Surface and subsurface examination of graphite tubes after electrodeposition of noble metals for electrothermal atomic absorption spectrometry

The modification phenomena of noble metals (Pd, Ir, Rh) electrodeposited on to the inner surface of pyrolytic graphite (PG) coated furnaces were invest igated mainly by electron microprobe analysis with energy dispersive X-ray emission detection. The conditions of electrodeposition were optimized in o rder to achieve the best analytical performance of atomic absorption measur ements. Investigations concerning the distribution of noble metals on the t ube surface and in-depth were performed at different stages of the tube his tory. It was found that the noble metals used for the modification do not f orm a compact layer on the surface but penetrate into the pyrolytic graphit e structure already at the deposition step. When two metals were deposited together, both penetrated into the graphite structure. The degree of penetr ation of the pyrolytic graphite at high temperature differs for various met als. It was also demonstrated that electrodeposited noble metals remain in sub-surface domains of the graphite for hundreds of atomization cycles, whi ch means that they can be used as permanent modifiers. (C) 2001 Elsevier Sc ience B.V. All rights reserved.