# Plate Theory and Extensions - Chromatographic Dead Volumes > Page 33

# Chromatographic Dead Volumes

The two so
called "dead volumes" are important in both theoretical studies and
practical chromatographic measurements. They are the *kinetic dead volume* and the *thermodynamic
dead volume*. The kinetic dead volume is used to calculate linear
mobile phase velocities and capacity ratios in peak variance studies. The
thermodynamic dead volume is relevant in retention measurements for
identification purposes, thermodynamic studies and, in particular, for
constructing vant Hoff curves.

In equation
(39) (for an incompressible mobile phase) the kinetic dead volume (which is the
volume of moving phase only) is (V_{i(m)}). Thus, at a flow rate of (Q)
ml/s, the dead time (t_{o}) would be given by,

and, thus, the linear velocity (u) of the mobile phase is,

where (_{}) is the column length

In equation (39), the thermodynamic dead volume is given by

V_{I(m)} + YV_{I(S)} + WV_{p}_{(1)}