Difference between Dwell and Delay Volume (Agilent OQ)

Discussions about HPLC, CE, TLC, SFC, and other "liquid phase" separation techniques.

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Hello,
I am a little bit desperate. The OQPQ for one of our systems was executed. Afterwards I checked the report. The report stated a delay volume about 0.26 ml. It is a 1290 quaternary system. My first guess was that the delay volume is the same thing as the dwell volume but agilent gives it a different name.

I checked the method which was used to determine the delay volume and noticed that the jetweaver with an internal volume of 350 µl was activated. This means it can not be the same as the dwell volume as the dwell volume has to be higher than 350 µl because the jetweaver is between the gradient proportioning valve and the detector. The OQ Report discloses the following equations for the delay and dwell volume

Delay Volume = ("calculated start of composition step" - "set start of composition step) x flow rate

Dwell Volume = ("set time of changing gradient mix" - "time to reach % of composiont) x flow rate

To be frank, I can't see any differences. Could anyone of you help me understanding the difference between the dwell volume and the delay volume. Another question that I have: Why is it useful to know the delay volume. I completely understand why it's important to know the dwell volume but after all those years of liquid chromatography experience I have never had to deal with such thing like the delay volume.

Many thanks for your support in advance.

barrelproof
If you think of "calculated start of composition step" as the time you expect to see a baseline deflection due to change in composition (based on your recorded Vd), then Delay Volume is what you use when you need to synch up the signals collected by different detectors in series.
Dwell Volume is a function of volume and flow rate for the plumbing between your gradient formation point and detector (less the column volume). It is something you have to be aware of when transferring gradient methods to different LCs.
Delay volume is the extra volume between detectors. It matters when you want to overlay plots and have your peaks line up, and it is settable somewhere in your processing method as something you can compensate for.
Thanks,
DR
Image
barrelproof wrote:
Dwell Volume = ("set time of changing gradient mix" - "time to reach % of composiont) x flow rate

It seems to me that this quantity is negative.

I guess that the difference between the two questioned quantities results from the difference between the "time to reach % of composiont" and the "calculated [from the actual experimental data?] start of composition step". The step starts earlier than the particular % is reached. The original OQ reports would be helpful.
Hello,
Apologize for this question but are you sure that JW is physically instslled on your system, not just configured? Not sure if this part have a tag.

I can imagine also that the paths inside could be partially blocked result in lowering volume.
Regards,
pksik
Dwell Volume is a function of volume and flow rate for the plumbing between your gradient formation point and detector (less the column volume).tiny fishing
Delay volume is the extra volume between detectors
Knowing the delay volume because delay volume affects the throughput and also the transfer in a gradient method from one system to another.
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