Feed Injection provides a pre-pressurized sample, which is injected into the CO2 stream before the column by a syringing process. Before the sample is drawn, the connected loop, needle and seat are cleaned by purging with wash solvent. Meanwhile, the SFC pump is connected to the column. After drawing the specified sample volume, it is pre-pressurized in the loop to the pressure of the system. The pre-pressurized loop containing the sample is connected to the CO2 stream coming from the analytical SFC pump and leading to the column. In this position, the sample can be injected by a syringing process with variable injection speed. In addition, to flush the complete sample out of the loop, an overfeed volume can be specified.
Two instrument parameters control the injection:
Feed Speed | For standard injections (0.1 - 10 µL), the Feed Speed should typically be higher than 100 µL/min (default 400 µL/min, maximum 1000 µL/min) to avoid peak broadening. A lower Feed Speed could be used for trapping injections in an initial isocratic step. |
Overfeed Volume |
The Overfeed Volume should not be below 2 µL (default 4 µL) to avoid possible loss of sample. Higher values could be used to flush out sticky compounds or heavy matrix-loaded samples. |