Comparison of colloid investigations by single particle analytical techniques—a case study on thorium-oxyhydroxides

Characterization of complex systems such as colloids calls for the combination of a multitude of analytical methods. This work reviews some of the most common techniques used to gain information on the particle size distribution of a colloidal suspension. Fractionation by filtration or centrifugation is discussed as well as flow field fractionation and electron- and atomic-force microscopy. Since these delicately balanced systems are to be characterized with as little perturbation as possible, this work lays special emphasis on non-invasive methods such as light scattering (photon correlation spectroscopy (PCS), static light scattering: single particle counter) and laser induced breakdown detection, an in-situ method, which opens up a wide operational dynamic range, covering three orders of magnitude in size (5–1000 nm) and seven orders of magnitude in particle concentration (1 ppt-several ppm). Advantages and shortcomings of each technique are illuminated by means of an example, the characterization of ThOn(OH)m-colloids in over-saturated thorium solutions. Results obtained by atomic force microscopy (AFM)-, scanning electron microscopy (SEM)-, transmission electron microscopy (TEM)-, PCS- and laser induced breakdown detection (LIBD) measurements are compared and discussed.