2306 cept. In part, a possible explanation may be attributed to the influence of sucrose and other excipients at low protein concentration (discussed further later). Hawe, Hulse, Jiskoot and Forbes A hydrodynamic radius of about 5.6–5.9 nm was obtained by TDA and DLS for the concentration range from 0.5 to 5 mg/ml for adalimumab (Fig. 1d), which is the typical size for monomeric IgG (24–27). The slightly larger radius (7.5–8.3 nm) for the concentrated 50 mg/ml sample can be explained by reversible self-association, which is often observed for monoclonal antibody formulations at high concentrations (28). Again, the rzave determined for 0.05 mg/ml adalimumab was too high (27.7 nm), whereas rh (TDA) and rmain peak (DLS) were still accurate. In the concentration range from 0.5 to 50 mg/ml, TDA and DLS were comparable to correctly determine the size of BSA, etanercept and adalimumab in the tested formulations. However, for the lowest concentra- tions of 0.05 mg/ml, TDA proved to be superior over DLS. The same behavior was identified for sizing of the small peptide oxytocin. When measuring formulations of low oxytocin concentrations, especially the rzave values in DLS were far too high. TDA was capable of correctly determining the correct size of oxytocin and the proteins at low concentrations. Fig. 2 Comparison of radius from TDA with Zaverage radius from DLS (a, zoom as b), and the radius of the main peak from DLS (c) for the different peptides and proteins measured at concentrations between 0.05 and 50 mg/ml. The results are shown as average ± standard deviation of n=3 (DLS) and n=5 (TDA) individual measurements. Fig. 3 Radius (Zaverage radius, radius main peak) and polydispersity index (PDI) from DLS and Taylor dispersion analysis for etanercept (a) and adalimumab (b) diluted with formulation placebo. The results are shown as average ± standard deviation of n=3 (DLS) and n=5 (TDA) individual measurements.