EFFECT OF THE SURFACE-TREATMENT OF A GRAPHITE-FURNACE WITH A REFRACTORY ELEMENT (HAFNIUM, TITANIUM, TUNGSTEN AND ZIRCONIUM) BY A ONE-DROP COATING METHOD ON THE ATOMIZATION MECHANISM OF INDIUM IN ELECTROTHERMALATOMIC-ABSORPTION SPECTROMETRY

In the present work we investigated the atomization mechanisms of indi um in electrothermal atomic absorption spectrometry with pyrolytically coated graphite (PG) and non-pyrolytically coated graphite (NPG) furn aces treated with a refractory element, such as Hf, Ti, W or Zr, by a one-drop coating method. A single-peak signal was observed in Hf-, Ti- and Zr-treated PG and NPG furnaces, and an unresolved double peak sig nal was observed in W-treated PG and NPG furnaces. The effects of the surface treatment on the charring curve (charring temperature-absorban ce curve), kinetic data and Raman spectroscopic data were investigated . The charring curve was shifted to a high-temperature side with a gre at sensitivity enhancement after the surface was treated, correspondin g to suppression of the sensitivity loss reaction of In (In2O3(s)+2C(s )-->In2O(g)+2CO(g)). The Arrhenius activation energy (E-a) was estimat ed to be 158+/-10, 146+/-10 and 145+/-10 kJ mol(-1) and 170+/-15, 194/-15 and 165+/10 kJ mol(-1) with Hf-, Ti- and Zr-treated PG and NPG fu rnaces, 180+/-15 kJ mol(-1) for the first peak with W-treated NPG one, 115+/-10 and 111+/-10 kJ mol(-1) for the second peak with W-treated P G and NPG ones, respectively. The Raman spectra of the treated graphit e surface were measured at various sites in the sample compartment. Th e ratio of the intensity of the D band (disordered mode) to that of th e G band (E-2g mode), I-D/I-G, was increased by a surface treatment. T his suggests an increase in the number of disordered sites, such as ed ge carbon atoms and the boundaries of graphite crystallites, which exi st in uncoated regions of graphite within the treated area. Arrhenius activation energy, except for the second peak with the W-treatment, de creased along with an increase in I-D/I-G when using a treated furnace . From this relationship, it was proposed that the atomization of indi um in treated furnaces takes place due to collisions between In2O(g) a nd the uncoated region of graphite. When using a W-treated furnace, di ssociation of the indium dimer was attributed to a rate-determining st ep for the second peak.