Effect of ascorbic acid and sucrose on electrothermal atomic absorption signals of indium

Abstract

A significant enhancement of sensitivity with the formation of an unresolved double peak signal was observed for indium when deposited in a pyrolytic graphite (PG) furnace pyrolysed with an organic matrix solution and when deposited in a bare PG furnace as a matrix-added solution, such as ascorbic acid and sucrose. As the pyrolysis temperature increased, the integrated absorbance increased owing to an increase in absorbance at the second peak. The temperature at the second peak remained nearly constant. Integrated across the maximum the integrated absorbance decreased at the decrease in absorbance at the second peak which was shifted to low temperature. The treated PG furnace gave better thermal stability for the effect of pyrolysis temperature for In atomization, whereas the organic matrix additive did not. The double peaks were analysed using Arrhenius plots in the treated PG furnace with a low pyrolysis temperature. The same atomizing species, smaller sized droplets of In(I), on either active sites or in the thermally stable amorphous carbon were attributed to the species in the rate-determining step for the first and second signals, respectively, in the treated PG furnace with a low pyrolysis temperature. With the matrix additive, the two atomizing species, In₂O(g) and smaller sized droplets of In(I) on active sites, were attributed to the first and second signals, respectively. When the pyrolysis temperature increased, the atomizing species in the matrix additive did not change to the larger sized droplets of In(I) except in the treated PG furnace. It was concluded that smaller sized droplets dispersed on the active sites vaporize easily before the larger sized droplets were formed because of a decreased probability of movement due to interaction with the active sites. Those dispersed in the amorphous carbon with porous morphology form larger sized droplets by collision and coalescence of the smaller sized droplets.