It must be present in the mobile phase, it is optional in the sample only if you are injecting a small amount of sample with low number or molecules.

Thank you Omar

I am a bit wondering whether you have exactly got the point. My question is about sample preparation procedure when a non-polar sorbent is available only, so, we have to use ion-pair reversed phase reagent as an intermediate support to extract an ionic compound of interest from the sample before instrumental analysis. Please see the attachment bellow:

Thank you Navid for your comment,

As I told in my previous comment (please see the attachment too), my concern is sample preparation procedure NOT analytical stage. No mobile phase is used in ion-paired reversed phase solid phase extraction (IPRP-SPE).

Thank you Judith,

However, still more comments needed!