3.2. Deactivation of the liner with ionic liquids Because of their low volatility, a minimal leaching by evaporation was expected when ILs were used for deactivation of the liner. Furthermore, we selected ILs that are thermally stable enough to last for a few hundred injections [32–34]. The selected ILs are displayed in Fig. 1. Deactivation was done according to the procedure described in Section 2.3.
3.2.1. N-ethyl-N,N,N,N-tetramethylguanidinium tris(pentafluoroethyl)trifluorophosphate ([emtg][FAP]) Injection of BDA-standards of 1–50 mM after deactivation with[emtg][FAP] revealed that although at higher concentrations the shape and size of the peaks from consecutive injections were nicely reproducible (except for every first injection showing a lower peak area), the detection limit was as high as 20 mM (1760 ppm). Thus,
although the PF6− anion was previously reported as a strongly adsorbing to the silica-based support [35], the shielding performance of the selected FAP phosphate anions did not work out as expected. An explanation may be that the analytes in the present
work contain proton accepting groups, and thus due to the presence of the PF6 − anion they are strongly retained on the created shielding surface [30].