A global fit allows shared parameters across all data obtained for one series of measurements at different denaturant concentrations, which restricts the model and makes fitting more robust. The residency time (retention time) of the samples should be independent of urea after normalizing the data based the viscosity increase and was therefore shared between all samples. The hydrodynamic radius of the monomer was shown to be independent of denaturant and could thus be represented with Gauss curves with shared widths (Eq. 6) but different total areas which were defined by the isodesmic polymerization model (Eq. 8, ) multiplied with a constant to relate fluorescence to concentration.