ROLE OF METAL-MATRIX MODIFIER IN ASHING AND BEGINNING OF THE ATOMIZATION PROCESS IN GRAPHITE FURNACE-ATOMIC ABSORPTION SPECTROMETRY

It has been shown that Pb, Sn and In form alloys with the Pd matrix mo difier during the ashing and the beginning of the atomization process in graphite furnace atomic absorption spectrometry. Pb and Sn were cho sen as analytes and Ag, Sb, Cu, Au, Pt, Pd, Cd, and Mg as co-existing elements or matrix modifiers. The activity coefficients of Pb in the a lloys Pb-Ag and Pb-Sb are similar to the value of Pb alone (or about 1 .0), and those in the alloys Pb-Au, Pb-Pt and Pb-Mg are lower than the value of 1.0; in particular the activity coefficients of Sn in the al loy Sn-Pd is extremely low. The activity coefficients of Pb in the all oys Pb-Cd and Pb-Cu are higher than 1.0. The movement of volatilizatio n to higher effective temperatures in the atomization were studied; it was found that: 1) Where the activity coefficient of the analyte was lower than 1.0, intermetallic compounds were formed and the atomizatio n shifted to higher temperatures. 2) Atomization was not altered (even though the activity coefficients were different from 1.0) if the modi fier elements formed alloys with Pb, which had melting temperatures lo wer than the ashing and the initial temperatures of the atomization of Pb. 3) For metals such as Mg, which are neither reduced to metal nor form alloys with the analyte during the ashing and the atomization pro cess, the role as matrix modifier is different, as has also been studi ed herein.