AN INNOVATIVE SAMPLE PREPARATION PROCEDURE FOR TRACE AND ULTRA-TRACE ANALYSIS ON NONCONDUCTING POWDERS BY DIRECT-CURRENT GLOW-DISCHARGE MASS-SPECTROMETRY

A novel preparation procedure has been developed in order to obtain stable, pin-shaped samples for the elemental analysis of non-conducting powders by direct current glow discharge mass spectrometry (de GDMS): up to now, this technique has been mainly used for the characterization of metals and semiconductors. This work deals with a particular analytical application of the infiltration process, which is frequently employed for producing metal-matrix composites (MMC) for structural applications. The preparation procedure has been tested on germanium dioxide GeO2, an inorganic compound available as high-purity powder. However, the method is, in principle, of general applicability: considering the quality of the results obtained so far, it might be particularly suitable for the detection of traces in powdered, nonconducting materials such as ceramics, bio-inorganics, soils, sediments and for the quantitation of major and minor elements in cases where limited amounts of samples are available (e.g. archaeological findings). The reproducibility of the preparation process is satisfactory: repeated observations by reflected light microscopy (RLM) prove that the oxide grains are homogeneously distributed within a well bounded region of the metallic host matrix. The use of composite pin-shaped samples leads to a rapid stabilization of the plasma discharge, with the consequence that the analytical results are generally superior to those obtained on similar samples prepared by more conventional procedures. In particular, from the ratio of the signals due to Ge+ and GeO+, it can be seen that a large predominance of the former species is quickly established in the plasma, with a correspondingly fast achievement of high detection sensitivities.