THE COUPLED SdFFF-CID-ETAAS APPROACH FOR DIMENSIONAL AND ELEMENTAL CHARACTERIZATION OF ENVIRONMENTAL COLLOIDS

The characterization of environmental colloids is an important topic since they play an important role in performing pollutant transport (i.e. in aquatic systems or in the atmosphere) or enhancing their accumulation (i.e. in soils), depending upon the degree of their mobility. Size and elemental characterization of this colloidal material requires a preliminary separation step, in order to obtain relatively monodisperse fractions to present to the detection system for the chemical characterization. By using Field-Flow Fractionation (FFF) methods, different size fractions can be collected (across the sample size distribution) for subsequent investigation, as for example, heavy metal load determination1. In particular, Sedimentation Field-Flow Fractionation (SdFFF) technique, already applied to environmental colloids, is an established method for the high resolution, mass based separation and sizing of colloids in the 0.05 – 1.0 m size range2. Some limiting factors of this technique are the small amount of the sample that can be processed in a single FFF separation run and the dilution of collected fractions. These limitations means that only a very sensitive analytical method can be used to characterize the separated particle fraction, or time-consuming concentration steps are required, with the consequence of a further sample handling procedure. In the present work Electrothermal Atomic Absorption Spectrometry (EAAS) is applied as on-line detection system for SdFFF. The coupling is performed through a pre-concentration device - Capillary Injection Device (CID) - which allows the direct introduction of the analytical solution into the graphite furnace to an extent of some ten milliliters, providing an in-situ preconcentration3. The hyphenated approach which allows to determine trace elements on different size range colloidal fractions, is evaluated with respect some standard particle samples of known size distribution