Speciation analysis of Cr(III) and Cr(VI) in vegetables using a new family of hydrophobic deep eutectic solvents based vortex-assissted liquid-phase microextraction followed by ETAAS

An efficient, simple, cheap and environmental friendly microextraction procedure was developed by hydrophobic deep eutectic solvents based vortex-assissted liquid-phase microextraction (HDES−ALPME) followed by ETAAS detection. A family of DESs were synthesised using l-menthol and different carboxylic acids including hexanoic acid, octanoic acid, decanoic acid and dodecanoic acid and their efficiency in extracting complexed Cr(III) ions was evaluated. The results showed that the DES made of l-menthol and decanoic acid creates a stronger interaction with the analytes and has a better extraction efficiency. After optimising all effective parameters, the proposed procedure showed good linear range of 0.7–70 µg kg−1 with coefficient of determination (r2) 0.9950. The limit of detection was 0.2 µg kg−1 (S/N = 3) for Cr(III) ions, and the high enrichment factor was 277. For measuring the precision, the inter-day and intra-day relative standard deviations (RSDs) were determined to be between 3.6 − 7.2% in three selected concentrations. The potential of the synthesised DES in the separation of Cr(III) from vegetable samples was then examined under optimum conditions. Total chromium (t-Cr) was extracted similarly after reduction of Cr(VI) to Cr(III) with hydroxylamine hydrochloride solution and Cr(VI) concentration was calculated by difference.