This study introduces cSPRING (Continuous Titration Based Spectral Related Intensity Change), a method that measures a protein–ligand dissociation constant (Kd) in a single experiment. It builds on Flow Induced Dispersion Analysis (FIDA) and Taylor dispersion analysis combined with ratiometric fluorescence detection, generating a continuous dilution series inside a capillary instead of pipetting a separate sample for each titration point. Running on a Fida Neo system, cSPRING returns both the Kd and the ligand's hydrodynamic radius, cuts sample-preparation time roughly 8-fold, and needs only nanograms of protein. The authors validated it on hen egg white lysozyme with NAG3 and bovine carbonic anhydrase II with three inhibitors, spanning low-nanomolar to high-micromolar affinities, consistent with SPR, ITC and spectral-shift assays. A single Kd was measured in as little as 45 seconds.