Preconcentration and separation methods for the determination of trace palladium in environmental samples

Abstract

Palladium is an element of increasing importance in todays industries. Due to the catalytic properties it is widely used in the synthesis of many materials, from polymers to pharmaceuticals. In addition to this, its emission from the automotive catalytic converters has resulted in an increase in the concentration of palladium in the environment. An elevated level of Pd compared to geochemical background (Helmers et al. 1998) has been found in airborne particulate matter (Tilch et al. 2000), road dust (Boch et al. 2002; Kovacheva and Djingova 2002; Leniewska et al. 2004), soil (Patel et al. 2000; Ravindra et al. 2004) and grass (Schuster et al. 1999). Van de Velde et al. (2000) presented comprehensive data on the occurrence of Pd in alpine ice and snow dating from the late 18th century to the early 1990s. Increasing palladium content in the samples collected at a high-altitude location near the summit of Mont Blanc was detected, particularly over the last decade. The monitoring of Pd in environmental samples has great importance with respect to estimation of the future risk of the human health and the ecosystem. Palladium analysis requires analytical methods of high sensitivity, selectivity and the control of interference effects. The most widely used methods for determination of Pd in environmental samples include graphite furnace atomic absorption spectrometry (GFAAS), inductively coupled plasma mass spectrometry (ICP-MS) and adsorptive stripping voltammetry (ASV). Despite the high sensitivity, ICP-MS requires appropriate choice of sample introduction technique, preferably one possessing the option of solid sample introduction (Kntor, 2001). Moreover, spectral and non-spectral interferences could cause several difficulties in the correct determination. Riepe et al. (2001) proposed chemically modified sample introduction capillary to remove the interfering elements for the determination of Pd by ICP-MS. The strong cation-exchanger (2-(4-chlorosulfonylphenyl)- ethyltrichlorosilane), covalently bound to the silica capillary, can retain Cu2+ and YO+ during sample introduction, whereas palladium breaks through the capillary and can be determined in the absence of interfering matrix constituents. Other sensitive techniques such as neutron activation analysis (NAA) or total reflection X-ray fluorescence spectrometry (TXRF) are less often applied due to the complexity and cost of the required instrumentation. It should be remarked that for palladium determination by NAAA detection capability is limited due to strong interference of bromide, mainly 82Br, which is present in almost all organic matrices in the ultra trace range (Schwarzer et al. 2000). The analytical methods for the determination of palladium as well as other platinum group elements have been recently reviewed (Rao and Reddi, 2000; Bencs et al. 2003; Barefoot, 2004) In environmental samples, the low concentration of palladium (nanogram per gram levels) together with the high concentration of interfering matrix components often requires an enrichment step combined with a matrix separation. Fire-assay, coprecipitation, solvent and solid phase extraction techniques have been developed and applied for preconcentration and separation of palladium prior its detection. An alternative approach may be based on the electrodeposition to avoid matrix interferences. The selection of a suitable enrichment procedure depends considerably on the palladium concentration and the method for its final determination. The preconcentration procedures are executed for off- or on-line systems. Application of off-line enrichment is adequate when higher preconcentration factors are needed. However, these procedures require a great amounts of reagent and samples. When on-line systems are condidered, the main advantage is the possibility of automation which increases precision and accuracy. Further, it reduces the risks of sample contamination. Detailed information reffering to on-line preconcentration systems coupled to atomic spectrometry can be obtained from the literature (Burguera and Burguera, 2001; Alonso et al. 2001).