# Plate Theory and Extensions - The Column Dead Volume > Page 29

If the column
volume is (V_{c}) and contains a volume of mobile phase (V_{M}), a volume of stationary phase (V_{S}) and a volume of support (*e.g.,
silica*) (V_{Si}), then,

V_{c} = V_{M} + V_{S} + V_{Si}
(27)

Now,
V_{M} V_{m}

(V_{m})
is the *moving phase* and a significant amount of (V_{M}) will be static (*e.g.,* contained
in the pores). The same applies to the volume of stationary phase, (V_{S}), which is not the same as (V_{S}), as it may include material that is
unavailable to the solute due to exclusion.

Now, the volume of a cylindrical column will be given by

V_{c}
= pr^{2}l (28)

where (r) is the column radius,

and (l) is the column length.

Hence,
V_{M}+ V_{S }+ V_{Si} = pr^{2}l
(29)

The individual
volumes, (V_{M}), (V_{S}) and (V_{Si}), can now be apportioned according to their
chromatographic pertinence.