Multielemental analysis of oils and animal fat by using deep eutectic solvents assisted by an aerosol phase extraction procedure

Abstract

In the present study, thirteen elements (Ag, Al, Ba, Cd, Cr, Cu, Fe, K, Li, Mg, Mn, Ni, Pb) have been extracted from used cooking oils, olive oils and animal fat. Either inductively coupled plasma optical emission spectrometry (ICP-OES) or tandem mass spectrometry (ICP-MS/MS) have been chosen as detection techniques. Due to the difficulty of directly introducing highly viscous organic samples into the spectrometer, a fast dispersive liquid – liquid aerosol phase extraction (DLLAPE) method has been selected to isolate the analytes from the sample matrix. The DLLAPE is based on the generation of an aerosol from the extracting phase with the help of a pneumatic nebulizer. This high velocity aerosol impacts and penetrates in the liquid sample. Consequently, the liquid – liquid exchange surface area becomes high, thus leading to high extraction yields. A hydrophilic deep eutectic solvent (DES) consisting of choline chloride and ethylene glycol (1:2 mass ratio) has been selected as the extracting solvent. Prior to undertaking the experiments, the extraction method has been evaluated in terms of precision under suitable conditions. In comparison with conventional methods based on sample digestion, sample dilution and shot analysis or extraction assisted by vortex agitation, the DLLAPE shows several advantages, because it is faster, and it provides lower limits of detection than the reference methodologies. The procedural limits of quantification for the determined elements with the DLLAPE in ICP-OES were 0.046 (Ag), 0.396 (Al), 0.013 (Cd), 0.033 (Cr), 0.040 (Cu), 0.20 (Fe), 0.026 (K), 0.026 (Li), 0.33 (Mg), 0.013 (Mn), 2.64 (Ni) and 0.53 (Pb) mg kg−1. Meanwhile, pLOQ in ICP-MS/MS lowered by roughly one order of magnitude. The accuracy of the aerosol phase extraction method has been evaluated through the determination of the recoveries for four representative analytes (Ca, Cu, Mg and Ni) from spiked real samples. For these elements, recovery has taken values of (100 ± 20)%. Moreover, a comparison of the multielemental concentration obtained with conventional methods (c.a., sample dilution and shot ICP analysis and liquid-liquid extraction using a vortex agitator) against that measured with the DLLAPE has been carried out. Multiemelemental concentrations have been obtained for real samples and the found levels have been similar to those encountered in previously published works.