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\bibitem{Ro_etal1999} {\textquotedblleft}\textit{Determination of low-Z elements in individual environmental particles using windowless EPMA}{\textquotedblright}. Ro C-U, Os{\'a}n J, Van Grieken R, Analytical chemistry \textbf{71}, 1521 (1999).   http://doi.org/10.1021/AC981070F

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