An on-line system employing switchable-hydrophilicity solvent-based liquid-phase microextraction (SHS-LPME) is described in this work. The method is based on the preconcentration of the species formed between cobalt and the reagent 1-nitroso-2-naphthol (NN), with subsequent detection by digital image colorimetry. The system's operation begins with the on-line mixture of sample, switchable solvent, and an alkaline agent in a reaction coil. Then the mixture is transported to an extraction chamber. The introduction of a proton donor leads to the passage of the solvent to its hydrophobic form, which allows phase separation. The rich phase is then directed to a glass tube, where detection is performed. Octanoic acid, sodium carbonate, and sulfuric acid were used as the extraction solvent, the alkaline agent, and the proton donor, respectively. Under optimized conditions, the method presented a detection limit of 0.8 μg L⁻¹ and an enrichment factor of 41. The precision obtained was 4.8% (20 μg L⁻¹). The accuracy of the method was tested by the analysis of Tomato Leaves certified reference material (NIST 1573a). The method was applied to the determination of cobalt in food, dietary supplements, and water samples. The method is presented as a green alternative and very accessible to the determination of cobalt in the analyzed samples.

BACKGROUND: Sugar‐based surfactants are highly relevant alternative ingredients for food grade formulations. Nevertheless, the design of sustainable manufacturing processes is still ongoing. RESULTS: Sorbitol ester surfactants were synthesized by lipase‐catalyzed esterification in solvent‐free conditions. Octanoic acid was dispersed in a 70 wt% sorbitol aqueous solution (containing the enzyme). The maximal conversion of 23.5 mole % of esterified fatty acid per mole of loaded fatty acid was obtained after 48 h in optimal conditions. The performance of the reactor was affected by both the nature and amount of the reactants and the dispersion state. Detailed structural analysis demonstrated that lipase from Candida rugosa specifically catalyzed the acylation of sorbitol on primary hydroxyl groups. Sorbitol esters accumulated exclusively in the oil phase, which led to easy and efficient product recovery. Oil phase containing the sorbitol esters could be used directly for preparing oil‐in‐water nanoemulsion without adding any other stabilizer. These nanoemulsions exhibited good stability after 7 days storage at 25°C or 60°C. CONCLUSION: A green manufacturing process for food grade oil‐in‐water nanoemulsions was designed involving a lipase‐catalyzed esterification step which produced in situ the required surfactant. Nanoemulsions were prepared without using any other stabilizer. © 2017 Society of Chemical Industry