Retention mechanisms of amitriptyline and its impurities on amide, amino, diol, and silica columns in hydrophilic interaction liquid chromatography

Hydrophilic interaction liquid chromatography (HILIC) has been widely applied to challenging analysis in biomedical and pharmaceutical fields, bridging the gap between normal-phase high-performance liquid chromatography and reversed-phase high-performance liquid chromatography (RP-HPLC). This paper comprehensively explores the retention mechanisms of amitriptyline and its impurities A, B, C, D, F, and G on amide, amino, diol, and silica columns. Dual HILIC/RP-HPLC retention mechanisms were developed, and transitional points between HILIC and RP-HPLC mechanisms were calculated on amide, diol, and silica columns. Adsorption and partition contributions to overall retention mechanisms were evaluated using Python software in HILIC and RP-HPLC regions. The cation exchange mechanism dominates overall retention for ionized analytes in the silica column (R² > 0.995), whereas the retention of ionized analytes increases with pH. Impacts of acetonitrile content, buffer ionic strength, and pH, along with their interactions on the retention of ionized analytes in the silica column, were determined using the chemometric approach. Acetonitrile content showed the most significant impact on the retention mechanisms. These findings highlight that a detailed investigation into retention mechanisms provides notable insights into factors influencing analyte retention and separation, promising valuable guidance for future analysis.