Sample preparation systems and methods are described having pump control, valve configurations, and control logic that facilitate automatic, inline preparation dilutions of a sample according to at least two dilution operating modes. A system embodiment includes, but is not limited to a first pump configured to drive a carrier fluid; a second pump configured to drive a diluent; and a plurality of selection valves fluidically coupled with the first pump and the second pump, the plurality of selection valves being configured to direct fluid flows from the first pump and the second pump according to at least two modes of operation to provide a single-stage sample dilution according to a first operating mode and to provide a dual-stage sample dilution according to a second operating mode.