Characterization of colloidal particles by laser-induced plasma spectroscopy (LIPS)

To study the nature and abundance of colloids in aquifer systems Laser-Induced Plasma Spectroscopy (LIPS) was used for elemental analysis of heavy metal colloids with particle diameters between 0.1 and 1 μm. Different experimental approaches to the qualitative and quantitative characterization of inorganic colloids are examined. Some of the inherent problems associated with a direct detection are discussed. A direct detection of colloids in water or a liquid jet without separation between solvent and particles yielded only inadequate spectral resolution and detection limits in the order of mg l−1. Utilization of a miniaturized ultrafiltration system with a 0.1 μm membrane filter gave absolute limits of detection in the ng-range with good reproducibility. Figures of merit are given for representative heavy metal colloids. The filtration device used in this work is suitable for subsurface sampling under flow conditions, which minimizes sampling artifacts. A slightly modified LIPS system will be used for field screening and monitoring.