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).