Discussion
The goal of this study was to develop a technique that provides detailed information
on the size distribution of unlabeled submicron and nano-sized inorganic
particles in toxicology samples. Specifically, we wanted to be able show directly
by instrumental analysis whether visible particle clusters, such as are shown in Figure 1B, contain nano-sized primary particles. Elemental analysis and radioactive
labeled particles provide mass concentration data but not size data. Microscopybased techniques provide size data only after image analysis of a sufficient sample to get accurate statistics. Manual image analysis is labor intensive and automated image analysis is subject to artifacts from overlapping particles or poor contrast from the background. SdFFF complements the available techniques by providing detailed size distributions from each sample run.
The sample handling methods used this study involved particle dispersion by
ultrasound in the presence of a surfactant to demonstrate the presence of a mode corresponding to the primary particle size of the test particle. Characterizing thesize distribution of particle aggregates in biological samples is a complex problem that is outside the scope of this pilot study. Particle aggregation is a dynamic process since aggregates are held together by weak surface forces. Aggregate size can be changed by mechanical force as well as by changes in pH, ionic strength, and
concentration of surfactants.