Thermogravimetric investigations on the mechanism of decomposition of Pb compounds on a tungsten surface

Tungsten coils are used as electrothermal atomizers in atomic absorption spectrometry (ETA-W), but despite successful applications the atomization mechanism is still obscure. The use of the thermogravimetry (TG) can bring some information on decomposition pathways for atom formation, simulating the drying and pyrolysis steps employed in typical heating program cycles. Thermogravimetric curves of Pb salts with and without chemical modifiers, such as ascorbic, oxalic, tartaric acids, and glucose, or interferents (e.g. NaNO3) were obtained using a lab-made tungsten sample holder in an 90% Ar plus 10% H2 atmosphere usually employed in ETA-W. Intermediaries and residues of the pyrolysis step were characterized by X-ray diffraction. These data allows a better establishment of parameters for ETA-W and can help to find proper conditions to decrease interferences. It was showed that the general decomposition route is the formation of PbO by heating, oxide reduction by H2 in the purge gas followed by volatilization of Pb.