Abstract The application of laser-induced breakdown detection (LIBD) as a new and powerful particle-analyz- ing technique for the determination of solubility data by monitoring initial colloid generation, when the metal ion concentration just exceeds the solubility at a given pH value, is investigated. Laser-induced breakdown spec- troscopy (LIBS) is used for selective analysis of an aque- ous suspension of lanthanide oxide particles in the pres- ence of the respective lanthanide aquo ion. The detection limit for aquo ion and oxide particle is determined. On the basis of the different detection limits, the LIBS technique is used to study the formation of hydroxide colloids in aqueous solution by varying the pH value until the solu- bility limit is exceeded. LIBS enables both qualitative and quantitative monitoring of particle formation without arti- facts arising from other contaminants. LIBD and LIBS are described and compared. The advantages and disadvan- tages of the methods for the determination of solubility data are discussed. Introduction The influence of colloids on the migration of pollutants such as heavy metals or toxicologically relevant organics is an important topic in environmental related research of aquatic systems. Colloids are present in all aquatic sys- tems [1], they are between 10 –9 and 10 –6 m in diameter [2] and therefore have a high specific surface to mass ratio. As a consequence colloids have a high capacity for sorp- tion of pollutants and may facilitate their transport [3, 4]. Sorption processes of contaminants on colloid surfaces are of vital importance for prediction of the migration be- havior of hazardous substances. Formation of colloidal species from toxic substances, e.g. heavy metals, in- creases their stability beyond their thermodynamic solu- bility [5]. Therefore both the number density and the size distribution of colloids in environmentally relevant low concentrations, as well as the elemental composition of these nano particles are essential information. Also, for the prediction of solubility data the detection of colloids in the lower part of the nanometer range is of fundamen- tal importance. For quantification of very small colloid particles in the ng L –1 concentration range laser-induced breakdown de- tection (LIBD) is a very powerful technique [6, 7]. It is based on the generation of a plasma out of single colloid particles by means of an intense, pulsed laser beam, and the detection of the subsequent plasma light emission. The difference in breakdown thresholds from liquid to solid matter is the basic principle behind LIBD; they are lower for solid matter. Thus the laser beam energy is at- tenuated sufficiently so that pure liquid shows no break- down events. In the presence of colloidal particles, how- ever, the breakdown threshold in the focal volume is ex- ceeded. The number of breakdown events per number of laser shots results in a breakdown probability, dependent on particle concentration and size. For determination of colloid size, light emissions from single plasmas are de- tected by a microscope CCD camera system. The spatially resolved detection of the plasma light emissions results in Tobias Bundschuh · Jong-Il Yun · Roger Knopp Determination of size, concentration and elemental composition of colloids with laser-induced breakdown detection/spectroscopy (LIBD/S) Fresenius J Anal Chem (2001) 371 : 1063–1069 DOI 10.1007/s002160101065 Received: 30 April 2001 / Revised: 19 July 2001 / Accepted: 23 July 2001 / Published online: 27 October 2001 SPECIAL ISSUE PAPER Parts of this contribution have been shown during a poster presentation (1 st poster award) at the Colloquium Analytical Atomic Spectroscopy, CANAS ‘01, Freiberg, March 2001 T. Bundschuh (✉) Research Center Karlsruhe GmbH, Institute for Technical Chemistry, Water Technology and Geotechnology, P.O. Box 3640, 76021 Karlsruhe, Germany e-mail: tobias.bundschuh@itc-wgt.fzk.de J.-I. Yun Research Center Karlsruhe GmbH, Institute for Nuclear Waste Management, P.O. Box 3640, 76021 Karlsruhe, Germany R. Knopp Lawrence Berkeley National Laboratory, The Glenn T. Seaborg Center, Chemical Sciences Division, MS 70A-1150, 1 Cyclotron Road, Berkeley, CA 94720, USA © Springer-Verlag 2001