EFFECT OF ASCORBIC-ACID ON THE DESORPTION OF GOLD IN GRAPHITE-FURNACE ATOMIC-ABSORPTION SPECTROMETRY

In the graphite furnace atomic absorption spectrometry of gold, signals with a single peak were observed with a pyrolytic graphite (PG) furnace, while signals with a shoulder on the tailing edge were observed with a nonpyrolytic graphite (NPG) furnace. A thermal shift of the atomic absorption signals for gold occurs in response to changes in the concentration of ascorbic acid without any loss for each furnace. When the pre-pyrolysis of a 5% (m/V) ascorbic acid solution was carried out at 1270 K, although the background signal due to the release of amorphous carbon was not observed, a thermal shift of the gold signal was confirmed. At a pre-pyrolysis temperature over 1460 K, the peak absorbance was reduced by increasing the pre-pyrolysis temperature, while absorbance at the position of the signal for gold only was increased. The values of the Arrhenius activation energy for the desorption of gold were obtained to be 60 +/- 2 kcal mol-1 for gold only, 93 +/- 3 kcal mol-1 for gold with 5% (m/V) ascorbic acid and 99 +/- 2 kcal mol-1 after a pre-pyrolysis of ascorbic acid at 1270 K.