ELECTROTHERMAL ATOMIZATION OF SILVER IN GRAPHITE FURNACES .2. EFFECTS OF COPPER, ASCORBIC-ACID AND TRITON X-100

The effects of copper, ascorbic acid and Triton X-100 on the atomization process of Ag are presented as a function of the initial mass of analyte and the heating rate of atomization. In general, a double pulse structure is detected, at a heating rate of 300 K s(-1), in the absorbance profile and its time derivative. This behavior shows up in the Arrhenius plots as two temperature regions of atomization. In the presence of Cu and Triton X-100, a low atomization energy E(a) is obtained in the low temperature region and a high value of E,, which approaches the heat of vaporization of Ag, is obtained in the high temperature region. However, in the presence of ascorbic acid, two low desorption energies are obtained in both temperature regions, suggesting a higher dispersion of particles owing to the presence of a higher number of active sites. At a heating rate of 700 K s(-1), a single atomization step with an atomization energy of 233 kJ mol(-1) and a first kinetic order of release is detected in the presence of Cu. However, in the presence of ascorbic acid and Triton X-100, two temperature regions of atomization are obtained from the Arrhenius plots, even though the absorbance profiles look continuous. In these cases, a mass dependent E(a) is obtained in the low temperature region, and a low E(a) with a first kinetic order of release is obtained in the high temperature region. In summary, the low value of E(a) indicates vaporization from disperse particles, whereas the mass dependent, higher value of E(a) indicates atomization from small clusters, the size and energy of which increase as the initial mass of Ag increases. The structure of the absorbance profiles and their time derivatives, and also the behavior of the Arrhenius plots, correlate well with those predicted by the two-precursor atomization model proposed in our previous work [1].