Analyte stabilization by electrodeposited palladium modifier for electrothermal atomic absorption spectrometry: characterization by scanning electron microscopy and anodic stripping voltammetry

In electrothermal atomic absorption spectroscopy (ETAAS) effective stabilization of analytes can be achieved by an initial in situ electrodeposition of 0.2 mug of Pd. This amount of Pd is on average a factor of 50 lower than that typically used for conventional chemical modification. The surface features of this modifier have been characterized by scanning electron microscopy (SEM) measurements on sectioned pyrolytic graphite furnaces and contrasted with those for modifier produced from thermally reduced Pd salts. Electrodeposition produces a uniform array of Pd domains stretching approximately 2 mm from the centrally positioned Pt/Ir anode (which doubles as the autosampler sample delivery tube). In contrast, thermally reduced Pd salts produce a modifier which concentrates in domains near the drying edge of the modifier solution. Anodic stripping voltammetry (ASV) established that Pb electrodeposited onto Pd-modified pyrolytic graphite affixes to the Pd rather than the graphite. ASV measurements using a basal plane pyrolytic graphite working electrode also established that (i) the stripping potentials for monolayer and multilayer Pb are shifted anodically by 0.16 and 0.18 V, respectively by binding to Pd rather than graphite and (ii) deposition of Pb from dilute acidic medium (1% HNO(3)) leads only to monolayer Pb, in contrast to deposition from acetate buffer (pH 4.0-4.4) which produces predominantly multilayer Pb.