Desorption mechanism of arsenic from non-pyrolytic graphite, pyrolytic graphite and pyrolyzed ascorbic acid in electrothermal atomic absorption spectrometry

It was found that Arrhenius plots were composed of two straight portions fo r As deposited on the PG and NPG furnace walls and of one straight portion for that on active carbon formed from the pyrolysis of ascorbic acid at a l ow-temperature pyrolysis. To correct the absorbance of the first peak for t hat of the second peak, the absorbance corresponding to the second peak in the period of the first peak was evaluated by extrapolating the straight li ne for the second peak to each atomization time. The activation energy (E-a ) for the first peak depended on the ratio of the edge carbon species in gr aphite as the condensed phase based on Raman spectrometry. At a high temper ature pyrolysis, the first straight portion disappeared and the E-a for the second straight portion increased in the PG and NPG furnaces. The existenc e of two types of atomization mechanisms as the first atomization correspon ding to the desorption of As binding to active sites and the second atomiza tion corresponding to the desorption of As intercalated within the graphite structure are proposed. On the active carbon, an increase in E-a was also observed, which is in agreement with that observed at the high-temperature pyrolysis in the graphite furnaces.