Determinação de elementos -traço Pb e Zn em rochas graníticas por espectrofotometria de absorção atómica com atomização por Chama

Abstract

The present work intends to show the possibility of determination of pb and Zn in 6 samples of granitic rocks by flame atomization atomic absorption spectrophotometry ("FAAS"). The samples and the reference material were dissolved with acid mixture, H2O-HNO3-HCIO4 in the ratio (0.5:1:2). The accuracy of the method was checked by analysing the reference materials, GA and GH, granites supplied by the "USGS" (United States Geological Survey), of the United States of America. According to statisticians the results obtained and those recommended from the reference materials were concordant. The relative error values (Er) of determination of these elements were 8.2% and 4.0% for Pb and 2.4 and 1.2 for Zn, respectively, in the GA and GH reference materials. The Pb and Zn values obtained by "FAAS" (Flame Atomic Absorption Spectrophotometry) and "ICP-MS" (Inductively Coupled Plasma-Mass Spectrometry) methods were compared. Through the linear regression method it was found that the results obtained in both methods are concordant at a 95% confidence level. The accuracy in Zn determination was very good with the percentage relative standard deviation("%RSD") ranging from 0.27 to 0.74, 0.37 to 0.57 and 0.15 to 1.09, respectively, in the reference materials GA, GH and samples. In the determination of Pb the precision was very good for the reference materials GA and GH, with the %RSD ranging from 1.20 to 2.61 and from 1.21 to 1.94, respectively. It was very good for 6 samples and good for the remaining with %RSD values ranging from 1.76 to 8.51. (TRADUÇAO NOSSA)