Influence of cations and anions of ionic liquids and salts as additives in RP HPLC systems to the analysis of alkaloids on C18 and Polar RP columns

The ionic nature of basic compounds gives rise to broad asymmetrical chromatographic peaks in RP systems containing a mixture of organic modifiers and water as mobile phases. The addition to the mobile phase of a reagent to block the silanol sites such as salts containing chaotropic anions or ILs gives significantly more symmetric peaks and a high resolution of basic analytes. In systems containing the addition of salts or ILs, the retention of ionic analytes is a consequence of the combination of a mixed mechanism that involves chaotropic, ion-exchange, hydrophobic, and ion-pairing interactions. In this work, the influence of salts consisting of various anions and ILs consisting of various cations and anions on the retention and peak symmetry of alkaloids in RP HPLC systems on C18 and Polar RP columns was investigated. The multiple interactions that salts and ILs experience inside the chromatographic system suggest that the alkaloid-suppressing potency should be measured based on the shape of the chromatographic peaks. In order to better understand the retention mechanism, the retention and symmetry of peaks obtained on both stationary phases and in systems containing salts and ILs were compared.