Multielement determination in medicinal plants using electrothermal vaporization coupled to ICP OES

Abstract

Electrothermal vaporization (ETV)-inductively coupled plasma optical emission spectrometry (ICP OES) is proposed for multielement determination in powdered medicinal plants. Simultaneous determination of As, Cd, Cr, Cu, Mn, Ni, Pb and Zn was performed in 10 herbs consumed in Brazil. Heating of the ETV system and the influence of carrier gas flow rate, modifier gas (Freon R12, CCl₂F₂) flow rate and sample mass were evaluated and adjusted to obtain the best signal/noise ratio. Temperatures of 300 °C and 1800 °C were used for pyrolysis and vaporization, respectively. Freon has a strong influence on the pyrolysis and vaporization temperatures and the sensitivity. Although the partial elimination of the sample matrix and Freon can act to minimize matrix effects, standard addition calibration was necessary for direct element determination in solid samples. The accuracy of ETV-ICP OES measurements was evaluated by analysing two certified reference materials (NIST 1515 – Apple Leaves and NIST 1574 – Peach Leaves), and the comparison of results obtained by solution nebulization ICP OES (NEB-ICP OES) for acid decomposed samples. The results were in good agreement (t-test at the 95% confidence level) with certified values and those obtained by NEB-ICP OES. Precision was better than 20%, considering the standard deviation of five replicates, and limits of detection and quantification varied from 0.01 to 0.48 and 0.03 to 1.60 μg g⁻¹, respectively. The proposed method allows the simultaneous determination of As, Cd, Cr, Cu, Mn, Ni, Pb and Zn in medicinal plants in less than 5 min, including the sample preparation step.