Novel analytical method using reversed-phase dispersive liquid-liquid microextraction for determination of metallic contaminants in edible vegetable oils

In this work, a method based on reversed-phase dispersive liquid-liquid microextraction (RP-DLLME) as sample preparation for the extraction and pre-concentration of Cu, Mn and Ni in edible vegetable oils (chia, flaxseed, sesame, safflower and canola) was developed. For the proposed sample preparation method, a solvents mixture of n-propanol (dispersant, 700 μL) and 1.0 mol L-1 HNO3 (extractant, 300 μL) was injected into the sample (10.0 g) preheated to 80 °C. After flasks were centrifuged (10 min at 5600 g), the sample phase was partially withdrawn using a pipette, and the aqueous phase was transferred to volumetric flask and volume was completed to 5.0 mL, for further elemental determination by F AAS. Some parameters, such as type and volume of dispersive and extraction solutions and HNO3 concentration (extraction solution), were evaluated. During the optimization of RP-DLLME, samples of chia oil were spiked with Conostan® S21+K oil standard. Analytes determination was performed by F AAS using external calibration with aqueous reference solutions. The accuracy was evaluated by recovery tests, which ranged from 92 to 100%, with relative standard deviation lower than 4% for all analytes. Then, the proposed method was applied for various samples of vegetable edible oils. Thus, comparing to conventional methods for metallic contaminants determination in edible oils, RP-DLLME combined to F AAS can be considered simple, low cost, low consumption of reagents and provides LOQs significantly below the limits established by Brazilian legislation for these elements in biodiesel.