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\bibitem{Spolnik_etal1999} {\textquotedblleft}\textit{Determination of trace elements in organic matrices by grazing-emission X-ray fluorescence spectrometry}{\textquotedblright}. Spolnik ZM, Claes M, Van Grieken R, Analytica chimica acta \textbf{401}, 293 (1999).   http://doi.org/10.1016/S0003-2670(99)00471-7

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