Determination of ultra-trace levels of palladium in environmental samples by graphite furnace atomic spectrometry techniques

Abstract

Palladium, one of the platinum group elements (PGEs), has received an increasing attention during the past 15 years by manufacturers of automotive catalytic converters (ACCs) (Johnson Matthey, 2004). Pd-rich ACC units exhibit a more efficient elimination of harmful and/or toxic components of exhaust gases (e.g., CO, NOx, and hydrocarbons) originating from diesel- and petrol-fuelled vehicles and some household utensils. Moreover, due to the advantage of Pd catalysts at lower working temperatures, they are successful in decreasing the level of exhaust fumes at cold starts of engines. Thus, cars equipped with these novel ACC units can meet even stricter emission limits for petrol-fuelled vehicles. On the other hand, the concentration of anthropogenically evolved PGEs, including Pd, has been continuously increasing in the environment since the introduction of ACCs (Zereini and Alt, 2000; Ravindra et al., 2004). Anthropogenic Pd has been reported to be mobile and bio-accumulated by aquatic organisms, generally, to a larger extent than Pt and Rh (Sures et al., 2001, 2002a; 2002b). Moreover, metallic Pd has an allergenic potential on humans (Van Ketel and Niebber, 1981). Therefore, the monitoring of the level of Pd in various environmental compartments and biological matrices appears to be an important task in order to assess the risk of this element to human health and the environment. Graphite furnace atomic absorption spectrometry (GFAAS) is a selective, and sensitive analytical technique, thus, it has been widely applied to the determination of Pd in a large variety of environmental/biological matrices (Bencs et al., 2003). In environmental compartments and biological matrices, however, the concentrations of PGEs are fairly low (pg g-1 ng g-1 level), which often requires the application of pre-concentration/ matrix separation steps prior to their GFAAS detection (Bencs et al., 2003; Godlewska-ykiewicz, 2004). The low level of Pd is also true for almost all the matrices exposed to a major anthropogenic emission source of PGEs, e.g., heavy traffic sites (Zereini and Alt, 2000; Ravindra et al., 2004). Electrothermal vaporization (ETV) sample introduction methods comprise the vaporization of samples from a graphite/metal sample holder inserted within a resistance heated graphite furnace and subsequent transport of the evolved sample vapours to the detection source. Therefore, ETV studies also supply with very important data on the vaporization behaviour of analytes/matrices, and thus the literature generally refers to ETV as a complementary technique to GFAAS. This consideration is also a motivation for incorporating the ETV-related studies on Pd together with GFAAS into the present study.