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\bibitem{Schelles_etal1996} {\textquotedblleft}\textit{The use of a secondary cathode to analyse solid non-conducting samples with direct current glow discharge mass spectrometry: potential and restrictions}{\textquotedblright}. Schelles W, de Gendt S, Maes K, Van Grieken R, Fresenius{\textquoteright} journal of analytical chemistry \textbf{355}, 858 (1996).   http://doi.org/10.1007/S0021663550858

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