IDENTIFICATION OF NITRATES AND SULFATES WITH DYNAMIC SIMS

Sputter conditions are outlined for the identification of chemically s ensitive salt compounds, such as nitrates or sulphates, in multicompon ent samples of environmental origin using dynamic SIMS for depth-profi ling with nanoscale resolution. Sputtering with 1 keV Xe+ has been fou nd to be appropriate to enable both the emission of decisive molecular ions with enough intensity as well as substantial erosion for depth-p rofiling. The use of heavy projectiles reduces the destruction of chem ical compounds in the surface of the solid and enhances sensitivity an d identification power of SIMS. The method was applied to the analysis of urban outdoor aerosol particles to investigate the conversion of N aCl into Na(2)S0(4) or NaNO3, by the interaction of sea salt aerosol w ith the atmospheric pollutants NOx and SOx. Only NaNO3 was found in th e sea salt fraction.