A new analytical method used rubidium chloride density-gradient ultracentrifugation to resolve and quantify dual-AAV gene therapy vectors. The approach aims to separate two highly similar full capsids and provide more accurate measurement in dual-vector products. This matters because vector quantification errors can complicate comparability across batches and potentially affect dosing consistency. Better characterization can support quality control for dual-AAV platforms, where physicochemical similarity has historically made separation challenging. For gene therapy developers and CDMOs, the work adds a practical toolkit option for capsid-level analytics supporting release testing and process development.