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| Ružičková S., Jankovská E., Koller L. |
| A NEW SPECTROMETRIC TANDEM TECHNIQUE FOR DIRECT ANALYSIS OF SOLID SAMPLES |
Abstract
A new technique for direct analysis of solid samples, based on evaporation of solid sample by high current arc discharge between carrier and counter electrodes in a cell for production of aerosol followed by an excitation of the aerosol in a separated plasma source has been studied. A water-cooled cell for the production of vapours of solid samples has been designed and connected with the plasma source by Marinković. Argon is used as transport gas. Emitted radiation from plasma source is registered by a Polyvac System BV-953 spectrometer made by Hilger Analytical Ltd., controlled by a PC using PC PLUS programme. The choice of studied elements depends on adjusted channels of the spectrometer: B, Be, Ca, Cr, Cu, Ni, Pb, Si, V and Zr. The basic experiments have been carried out with model mixtures prepared from element oxides (1000 ppm of each element) and graphite powder. Evaporation curves and radial distribution of spectral line intensity of the studied elements in the plasma have been measured and evaluated. Radiation from the plasma source projected on the entrance slit of the spectrometer has a shape of a disc. The centre of the disc is represented by the radiation from the hot core of the plasma, whereas the border part of the disc represents radiation from the cooler surface layers of the plasma. Vertical micrometric translation of the plasma source enables to define any layer of the plasma by the entrance slit for recording radiation. This layer is characterised by distance r from the centre of the plasma. As the radial distribution of all signals in the plasma is marked, the evaporation curves of elements are depicted in three-dimensional diagrams. On the basis of these results the optimum plasma layer was chosen for registration of radiation. Influence of the shape and properties of carrier electrode on spectral line intensities have been investigated. Electrodes made of materials with higher electrical resistance and lower thermal conductivity provide higher spectral line intensities but the shape of electrodes is also important. Electrodes with a small cup for sample introduction enable to reach higher signals than electrodes with large cup. It is due to better heating up of small cup of the electrode by arc discharge. The increase in signals is more significant for low volatile elements if electrodes with small cup are used. For further experiments electrodes with small cup have been used.
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| Keywords: atomic emission spectrometry|direct analysis of solid samples|separated evaporation and excitation of elements| |
| No 2 (2002), p. 189-195 |
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