Solid sampling approaches for quantitative analysis of trace elements in powdered environmental samples using ICP-based measurement techniques

Abstract

Accurate quantification of trace elements in environmental samples such as fly ash, sewage sludge, road dust or airborne particulate matter is important for assessment of health effects but also to estimate their potential for recycling. To obtain such information in a routinely way ICP-OES or ICP-MS is applied for analysis. When using these techniques in their regular configuration, conversion of the solid material into a liquid solution is necessary. For this purpose, well established procedures such as acid digestion, fusion or dry ashing are reported in literature. However, application of these approaches is limited by the enhanced risk for sample contamination and/or analyte losses, as well as the increased time demand for sample preparation. Therefore, the direct analysis of the mentioned solid samples is considered to be advantageous. Solid-sampling techniques which are frequently applied in combination with ICP-OES or ICP-MS detection are electro-thermal-vaporization (ETV) and laser-ablation (LA). However, the need of appropriate matrix matched standards or certified reference materials (CRM) for quantitative determinations limits the applicability of the abovementioned techniques. In this work, different approaches for the direct analysis of environmental powders have been developed, which require no or only little sample preparation. The proposed LA-ICP-MS and ETV-ICP-OES procedures were carefully optimized to overcome frequently observed limitations and validated for future routine means. Environmental powders like fly-ash and sewage sludge were chosen as sample material for method development but also for demonstration of applicability. In the first part of the work improved procedures for analysis of powdered samples were presented, which allow the determination of minor and major sample constituents without the need of certified reference materials closely matching the samples matrix composition. In case of LA-ICP-MS this goal could be achieved with the use of in-house standard materials prepared by pelletizing mixtures of available non-matrix-matched reference materials with binder compounds in the presence of an internal standard. Fast and reliable ETV-ICP-OES analysis of overall bulk concentrations has been enabled using a slurry approach, where the powdered sample is dispersed in a liquid without dissolving them, offering the possibility of external calibration with aqueous standard solutions. The second part of this thesis was focused on the spatially resolved LA-ICP-MS analysis of isolated fly ash particles. Thereby, information about the lateral distribution of various elements present in fly ash particles could be obtained, enabling a more detailed characterization of the particles. For example, elements enriched on the particles surface could be more easily mobilized into the environment than elements predominantly occurring in the particles core. The recycling of precious metals from environmental powders is also favored in case of surface enriched elements as well as the potential release of toxic elements into the environment.