Vaporization of indium nitrate in the graphite tube atomizer in the presence of chemical modifiers

Abstract

The CCD spectrometer coupled with the graphite tube furnace was employed to investigate the vaporization of micrograms of In (as nitrate). Fifty absorption spectra between 200 and 475 nm were collected during 10 s while the tube temperature increased from 700 to 2600–2700 K. The vaporization was carried out in the pyrocoated, Ir-sputtered and Ta-lined tubes in the presence of Cu, Co, Ni, Pd and Mg nitrates, sodium tungstate, ascorbic acid and ammonium hexachloroiridate monohydrate after thermal pretreatment. In the pyrocoated tube the vaporization of In occurred at 1350–1550 K with fast evolution of molecular vapor. The observed broad bands with maxima at 225, 290 and 275 nm were attributed to In 2O and InO, according to their thermal behavior. Cu, Co, Ni, Pd, Ir modifiers, Ta-lining and Ir sputtered surface suppressed the release of In oxides and induced the delayed appearance of In atomic lines simultaneous with a broad band at 205 nm, tentatively attributed to In dimer. Tungsten caused faster and more complete reduction of In oxide than carbon. Indium oxide bands were substituted between 1100 and 1350 K by a band at 244 nm assigned to gaseous tungsten oxide. Ascorbic acid caused the decrease of indium oxide fraction in gas phase. The presence of MgO in the tube led to the decrease of the band at 205 nm. The vaporization of micrograms of Cu, Co, Ni, Pd and MgO in the pyrocoated tube caused the appearance of absorption and emission continuum, superimposed to In atomic lines at temperatures above 1550 K. This effect had been earlier explained as induced by exothermal interaction of the vaporized substance with carbon. SEM observations of Ir deposits on the graphite surface confirmed the interaction of Pt group metals with carbon at high temperature. A similar effect is advanced for other metal modifiers.