Direct analysis of tree rings using laser ablation-ICP-MS and quantitative evaluation of Zn and Cu using filter paper as a solid support for calibration

Abstract

This work demonstrated a quantitative determination of Cu and Zn in tree rings using laser ablation-ICP-MS and the use of quantitative filter paper as a solid support for constructing the calibration curve using aqueous standards. After cleaning the filter paper using 10% v/v HNO₃ for 30 min and drying it, 4 μL of standards is delivered on the filter surface and the results are attained with no normalized data. The analytical curves ranged from 0.5 to 10.0 μg g⁻¹ and 5.0 to 100.0 μg g⁻¹ for Cu and Zn, respectively, and the accuracy of the results was checked not only through Certified Reference Materials (NIST 1573a, tomato leaves and 1575a, pine needles) but also using ICP-MS (Inductively Coupled Plasma Mass Spectrometry) as a reference technique. Then, using such minimalist strategies, this method was applied for evaluating the mass fractions of Zn and Cu directly in tree rings. Three parallel ablation lines were drawn with a 220 μm distance between each one, with the same size of the tree ring samples. The average mass fractions for each tree ring and between the 3 ablated lines were at most ca. 18 and 13 μg g⁻¹ for Cu and Zn, respectively, in Hymenaea courbaril, ca. 4 and 9 μg g⁻¹ for Cu and Zn, respectively, in Tipuana tipu, and ca. 160 μg g⁻¹ and <LQ for Zn and Cu, respectively, in Cavanillesia arborea.