Agilent InfinityLab LC Series Vialsamplers User Manual 171
5 Optimizing Performance
Fast Injection Cycle and Low Delay Volume
Fast Injection Cycle and Low Delay Volume
Short injection cycle times for high sample throughput is one of the most
important requirements in laboratories. In order to shorten cycle times, you can:
• shorten the column length
• use high flow rates
• apply a steep gradient
Having optimized these parameters, further reduction of cycle times can be
obtained using the overlapped injection mode.
Overlapped Injection Mode
In this process, when the sample has reached the column, the injection valve is
switched back to bypass, and the next injection cycle starts but waits with
switching to mainpass (main path) until the actual run is finished. You gain the
sample preparation time when using this process.
Switching the valve into the bypass position reduces the system delay volume.
The mobile phase is directed to the column without passing sample loop, needle,
and needle seat capillary. This can help to have faster cycle times especially if
low flow rates have to be used like it is mandatory in narrow bore and micro bore
HPLC.
The injection cycle times also depend on the injection volume. In identically
standard condition, injecting 100
µL instead of 1 µL, increase the injection time
by approximately 8
s. In this case and if the viscosity of the sample allows it, the
draw and eject speed of the injection system has to be increased.
Having the valve in bypass position can increase the carryover in the system.
For the last injection of the sequence with overlapped injections, it has to be
considered that for this run the injection valve is not switched as for the previous
runs and consequently the injector delay volume is not bypassed. This means
that the retention times are prolonged for the last run. Especially at low flow
rates this can lead to retention time changes which are too big for the actual
calibration table. To overcome this, it is recommended to add an extra “blank”
injection as last injection to the sequence.
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