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

The CCD spectrometer coupled with the graphite tube furnace was employed to investigate the vaporization of micrograms of In (as nitrate). Fifty absor ption spectra between 200 and 475 nm were collected during 10 a while the t ube temperature increased from 700 to 2600-2700 K. The vaporization was car ried 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 amm onium hexachloroiridate monohydrate after thermal pretreatment. In the pyro coated tube the vaporization of In occurred at 1350-1550 K with fast evolut ion of molecular vapor. The observed broad bands with maxima at 225, 290 an d 275 nm were attributed to In2O and InO, according to their thermal behavi or. Cu, Co, Ni, Pd, Ir modifiers, Ta-lining and Ir sputtered surface suppre ssed the release of In oxides and induced the delayed appearance of In atom ic lines simultaneous with a broad band at 205 nm, tentatively attributed t o 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 mic rograms of Cu, Co, Ni, Pd and MgO in the pyrocoated tube caused the appeara nce of absorption and emission continuum, superimposed to In atomic lines a t temperatures above 1550 K. This effect had been earlier explained as indu ced by exothermal interaction of the vaporized substance with carbon. SEM o bservations of Ir deposits on the graphite surface confirmed the interactio n of Pt group metals with carbon at high temperature. A similar effect is a dvanced for other metal modifiers. (C) 2001 Elsevier Science B.V. All right s reserved.