OBSERVATION OF PRE-ATOMIZATION EVENTS ON ELECTROTHERMAL ATOMIZER SURFACES

A brief literature overview of surface chemistry in electrothermal ato mizers is presented. Original data, with regard to condensed phase che mistry, for silver nitrate and cadmium nitrate are shown. The chemical behaviors of these systems are studied during the pre-atomization sta ge with the use of laser desorption time-of-flight mass spectrometry, differential scanning calorimetry and thermogravimetric analysis. Para llel experiments are conducted on graphite and non-graphite surfaces. The collective information from these instruments shows that the conde nsed phase behavior of silver nitrate and cadmium nitrate changes sign ificantly as a function of the substrate. On graphite, the onset of th e decomposition temperature for both cadmium nitrate and silver nitrat e is lowered by more than 130 degrees C. The decomposition of cadmium has been changed from a one-step process on non-graphite surfaces to a two-step process on a graphite substrate. Furthermore, the decomposit ion process for both compounds has been significantly altered from bei ng endothermic on the non-graphite substrate, to becoming highly exoth ermic on graphite. Finally, the process of conversion of metal nitrate s to metal oxides can be followed precisely by laser desorption experi ments.