A method for evaluating and/or qualify the performance of a separation system, the system comprising a parallel assembly, an inlet fluid path entering the parallel assembly and an outlet fluid path leaving the parallel assembly, said parallel assembly comprising parallel fluid paths (F1',F2',... Fn') each comprising a separation module (M1',M2',...Mn') in the form of a chromatography module, said method comprising the steps of: providing a sensor (S1,52,...Sn) of the same type in either all of said parallel fluid paths, or, in all of said parallel fluid paths except one; measuring a characteristic fluid property using said sensors to generate a response curve for each sensor; measuring the same characteristic fluid property with a system sensor of the same type positioned in the outlet of the separation system to generate a system response curve; and comparing response curves to evaluate and/or qualify the performance of the separation system, the system being characterised in that the response curves are evaluated to determine: a) average residence time in the respective response curve (53, 55, 57) for each module in the parallel assembly wherein said average residence times are compared to the average residence time in the response curve of the system; b) chromatographic efficiency in terms of width of curve peaks (53, 55, 57) for each module in the parallel assembly wherein said widths of curve peaks are compared to the width of a peak for the response curve of the system, or c) symmetry of curve peaks (53,55,57) for each module in the parallel assembly wherein said symmetries of curve peaks are compared to the symmetry in the response curve of the system. providing a sensor (S1,52,...Sn) of the same type in either all of said parallel fluid paths, or, in all of said parallel fluid paths except one; measuring a characteristic fluid property using said sensors to generate a response curve for each sensor; measuring the same characteristic fluid property with a system sensor of the same type positioned in the outlet of the separation system to generate a system response curve; and comparing response curves to evaluate and/or qualify the performance of the separation system, the system being characterised in that the response curves are evaluated to determine: a) average residence time in the respective response curve (53, 55, 57) for each module in the parallel assembly wherein said average residence times are compared to the average residence time in the response curve of the system; b) chromatographic efficiency in terms of width of curve peaks (53, 55, 57) for each module in the parallel assembly wherein said widths of curve peaks are compared to the width of a peak for the response curve of the system, or c) symmetry of curve peaks (53,55,57) for each module in the parallel assembly wherein said symmetries of curve peaks are compared to the symmetry in the response curve of the system. a) average residence time in the respective response curve (53, 55, 57) for each module in the parallel assembly wherein said average residence times are compared to the average residence time in the response curve of the system; b) chromatographic efficiency in terms of width of curve peaks (53, 55, 57) for each module in the parallel assembly wherein said widths of curve peaks are compared to the width of a peak for the response curve of the system, or c) symmetry of curve peaks (53,55,57) for each module in the parallel assembly wherein said symmetries of curve peaks are compared to the symmetry in the response curve of the system.