Dead volume (dead volume, V0) – the space from the injector inlet to the detector flow cell that is not occupied by the stationary phase. It includes 4 parts: the volume of the pipeline from the injector to the chromatographic column, the gap between the stationary phase particles in the column (occupied by the mobile phase, Vm), the volume of the column outlet pipeline, and the volume of the detector flow cell. Among them, only Vm participates in the chromatographic equilibrium process, and the other 3 parts only play a role in peak expansion. To prevent peak expansion, the volumes of these 3 parts should be minimized.
Dead time (dead time, t0) – the retention time of the unretained component. That is, the time for the mobile phase (solvent) to pass through the chromatographic column.
Measuring the dead volume of the system usually requires experimental measurement. The common method is to inject a special solution that has no effect on the stationary phase of the chromatographic column (there will be regulations in the method, such as: uracil, a small amount of NaNO3 or methanol dissolved in the mobile phase, and there are also cases where 100% chromatographic pure methanol is directly injected). A chromatographic peak will be obtained, and the dead time (t0) can be measured from this peak. This is the actual measurement result of t0.
Then the dead volume of the system is obtained by calculation:
Dead volume (V0) = dead time t0×flow rate F of the mobile phase.