[Construction of acrylpimaric acid-bonded silica stationary phase and its application in mixed-mode chromatographic...

The development of novel functional materials from renewable biomass resources has garnered widespread attention. This strategy not only effectively reduces the reliance on petrochemical raw materials in the preparation process， thereby reducing carbon emissions and mitigating environmental pollution， but also enhances their added value， promoting the development of related agriculture and forestry industries. In this study， we prepared acrylpimaric acid bonded on silica （Sil-APA） as a new stationary phase by linking the functional ligand to silica using γ-glycidoxypropyltrimethoxysilane as the silane coupling agent. The synthesized stationary phase was characterized by Fourier-transform infrared spectra （FT-IR）， elemental analysis （EA）， zeta potential analysis， and thermogravimetric analysis （TGA）. Acrylpimaric acid was successfully immobilized onto the surface of spherical silica via a ring-opening reaction involving the epoxy and carboxyl groups. Analytes and the stationary phase experience multiple interactions during the separation process owing to the coexistence of functional groups such as hydrogenated phenanthrene rings， as well as hydroxyl， carbonyl， and carboxyl groups on the surface of the Sil-APA stationary phase. Synergy involving multiple interaction mechanisms improves the separability and applicability of the Sil-APA stationary phase. We used hydrophobic， hydrophilic， and ionic compounds to probe the effects of organic-phase content， pH， and buffer-salt concentration in the mobile phase on the chromatographic performance of the Sil-APA column. The logarithm of the retention factor （log k） for alkylbenzenes in the stationary phase was found to decrease with increasing methanol content in the mobile phase during reverse-phase liquid chromatography （RPLC）； hence， the Sil-APA stationary phase exhibited typical reverse-phase retention behavior. The Sil-APA column exhibited stronger aromatic selectivity and weaker hydrophobic selectivity compared to a C18 column， which enables polycyclic aromatic hydrocarbons （PAHs） to be more-strongly retained than alkylbenzenes while also separating these hydrophobic compounds in less time. The ln k for nucleosides/bases on the stationary phase decreased with increasing water content in the mobile phase in hydrophilic interaction liquid chromatography （HILIC） mode， confirming that the Sil-APA column has typical hydrophilic retention characteristics for the separation of nucleosides/bases. Furthermore， the relationship between the pH and buffer-salt concentration of the mobile phase and ln k for nucleosides/bases reveals that hydrogen bonding and electrostatic interactions between the stationary phase and the analytes play important roles in addition to hydrophilic interactions. The ln k for ionic compounds was observed to decrease with increasing buffer-salt concentration in the mobile phase in ion-exchange chromatography （IEC） mode， while concurrently increasing with the pH of the mobile phase. These results demonstrate that the Sil-APA column exhibits classical cation-exchange behavior for the separation of cationic compounds. These multiple retention mechanisms render the Sil-APA column suitable for mixed-mode liquid chromatography （MMC）. The Sil-APA column exhibits good separation selectivity for different analyte components， further demonstrating its mixed-mode chromatographic performance and potential for complex sample analysis. Furthermore， Sil-APA demonstrated excellent chromatographic repeatability， stability， and reproducibility， as evidenced by low retention-time relative standard deviations （RSDs） of 0.076%-0.356% （n=10）， 0.05%-0.193% （n=5）， and 0.498%-2.806% （n=4） for inter-day， inter-day， and batch-to-batch precisions， respectively. In summary， we designed and prepared an acrylic-acid-modified silica stationary phase material for use in liquid-chromatography applications. The excellent separation performance observed under mixed-mode conditions demonstrates that acrylpimaric acid can possibly be used a functional stationary-phase monomer， thereby potentially broadening the applications scope of resin acids in separation science. The facile preparation of Sil-APA and its promising applications scope may also provide new concepts for the development of stationary-phase materials based on natural-product-modified silica in the liquid-chromatography field.