A hydrophobic deep eutectic solvent-based microextraction for the determination of ultra-trace arsenic in foods by an electrothermal atomization atomic absorption spectrometry

A hydrophobic deep eutectic solvent-based liquid-phase microextraction approach for the determination of ultra-trace arsenic (total) in foods by an electrothermal atomization atomic absorption spectrometry was developed. Various deep eutectic solvents based on tetraoctylammonium bromide and fatty acids (heptanoic, octanoic, nonanoic, decanoic acids) were studied as extraction solvents for preconcentration of arsenic (V) from mineralizates obtained after a microwave digestion of food samples. Phenomenon of ion-pairs formation between dihydroarsenate and precursor of deep eutectic solvent (tetraoctylammonium) and mass-transfer of the ion-pairs into deep eutectic solvent phase was presented for the first time. The proposed approach allowed to preconcentrate analyte into the deep eutectic solvent phase without the use of additional organic solvents (emulsifier agents or dispersive solvent), chelating and reducing agents. It was found, that the deep eutectic solvent based on tetraoctylammonium bromide and heptanoic acid provided more effective preconcentration of analyte from mineralizates (95% extraction recovery, 57-fold enrichment factor). The obtained limit of detection, calculated as a triple signal-to-noise ratio, was 10 ng L-1. The microextraction procedure was applied for the determination of trace arsenic in rice and wheat grains samples.