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 mu m.
Different experimental approaches to the qualitative and quantitative
characterization of inorganic colloids are examined. Some of the inher
ent problems associated with a direct detection are discussed. A direc
t detection of colloids in water or a liquid jet without separation be
tween solvent and particles yielded only inadequate spectral resolutio
n and detection limits in the order of mg l(-1) Utilization of a minia
turized ultrafiltration system with a 0.1 mu m membrane filter gave ab
solute limits of detection in the ng-range with good reproducibility.
Figures of merit are given for representative heavy metal colloids. Th
e filtration device used in this work is suitable for subsurface sampl
ing under flow conditions, which minimizes sampling artifacts. A sligh
tly modified LIPS system will be used for field screening and monitori
ng.