to the polymer enthalpically more favorable. For instance, for SDS, the micellization enthalpy, ΔHomic, decreased from close to 0 kJ mol-1 in water to -14.3 kJ mol-1 in the presence of 2.50 mol% AN, and the integral enthalpy change for aggregate formation with the polymer, ΔHagg(int), decreased from -1.1 kJ mol-1 in water to -15.5 kJ mol-1 in the same AN concentration. This was attributed to the modification of the solvation shells of both SDS and PEO by the cosolvent molecules, which reduced the entropic contribution to formation of the aggregates. Consequently, when SDS was replaced with DSS, the AN affected ΔHomic to a lesser extent, with a decrease of 9.1 kJ mol-1, while the ΔHagg(int) values were not altered, highlighting the influence of hydrophobic interactions in the surfactant aggregation process.