By Yogeendra on Monday, July 22, 2002 - 01:36 am:
Delay volume in various LC models from various vendors. Alliance, Series 200, 1100 series
By yogeendra on Monday, July 22, 2002 - 01:38 am:
i want to know what are the volume with different system and how they minimise it
By Tom Mizukami on Monday, July 22, 2002 - 09:44 am:
The dwell volume is the system volume between the point of mobile phase mixing and the column inlet (normally measured to the detector).
The dwell volume for any system depends on its configuration. If you want to minimize the dwell volume you can switch to binary pumps that mix on the high pressure side and minimize the length and ID of connecting tubing. You can also bypass the pulse dampner, etc. Some systems like the 1100 can use an injector program to switch the sample loop and injector out of the flow path to futher minimize the dwell volume.
By yogeendra on Tuesday, July 23, 2002 - 01:02 am:
users of different systems can help me by providing the datas of their system.
By Uwe Neue on Tuesday, July 23, 2002 - 03:50 pm:
Why do you need to know? In modern systems, the software allows you to eliminate the gradient delay volume. I'll be glad to explain this.
By yogeendra on Monday, July 29, 2002 - 12:11 am:
pls explain it then either by sending me mail or replying in the forum
By Uwe Neue on Monday, July 29, 2002 - 04:37 pm:
When instruments with low-pressure gradient mixers are used, there is a volume between the point where the gradient is mixed and the column inlet. This delay volume comprises the volume of the tubing between the gradient mixer and the pump, the pump itself, the injector and associated tubing. The total volume can be measured by programming a step gradient and measuring the time from the programmed time of this step to the time at which it actually occurs. This is the volume by which the onset of any gradient is delayed.
In modern HPLC instruments, this delay volume can be largely or even completely avoided, by delaying the injection until the gradient reaches the inlet of the injector. On first glance, this might sound like a futile enterprise. However, we need to understand that the delay is also happening at the end of the gradient, at the wash cycle and the reequilibration cycle with the mobile phase. Therefore, I can also shorten the column reequilibration volume by the gradient delay volume. If I do this, I am running a gradient with the same speed as I would be able to do on a system without gradient delay volume. With the ability to use the delayed injection, I can eliminate the gradient delay volume nearly completely. I say nearly completely, because you can never delete the volume of the injector.