What is "means by delay volume" in HPLC analysis?

Mean delay volume, also called dwell volume, is the volume between the point where the high pressure liquid chromatography gradient is mixed and the column inlet. The delay volume is determined by measuring the delay between the programmed time and the actual time at which the gradient occurs.

The HPLC delay volume is defined by the volume of tubing between the gradient mixer and the pump, the pump, and the injector. The delay caused by the delay volume can make a difference in the appearance of the chromatogram for different gradient systems. It is important to know the mean delay volume of each system in order to compensate for it in the analysis of the HPLC chromatogram.