| Popis: |
A procedure for the determination of cadmium, chromium, and lead in marine sediment slurries by electrothermal atomic absorption spectrometry is proposed. Slurry was prepared by mixing 10mg of ground sample with particle size smaller than 50 microm completed to the weight of 1.0 g with a 3% nitric acid and 10% hydrogen peroxide solution. The slurry was maintained homogeneous with an aquarium air pump. For cadmium, the best results were obtained using iridium permanent with optimum pyrolysis and atomization temperatures of 400 and 1300 degrees C, respectively, a characteristic mass, m(o) (1% absorption), of 2.3 pg (recommended 1 pg). Without modifier use, zirconium, ruthenium, and rhodium m(o) were 3.4, 4.1, 4.6, and 4.8 pg, respectively. For chromium, the most sensitive condition was obtained with zirconium permanent with optimum pyrolysis and atomization temperatures of 1500 and 2500 degrees C, m(o) of 6.6 pg (recommended 5.5 pg); and without modifier use, rhodium, iridium, and ruthenium m(o) were 5.3, 8.8, 8.8, and 8.9 pg, respectively. For lead, the best modifier was also zirconium, m(o) of 8.3 pg for the optimum pyrolysis and atomization temperatures of 600 and 1400 degrees C, respectively, (recommended m(o) of 9.0 pg). For iridium, ruthenium, without modifier, and rhodium, m(o) were 14.7, 15.5, 16.5, and 16.5 pg, respectively. For all the modifiers selected in each case, the peaks were symmetrical with r(2) higher than 0.99. Being analyzed (n=10), two marine sediment reference materials (PACS-2 and MESS-2 from NRCC), the determined values, microg l(-1), and certified values in brackets, were 2.17+/-0.05 (2.11+/-0.15) and 0.25+/-0.03 (0.24+/-0.01) for cadmium in PACS-2 and MESS-2, respectively. For chromium in PACS-2 and MESS-2 the values were 94.7+/-5.6 (90.7+/-4.6) and 102.3+/-10.7 (106+/-8), respectively. Finally, for lead in PACS-2 and MESS-2, the results obtained were 184+/-7 (183+/-8) and of 25.2+/-0.40 (21.9+/-1.2), respectively. For cadmium and lead in both samples and chromium in PACS-2, calibration was accomplished with aqueous calibration curves. For chromium in MESS-2, only with the standard addition technique results were in agreement with the certified ones. The limits of detection (k=3, n=10) obtained with the diluents were 0.1, 3.4, and 3.6 microg l(-1) for cadmium, chromium, and lead, respectively. |
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