# Gas Chromatography - Gas Supplies > Flow Programmers > Page 12

Then _{} (6)

and n = T_{t(0), }where_{ }(T_{t(0)})
will be the retention time of the solute under the defined pressure programming
conditions.

Taking a
simple practical situation where the retention volume is 1000 ml on a given
column operating at a (g) value of 2
and the retention time of the solute is 10 minutes (600 seconds). The flow
properties of the column *i.e*. _{} can be defined in the following manner,

From
equation (3) _{}

or _{}. Thus, _{}

Substituting
for _{} in (6),_{} (7)

Equation (7) can now be employed to calculate the change in retention time for a series of solutes separated under pressure programming conditions in the defined column