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 coating 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 submitted 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 coatings, 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 treated tubes were in the range 50 to more than 1000 cycles, being especially long 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 absence of interference and good precision. Advantages of the permanent coatings are the possibility of low blanks by in situ cleaning of the modifier and shorter analysis time. (C) 1998 Academic Press.