A system for controlling peristaltic pumps includes a first peristaltic pump configured to drive a carrier fluid, a second peristaltic pump configured to drive a diluent fluid, a third peristaltic pump configured to drive an internal standard, spike or matrix solution, and a controller for adjusting respective flow rates of the first, second, and third peristaltic pumps. The controller is configured to run the second peristaltic pump at least at a minimum predetermined flow rate whenever the third peristaltic pump is active.