Magnetic eutectic mixture as extractant for elemental analysis of essential oils combining liquid-phase...

In the present work, a simple, fast, sensitive and accurate method was developed to determine Cd, Cr, Cu, Fe, Mn, Ni, Pb, V, and Zn in essential oil samples at trace levels by inductively coupled plasma optical emission spectrometry (ICP OES). Vortex-assisted dispersive liquid-liquid microextraction (VA-DLLME) was employed to preconcentrate the analytes, with a hydrophilic magnetic eutectic mixture (MEM) acting as the extractant. The MEM used was a mixture of ethylene glycol (EG) and CoCl₂ in a molar ratio of 2:1. The optimal extraction conditions, sample amount, MEM volume and extraction time were determined through two-stage multivariate analysis: the first stage consisted of a 2³ full factorial design, and the second stage was a central composite design. The optimal extraction conditions obtained were: 7.0 g of diluted sample amount, 150 μL of MEM, and 1 min of extraction time. Under these extraction conditions, the analytical method (VA-DLLME/ICP OES) was validated and demonstrated linearity in the range of 10-500 μg kg^-1, excellent precision (RSD ≤7%) and limits of detection in the range of 0.04-1 μg kg^-1. The method accuracy was assessed using a matrix certified reference material (MCRM). Finally, the proposed method was successfully applied to analyze three commercial essential oil samples (eucalyptus, lavender, and tea tree).