Preparation and investigation of green and cheap deep eutectic solvents for determination of essential and toxic metal ions at trace levels in different coffee products

Abstract

In this research, a vortex-assisted hydrophobic deep eutectic solvent-based dispersive liquid phase microextraction (VA-HDES-DLPME) method was developed to extract some essential (Fe, Mn and Zn) and toxic (Cd and Pb) metal ions from coffee products. After the VA-HDES-DLPME method, the amounts of the metal ions in the HDES-phase were determined by flame atomic absorption spectrophotometry (FAAS). For selective extraction of metal ions, five HDESs (as extraction solvent) were prepared and tested according to the ultrasonic-assisted procedure. Some dispersive solvents were investigated to ensure the dispersion of HDES in the sample solution. In the VA-HDES-DLPME method, heating and centrifugation steps were not required to separate the HDES-phase from the sample solution. Key factors were investigated and optimized to achieve selective and rapid extraction of metal ions. Under optimized conditions, the working range of the VA-HDES-DLPME method for metal ions ranged from 0.03 to 280 μg kg−1. The detection limits of Fe(II), Mn(II), Zn(II), Cd(II), and Pb(II) ions were 0.01, 0.27, 0.02, 0.015, and 0.18 μg kg−1, respectively. Relative standard deviation and extraction recovery for five replicate runs of 5 μg kg−1 of metal ions were in the range of 1.3%–1.9% and 94 ± 4%-98 ± 2%, respectively. Validation of the VA-HDES-DLPME method was tested by studies on three reference materials. In the final step, the VA-HDES-DLPME method was successfully applied to microwave digestion of coffee samples using a standard addition method. The obtained quantitative recoveries showed the good accuracy of the method.