Iridium and rhodium as permanent chemical modifiers for the determination of Ag, As, Bi, Cd, and Sb by electrothermal atomic absorption spectrometry

Performance of graphite platforms coated with Ir, Rh, and a mixture of both , as permanent modifiers for Ag, As, Bi, Cd, and Sb, was evaluated. The coa ting process is very simple: a solution containing Ir, Rh. or a mixture of both is pipetted on the platform inserted in a graphite tube, and this is s ubmitted to a temperature program. High pyrolysis temperatures are allowed, especially for As and Bi, 1400 degrees C, in the Ir + Rh-coated platform. The sensitivity remains about the same for all analytes with different coat ings, except for As in the Ir-coated platform. for which a remarkable gain was obtained in comparison to the other coatings. The lifetimes of the trea ted tubes were in the range 50 to more than 1000 cycles, being especially l ong for Sb and Ag in the Rh-coated platform, more than 600 and 1000 cycles, respectively. The Rh coating could not be used for Bi and Cd. Analysis of a certified reference water and of acid oyster tissue digests showed the ab sence of interference and good precision. Advantages of the permanent coati ngs are the possibility of low blanks by in situ cleaning of the modifier a nd shorter analysis time. (C) 1998 Academic Press.