Discrimination between adsorption and coprecipitation in aquatic particle standards by surface analysis techniques: lead distributions in calcium carbonates

Techniques for distinguishing between particles with trace elements uniformly distributed in the particle bulk from those with surface enrichment were evaluated using standard particles of calcium carbonate with similar bulk concentrations of adsorbed or coprecipitated lead. Significantly different lead distributions for the adsorbed and coprecipitated samples were obtained using a secondary-ion mass spectrometry technique, and the results were not affected by coprecipitate ageing times greater than 15 minutes. The extent of lead surface enrichment was determined by X-ray photoelectron spectroscopy which complemented the secondary-ion mass spectroscopic data. The two particle types were not distinguished by bulk and microscopic analysis by atomic spectroscopy, X-ray diffraction, X-ray microanalysis or electron microscopy.