# Gas Chromatography - Gas Supplies > Flow Programmers > Page 9

## Flow Programmers

Flow programming is a procedure where the mobile phase flow-rate is increased during chromatographic development. If the mobile phase is compressible the relationship between retention volume, flow rate and inlet pressure is given by,

_{} (1)

Where (V_{r}) |
is the true retention volume of the solute, |

(V_{r(0)}) |
is the retention volume measured at the outlet. |

and (g) | is the inlet/outlet pressure ratio |

(for the derivation of this equation see The Thermodynamics of Chromatography)

Thus, _{}

Now, from
The Thermodynamics of Chromatography

_{} where (e) is a constant

Thus, _{} (2)

If (g) is large compared with unity, Then