User manual

Agilent 1260 Infinity High Performance Autosampler User Manual 67

Optimizing Performance

How to Configure the Optimum Delay Volume

For very fast gradients over 0.5 min the delay volume of the system can

be easily reduced without changing the physical configuration of the

system. The change is achieved by changing the behavior of the

autosampler.

The 270 µL delay volume of the autosampler is due to the flow path from

the injection valve through the metering device, needle, needle seat and

connecting capillaries back to the injection valve (see Figure 16 on

page 68). To make an injection the valve switches from mainpass to

bypass so that the metering device can draw the sample into the needle

capillary. The injection is made when the valve switches back to mainpass

and the sample is flushed onto the column. The valve remains in this

position during analysis so that the autosampler is continually flushed and

hence the gradient has to flow through this delay volume to reach the

column. This can be eliminated by switching the injection valve from

mainpass to bypass after the injection has been made and the injected

sample has been flushed onto the column. In practice this can be done a

few seconds after injection and is activated by selecting the “Automatic

Delay Volume Reduction” (ADVR) function in the autosampler setup menu.

The Flush- out Factor (typically 5 times injection volume) ensures that

enough time is allowed to flush the sample out of the injector before

switching to bypass. For instance a 1 µL injection under standard

conditions effectively reduces the system delay volume by approximatly

250 µL.