# Plate Theory and Extensions - The Retention Volume of a Solute > Page 11

# The Retention Volume of a Solute

The retention
volume of a solute is that volume of mobile phase that passes through the
column between the injection point and the peak maximum. Consequently, by
differentiating equation (10), equating to zero and solving for (v), an
expression for the retention volume (V_{r}) can be obtained.

Restating equation (12),

=

Equating to zero and solving for (v), then at the peak maximum,

n - v = 0 or v = n

Thus, the peak
maximum is reached after (n) *plate volumes* of mobile phase have passed
through the column. Consequently, the retention volume in **ml of mobile phase**
must be obtained by multiplying by the 'plate volume', (v_{m }+ Kv_{s}).