ULTRATRACE DETERMINATION OF CADMIUM BY ATOMIC-ABSORPTION SPECTROMETRYUSING HYDRIDE GENERATION WITH IN-SITU PRECONCENTRATION IN A PALLADIUM-COATED GRAPHITE ATOMIZER

A very sensitive ETAAS method, with in situ trapping of the metal, is described for ultratrace determinations of Cd in liquid solutions. It is based on volatile Cd HG from a vesicular solution with subsequent t rapping of the metal in a graphite platform coated with Pd. This Pd co ating, on a pyrolytic graphite L'vov platform, acts as the atomizer, S odium tetrahydroborate(nr) in a vesicular medium of didodecyldimethyla mmonium bromide is used to generate Cd hydride from the sample solutio n, This volatile species is trapped by the Pd coating, pre-heated at 1 50 degrees C, the preconcentrated Cd then atomized at 1600 degrees C a nd the transient AAS signal measured, Detection limits (DL) observed a re in the ng l(-1) range (e.g., using a 1.4 ml Cd sample volume for pr econcentration the DL was 60 ng l(-1)). Higher preconcentrations up to a maximum of 1.4 ng of total Cd deposited are possible with the propo sed methodology, The RSD for ten replicate analyses of 1.4 mi of 500 n g l(-1) Cd solution (0.7 ng of total Cd) was 1.7%. The combination of vesicles-mediated HG with the ease of decomposition of Cd hydride on t he Pd coating at 150 degrees C, provides a convenient Cd preconcentrat ion method for enhancing the sensitivity of direct determinations of C d by conventional ETAAS or by HGAAS.