Natural deep eutectic solvents (NADES) were introduced for the extraction of free selenoamino acids from lyophilized and powdered milk samples. Different NADES were evaluated, and lactic acid:glucose (LGH) showed the highest selenium recoveries. Selenium analysis was performed by inductively coupled plasma mass spectrometry (ICP MS). Se-NADES analysis in ICP MS was optimized according to the radio frequency power and nebulization gas flow rate. Se-NADES extraction was optimized by an experimental design. LGH dilution, LGH volume, sample quantity, and ultrasound time were factors influencing the extraction. Seleno-amino acids were determined by liquid chromatography-ICP MS. After optimization, the limits of detection obtained were 7.37, 8.63, and 9.64 µg kg -1 for selenocysteine, selenomethionine, and seleno-methylselenocysteine, respectively. The NADES-extraction is a green procedure with 2 penalty points in the EcoScale. The method was applied to the analysis of powdered milk, lyophilized Se-fortified sheep milk, and ERM-BD151 skimmed milk powder.
The proposed methodology is based on the preconcentration of Pb 2+ on oxidized carbon xerogel, a porous material of low density and high surface area. Adsorbed Pb 2+ was eluted with HCl, followed by complexion with dithizone in ethanol-water solution and determined by UV-visible spectrophotometry in a continuous flow system (FI). Variables such as pH, type of eluent, eluent concentration, type of complexing solvent, concentration of complexing reagent and flow rates were optimized. The proposed system reached an enrichment factor of 50, with 5 mL of sample. Detection limit was of 0.9 g L-1 , with a precision of 7.8% (n=10). The proposed system was successfully applied to the determination of Pb in tap water from San Juan city, Argentina.
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