This is a copy of the slides presented at the meeting but not formally written up for the volume.

Interest in nanotechnology is rapidly growing as applications for nanoparticles in drug delivery and as image contrast agents are realized. Nanoparticles, as the name implies, refers to particles with sizes ranging from a few nanometers to hundreds of nanometers. Based on this definition, it is size which differentiates nanoparticles from all other particles. Also, it is size which will contribute to the properties of the nanoparticles and determine ultimately its function and efficacy in real-world applications. Thus it is important to properly characterize the size of nanoparticles. Light scattering (static and dynamic) is a non-invasive technique for measuring particle size and size distribution in solution. Measurements can be made in batch or flow mode. In the case of batch mode, the average size of the nanoparticle is determined. Thus if the sample contains impurities or aggregates, the size would be skewed and inaccurate. To accurately determine size, some type of separation would be needed. Size Exclusion Chromatography (SEC) is a separation technique used for determining purity of a sample and is based on the molecular size of the sample components. Coupled with a multiple angle laser light scattering (MALLS) and inline dynamic light scattering (DLS) apparatus, the size can be determined for the fractionated sample. The sizes of several different nanoparticles were measured in batch and flow mode and the implications of the size results are discussed. Nanoparticles studied include dendrimers, liposomes, and metal particles. Finally, these results are used to establish standard protocols for size characterization of nanoparticles.