Microextração líquido-líquido em fase reversa para a determinação de metais em óleo diesel e óleos vegetais por espectrometria de fluorescência de raios-X por dispersão de energia.

Abstract

X-ray fluorescence spectrometry (XRF) has been widely used for multielement determination in various samples. However, when quantifying inorganic species to trace amounts is required, separation and preconcentration procedures are often used to reduce interference and increase sensitivity. Liquid phase microextraction (LPME) is one of the most well-known and applied pretreatment techniques in various methods for analyzing traces due to its simplicity, speed, and ease of automation. The three main categories of LPME are single-drop microextraction (SDME), dispersive liquid-liquid microextraction (DLLME), and liquid phase microextraction of hollow fiber (HF-LPME). Two methods were developed using reversed-phase liquid-liquid microextraction (RP-LLME) combined with energy dispersion X-ray fluorescence spectrometry (EDXRF). The first method is based on vortex-assisted reverse-phase liquid-liquid microextraction (RP-VALLME) to determine Cu, Mn, Ni, and Pb in diesel oil samples by EDXRF. Nitric acid solution was the extraction phase. After centrifugation, the aqueous phase was placed into a filter paper disc for EDXRF determinations. The following variables were optimized: type of extraction phase solution (HNO3), extraction phase concentration (0.075 mol L-1), stirring time (45s), and sample volume (5.0mL). The limits of detection and enrichment factors were, respectively: 14 μg L-1 and 34 (Cu), 8 μg L-1 and 62 (Mn), 10 μg L-1 and 59 (Ni), and 7 μg L-1 and 64 (Pb). The method's relative standard deviation (RSD, %) for each element (200 μg L-1 and 400 μg L-1) ranged from 2.1 to 6.4%. The proposed procedure was efficiently applied to determine the four analyses in diesel oil samples. The second method used dynamic RP-LLME to prepare edible oil samples for subsequent determination of Cd, Cr, Mn, and Ni by EDXRF. The microextraction procedure is based on a system in which the donor phase flows through the extractor solvent contained in an extraction chamber. Then, the enriched phase is deposited in filter paper and subjected to detection. Type and concentration of extractor solution (HNO3 0.1 mol L-1), sample flow (10.0 mL min -1), and extraction time (15 min) were optimized parameters. The following limits of detection and enrichment factors were obtained, respectively: 6 μg kg-1 and 100 (Cd), 7 μg kg-1 and 65 (Cr), 8 μg kg-1 and 82 (Mn), and 11 μg kg-1 and 74 (Ni). The proposed method was applied to determine the elements in soybean, sunflower, corn, and canola oils samples. The results were compared with those obtained by inductively coupled plasma optical emission spectrometry (ICP OES). The methods developed are an excellent alternative for determining elements in oil samples due to the advantages obtained, such as simplicity, speed, little waste generation, sensitivity, and the possibility of automation and miniaturization.