Stir bar sorptive extraction and high-performance liquid chromatography-fluorescence detection for the determination of polycyclic aromatic hydrocarbons in Mate teas

A simple procedure based on stir bar sorptive extraction (SBSE) and high-performance liquid chromatography-fluorescence detection (HPLC-FLD) is presented for the determination of 15 polycyclic aromatic hydrocarbons (PAHs) in herbal tea prepared with Mate leaves (Ilex paraguariensis St. Hil.). The influence of methanol and salt addition to the samples, the extraction time, the desorption time and the number of desorption steps, as well as the matrix effect, were investigated. Once the SBSE method was optimised (10 mL of Mate tea, 2 h extraction at room temperature followed by 15 min desorption in 160 μL of an acetonitrile (ACN)-water mixture), analytical parameters such as repeatability (≤10.1%), linearity (r2 ≥ 0.996), limit of detection (LOD, 0.1-8.9 ng L−1), limit of quantitation (LOQ, 0.3-29.7 ng L−1) and absolute recovery (24.2-87.0%) were determined. For calibration purposes, a reference sample was firstly obtained by removing the analytes originally present in the lowest contaminated Mate tea studied (via SBSE procedure) and then spiked at 1-1200 ng L−1 range. The proposed methodology proved to be very convenient and effective, and was successfully applied to the analysis of 11 Mate tea samples commercialised in Brazil. The results of the commercial Mate tea samples found by the SBSE approach were compared with those obtained by liquid-liquid extraction (LLE), showing good agreement.