How is Dwell Volume Measured?

How is Dwell Volume Measured?

Dwell volume (sometimes referred to as delay volume) is calculated from the point where two solvents first mix to the head of the column. This encompasses the tubing, mixer, autosampler and column switch, if installed. Determining the dwell volume is one of the most essential tests which should be performed to understand an LC system as it differs between each system and plays an important role in gradient chromatography.

A gradient is a continuous change in mobile phase. However, the change is not instantly observed by the column due to the delay from where the mobile phase first meet to the column head. It can be measured using the conditions described in Figure 3, and hence calculated using the defined equations.

The %B range and flow rate should be representative of typical conditions used on the LC system. For example, a HPLC system typically uses 1 mL/min with 10-90%B over 15 minutes. The %B/min change is 80%B/15 mins which equates to 5.3%B/min. Thus, in the dwell volume test with a t_G of 10 minutes, the %B should cover the range of 53% i.e. 10-63%B over 10 minutes.