DISCRIMINATION BETWEEN ADSORPTION AND COPRECIPITATION IN AQUATIC PARTICLE STANDARDS BY SURFACE-ANALYSIS TECHNIQUES - LEAD DISTRIBUTIONS IN CALCIUM CARBONATES

Standard calcium carbonate (calcite) particles were generated to contain either coprecipitated or adsorbed lead. Conventional analytical techniques (atomic spectroscopy, X-ray diffraction, X-ray microanalysis, electron microscopy) fail to distinguish the two particle types. However, distinguishing between particle surface and interior compositions is possible with surface analytical techniques, notably secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS). This permits the discrimination of surface adsorbed from coprecipitated lead in particles with similar average (bulk) concentrations.