Simple nitric acid dissolution method for electrothermal atomic absorption spectrometric analysis of atmospheric aerosol samples collected by a berner-type low-pressure impactor

Abstract

The aim of this study was to develop a simple dissolution method for atmospheric aerosol samples collected using a Berner impactor. Particular care was taken to ensure that the procedural blank contributions were as low as possible for the elements investigated. The impactor samples were treated for two or three 20 min periods with 0.2 mol l^–1 nitric acid in polystyrene test-tubes in an ultrasonic bath at 50 °C. Electrothermal atomic absorption spectrometry (ETAAS) with a graphite furnace was used to determine 14 elements: Al, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, V and Zn. With the exception of Zn, for which a platform was used, all analytes were atomized off the wall of the graphite tube. The blank values for Al, Cd, Cu, Mn, Ni, Pb and V were found to be at or below the detection limits of the method. The blank values for Ca, Fe, K, Mg, Na and Zn varied between 0.5 and 3 µg l^–1 but Cr showed an unsuitably high blank of 8 µg l^–1. The dissolution method was tested on the National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 1648 Urban Particulate and the recoveries were found to be 80–93% for Pb, Zn, Cd and Cu. The least recoverable elements in this matrix were Al, Cr, Fe, K and Na, with recoveries between 20 and 44%. A prolonged dissolution time had only a minor effect on the recoveries. Additional tests involved the analysis of ambient aerosol samples, collected with a cascade impactor, by both ETAAS and instrumental neutron activation analysis (INAA), with the latter technique providing the reference values. Six elements (Al, Cu, Mg, Mn, Na and V) were measured by both techniques. Compared with the NIST material, the fine particle (equivalent aerodynamic cut-off diameter<2 µm) impactor samples clearly showed better recoveries for Cu (91%), Mn (90%), Na (102%) and V (96%). Similar or even better recoveries are also expected for fine particle Cd, Zn and Pb, which were not measured in our INAA procedure but exhibited the highest recoveries for the NIST material. For Al, on the other hand, the results from the impactor samples were similar to those for the NIST material and there was a trend that the recoveries were decreasing with increasing particle size, because of incomplete dissolution of the soil dust particles and a lower ability of the coarser particles to form a suspension. Moreover, coarse particle Al was recovered mostly as particulate material. It is assumed that our dissolution method is valid for measuring fine particle Cd, Cu, Mg, Mn, Na, Pb, V and Zn in ambient aerosol samples collected on polycarbonate film by various types of impactors.