Role of iron modifier on boron atomization process using graphite furnace-atomic absorption spectrometry based on speciation of iron using X-ray absorption fine structure

Abstract

The role of an Fe modifier on boron atomization process using graphite furnace-atomic absorbance spectrometry was investigated using a spectroscopic approach. The initial state of the Fe modifier in a pyrolytic graphite (PG) furnace was trivalent. With an increase in pyrolysis temperature, the Fe modifier was reduced in a stepwise manner. Fe2O3 and Fe3O4 were dominant at pyrolysis temperatures below 1300K. From 1300 to 1500K, FeO was dominant. At temperatures higher than 1700K, Fe metal was dominant. After a drying step, 17.7% of the initial B remained in the PG furnace. After the pyrolysis step at 773K, the residual fraction of B was similar to that after the drying step. After the pyrolysis step at a temperature of 1073K, the residual fraction was 11.7%. At pyrolysis temperatures>1738K, the residual fraction was <3.3% (<limit of detection). In the absence of the Fe modifier, B was not detected, even after the drying step. The Fe modifier acted as an adsorbent and retentive agent for B in the PG furnace during the drying and pyrolysis steps. Our results showed that improvement of B absorbance in the presence of the Fe modifier was owing to B retention by Fe oxide with a high oxidation number. The variation of B absorbance with increasing pyrolysis temperature could be explained by differences in the B retention capacity of Fe species in the PG furnace.