Chromatography Forum

Does the sample in SFC absolutely have to be injected as a slug (small, discreet amount), or can it be fully dissolved into all of the mobile phase before the mobile phase gets to the columns? I've read that the sample is introduced as a slug to prevent the detected band from being broad and lacking resolution, but I am curious if I could still yield useful results without adding the sample this way.

Of couse it needs to be introduced by an injection method, otherwise all it would be is an impurity and constant background in your eluant.

The only way it would work would be if you introduce the sample in a large volume and at the initial mobile phase conditions it will be completely retained on the column, then by altering the mobile phase composition you cause the analyte to be eluted. This would work the same as solid phase extraction and would allow for a large volume of low concentration sample to be introduced for more sensitivity.

If the column does not completely retain the analyte at initial mobile phase conditions then you would get either a very very broad peak or as CE Instruments said, it would merely be a constant background signal. If you are working with very high analyte concentrations I guess you could introduce sample this way and simply measure change in background signal between mobile phase with the analyte and mobile phase without analyte and calibrate as you would a spectrophotometer by signal intensity, but if you do this there would be no need for a column, just use it as a flow cell type instrument.