LEVEL: INTERMEDIATE

A ggregation is a major problem for long-term storage stability of therapeutic proteins and their shipping and handling, as has been extensively reviewed (1). We discussed the mechanisms of protein aggregation at length in Part 1 of this review (2). As we also described there, although size exclusion chromatography (SEC) has generally been the routine method for detecting and quantifying protein aggregation (3–5), a major drawback of SEC is the loss of aggregates by their nonspecific binding to the column (6, 7). Thus, column (matrix)-free techniques, such as analytical ultracentrifugation (AUC), field-flow fractionation (FFF)