Extraction et analyse des éléments majeurs et traces contenus dans les poussières prélevées dans l’air ambiant à Constantine .

Abstract

When high mineral loads in atmospheric particulate matter (PM) are present, particular attention should be paid to the selection of appropriate acidic digestion protocols for wet chemical analysis. We report on a comparative study of elemental recovery yields from five different pre-analytical acid digestion procedures for mineral-rich urban background PM10 samples collected in the city of Constantine (Northeastern Algeria). Five reference materials (NIST 1633b, UPM 1648, NAT-7, SO-2 and SO-4) were also digested according to the same protocols. The selected acidic digestion procedures are widely used for PM chemical analysis, and comprise: P1 (HNO3/HF/HCl), P2 (HCl/HNO3), P3 (HCl/H2O2/HNO3), P4 (HNO3/HF/HClO4) and P5 (HNO3/H2O2); the latter is assisted with micro-wave digestion. Elemental recovery yields were compared for major and trace elements typically determined in PM for source apportionment analysis and the results evidenced large differences. For most elements, the bulk extraction procedures (requiring the use of HF) allowed a full elemental recovery, particularly for elements that are associated with aluminum-silicate species and oxides that are resistant to mild acid attack. In contrast, in the extraction protocols without HF, low recovery yields were obtained for elements such as Al, Ti, Zr, Sc, and other aluminumsilicate-related elements in PM10 samples with high mineral dust load. We highlight that the European standard digestion method EN-14902: 2005 should be applied specifically for the metals for which this method was developed, but caution should be taken when the analysis of other elements in PM is required, especially in urban areas where road and vehicle wear dust is likely to be a major component of ambient PM. When using wet chemistry analysis for PM source apportionment studies, we strongly recommend HF bulk dissolution of samples to ensure the reliability of the geochemical information when coupled with an appropriate analytical tool.