Electrothermal behavior of sodium, potassium, calcium and magnesium in a tungsten coil atomizer and review of interfering effects

The electrothermal behavior of Na, K, Ca and Mg in a 150-W tungsten coil atomizer was investigated in order to gather information about the atomization processes and the underlying factors responsible for chemical interferences of them on atomization of Al, Ba, Cd, Co, Cr, Pb and Yb. The interference effects were discussed considering the thermal stability of the species that could be formed in the condensed phase, the effect of protective gas composition in the atomization process and the pyrolysis temperature curves. Ca is the most serious interferent due to its high thermal stability (up to 1600°C) and to the possibility of double oxides formation. As hydrogen is decisive for the atomization of Na, K, Ca and Mg, some interference processes caused by these elements seem to be related to the competition towards hydrogen present in the protective gas composition. The knowledge of the correct temperature of the tungsten coil surface shows that most strategies for overcoming interferences based on chemical modifiers will fail for Cd and Pb, because tungsten acts as a natural permanent chemical modifier. It seems that in many applications previous separation and masking will be necessary.