Delay Volume And Extra-Column Volume; Delay Volume - Agilent Technologies InfinityLab LC Series User Manual

5 How to Optimize the Performance of Your Module

Delay Volume and Extra-Column Volume

Delay Volume and Extra-Column Volume

The delay volume is defined as the system volume between the point of mixing in
the pump and the front of the column.
The extra-column volume is defined as the volume between the injection point
and the detection point, excluding the volume in the column.

Delay Volume

In gradient separations, this volume causes a delay between the mixture
changing in the pump and that change reaching the column. The delay depends
on the flow rate and the delay volume of the system. In effect, this means that in
every HPLC system there is an additional isocratic segment in the gradient profile
at the start of every run. Usually the gradient profile is reported in terms of the
mixture settings at the pump and the delay volume is not quoted even though
this will have an effect on the chromatography. This effect becomes more
significant at low flow rates and small column volumes and can have a large
impact on the transferability of gradient methods. It is important, therefore, for
fast gradient separations to have small delay volumes, especially with narrow
bore columns (e.g., 2.1 mm i.d.) as often used with mass spectrometric
detection.
The delay volume in a system includes the volume in the pump from the point of
mixing, connections between pump and autosampler, volume of the flow path
through the autosampler and connections between autosampler and column.
For the Flexible Pump, all pump parts downstream the MCGV contribute to the
delay volume, i.e. inlet weaver, pump heads, capillary connections, filters and the
optional Jet Weaver.
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