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Optimizing Performance
Fast Injection Cycle and Low Delay Volume
Fast Injection Cycle and Low Delay Volume
Short injection cycle times for high sample througput is one of the main
issues in analytical laboratories. Shortening cycle time starts with:
• shortening column length
• high flow rate
• 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, as soon as 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 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.
NOTE Having the valve in bypass position can increase the carry-over in the system.
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 sec. 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.
NOTE 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 the retention times are prolonged for the last run. Especially at
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