Analysis of children modelling clay (toy) using inductively coupled plasma-based methods

Abstract

This work proposes the application of a Doehlert design to optimize dilute HNO3 and H2O2 concentrations employed for the digestion of samples of modelling clay for children (used as toy). Inductively coupled plasma-based (ICP) methods were employed to determine 22 inorganic constituents (Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, S, Sb, Se, Sr, V and Zn) in children's modelling clay samples. The limits of quantification (LoQ) obtained were between 0.003 mg kg-1 (Cd, Co and Sb) and 0.54 g kg-1(Ca) employing ICP-based methods. The accuracy and precision of the methods were evaluated by analysing the certified reference materials (CRMs) oyster tissue (NIST 1566b), rice flour (NIST 1568b), peach leaves (NIST 1547) and tomato leaves (NIST 1573a), along with addition and recovery tests. The children's modelling clay samples presented concentrations of As, Ba, Cd, Cr, Pb, Sb and Se in agreement with the maximum values established by National Institute of Metrology, Quality and Technology (Instituto Nacional de Metrologia, Qualidade e Tecnologia - INMETRO). However, for other elements it were obtained concentrations within the following ranges: Al (0.83 ± 0.12–2.91 ± 0.04 g kg−1), Ca (16.09 ± 0.20–24.56 ± 1.00 g kg−1), Cu (< 0.30–30.01 ± 2.11 mg kg−1), Fe (< 5.3 - 13.21 ± 3.94 mg kg−1), K (1.31 ± 0.33–33.47 ± 0.75 g kg−1), Mg (0.90 ± 0.04–1.36 ± 0.05 g kg−1), Mn (3.32 ± 0.10–121.05 ± 1.88 mg kg−1), Na (12.07 ± 0.88–36.77 ± 0.50 g kg−1), Sr (4.23 ± 0.47–22.43 ± 6.95 mg kg−1), P (1.00 ± 0.13–57.43 ± 0.88 g kg−1), V (0.25 ± 0.07–1.15 ± 0.19 mg kg−1), S (3.57 ± 0.77–48.49 ± 1.02 g kg−1), Zn (< 4.4–11.82 ± 0.49 mg kg−1), Co (0.020 ± 0.002–0.060 ± 0.020 mg kg−1) and Ni (< 0.03–1.33 ± 0.46 mg kg−1). These elements have no minimum and maximum limits established by legislation for children's modelling clay so, a comparison was not possible. The ICP-based methods presented an efficient routine application in the analysis of modelling clay.