Abstract: A system for controlling fluid flow comprises a first fluid conduit having a length, an inner diameter, an input pressure and an output pressure, and a second fluid conduit having a length, an inner diameter, an input pressure and an output pressure where the output pressure of the first fluid conduit is the input pressure of the second fluid conduit. The system also comprises a pressure sensor configured to determine the output pressure of the first fluid conduit, and a controller configured to control the output pressure of the first fluid conduit, thereby establishing a desired fluid flow through the second fluid conduit based on the length of the second fluid conduit, the inner diameter of the second fluid conduit, the temperature of the second fluid conduit and the type of fluid flowing in the second fluid conduit.

Abstract: A single stage flow modulator for performing comprehensive chromatography comprises a first chromatographic column, a valve fluidically coupled to at least two fluid conduits, wherein when in a first position, the valve directs a control flow to direct an output of the first chromatographic column to a first detector, and wherein when in a second position, the valve directs a control flow to direct a portion of an output of the first chromatographic column to a second chromatographic column, wherein the portion of the output of the first chromatographic column directed to the second chromatographic column is continuously modulated throughout a sample run.