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 (Vi(m)). Thus, at a flow rate of (Q) ml/s, the dead time (to) 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

                                    VI(m) + YVI(S) WVp(1)