Technical data

54 Agilent 1290 Infinity LC System Manual and Quick Reference
3 Optimization of the Agilent 1290 Infinity LC System
How to Achieve High Throughput
The injection can be optimized for speed remembering that drawing the
sample too fast can reduce the reproducibility. Marginal gains are to be made
here as the sample volumes used tend towards the smaller end of the range in
any case. A significant portion of the injection time is the time taken with the
needle movements to and from the vial and into the flush port. These
manipulations can be performed while the previous separation is running.
This is known as "overlapped injection" and it can be easily turned on from the
autosampler setup screen in the ChemStation Control Software. The
autosampler can be told to switch the flow through the autosampler to bypass
after the injection has been made and then after, for example, 3 minutes into a
4 minutes run to start the process of aspirating the next sample and preparing
for injection. This can typically save 0.5 to 1 minute per injection. For sticky
compounds it is recommend to do this during column equilibration, when the
autosampler has seen the starting conditions of the next gradient run.
The column equilibration step can be a significant part of the cycle time.
Typically the column needs flushing with three to five times the column
volume to stabilize it ready for the next injection and this can be 50 % or more
of the separation time in some applications. It is an essential process but can
be taken out of the cycle time by using automated alternating column
regeneration. For this a two-position ten-port, 1200 bar, valve head is required
in the column compartment; a second analytical column, identical to the first;
and a second pump is needed. As one column is being used in the separation
run, the other column is being flushed with the starting composition of the
mobile phase gradient and to start the next injection the newly re-equilibrated
column is switched into the analytical flow path. The two columns then
alternate in this way for the whole sequence of injections. The second pump is
only required to flush an isocratic mixture through the column and so can be a
simpler pump than the 1290 Infinity pumps. For instance a 1200 Series
isocratic pump would be sufficient to perform this task. The setup is
illustrated in Figure 22 on page 55.