IDENTIFICATION OF NITRATES AND SULFATES WITH DYNAMIC SIMS

Sputter conditions are outlined for the identification of chemically sensitive salt compounds, such as nitrates or sulphates, in multicomponent samples of environmental origin using dynamic SIMS for depth-profiling with nanoscale resolution. Sputtering with 1 keV Xe+ has been found to be appropriate to enable both the emission of decisive molecular ions with enough intensity as well as substantial erosion for depth-profiling. The use of heavy projectiles reduces the destruction of chemical compounds in the surface of the solid and enhances sensitivity and identification power of SIMS. The method was applied to the analysis of urban outdoor aerosol particles to investigate the conversion of NaCl into Na(2)S0(4) or NaNO3, by the interaction of sea salt aerosol with the atmospheric pollutants NOx and SOx. Only NaNO3 was found in the sea salt fraction.