Advancements in sample preparation for performing elemental analysis of human hair by inductively coupled plasma mass spectrometry

The determination of minerals and trace elements in human hair is potentially useful for assessing an individual's health status and monitoring occupational and environmental exposure [1,2,3]. Moreover, human hair is a stable matrix that presents numerous advantages for human biomonitoring, such as easy collection, low cost, easy transport and storage, and information about short- and long-term exposure. Consequently, its use in toxicological, clinical, environmental, and forensic investigations is growing and becoming more extensive. On the other hand, owing to the lack of standardized hair analysis procedures (including sample treatment methods), it is difficult to compare and interpret the results (intervals and reference values) from different studies and reach significant conclusions. In particular, recent reviews have revealed that analytical characteristics (detection/quantification limits and accuracy) are scarcely reported. Analyte loss, contamination, and/or interferences may also lead to a decrease in the analytical accuracy of the results. Incomplete decomposition of the hair samples involves an appreciable amount of residual carbon (C) in the resulting sample solution. In inductively coupled plasma spectrometry (ICP) techniques, this leads to the increased signal of some elements by carbon charge transfer reactions, especially for elements that have similar ionization potentials to that of C [4]. Another source of error in hair analysis by ICP with mass spectrometry (ICP-MS) is the interference caused by the residual acidity in the digests, difference between the viscosity and acid concentrations of the calibration and sample solutions, and the presence of polyatomic ions in the plasma [4]. Considering these aspects, the aim of this study was to optimize and validate a fast screening analytical method for the determination of 40 elements (Al, As, B, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cs, Cu, Fe, Ga, K, La, Li, Mg, Mn, Mo, Na, Nb, Ni, P, Pb, Rb, Sb, Se, Si, Sn, Sr, Te, Ti, Tl, U, V, W, Zn, and Zr) in small-size (0.02 g) human hair specimens. The samples were subjected to HNO3/H2O2 (2:1) digestion in an open vessel heated in a water bath and subsequently analyzed by ICP-MS equipped with a collision-reaction interface [4]. This method was used to determine the levels of essential and toxic heavy metals in the hair of children living in the Benishangul-Gumuz region, a Developing Regional State of North-Western Ethiopia [1]. The influence of several factors in the variability of element concentrations in children’s hair (age, sex, body mass index, passive smoking, and eating habits) was also studied [1]. [1] M.L. Astolfi, G. Pietris, C. Mazzei, E. Marconi, S. Canepari, Int. J. Env. Res. Pub. He. 2020, 17, 8652. [2] M.L. Astolfi, C. Protano, E. Marconi, L. Massimi, D. Piamonti, M. Brunori, M. Vitali, S. Canepari, Int. J. Env. Res. Pub. He. 2020, 17, 1911. [3] C. Protano, M.L. Astolfi, E. Marconi, A. Antonucci, S. Canepari, D. Piamonti, M. Brunori, M. Vitali, Biol. Trace Elem. Res. 2020, 197, 89–100. [4] M.L. Astolfi, C. Protano, E. Marconi, L. Massimi, M. Brunori, D. Piamonti, G. Migliara, M. Vitali, S. Canepari, Anal. Methods 2020, 12, 1906–1918.