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5 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 most
important requirements in analytical 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, 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.
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
Having the valve in bypass position can increase the carry-over in the system.
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