Comprehensive evaluation of zwitterionic hydrophilic liquid chromatography stationary phases for oligonucleotide characterization

Hydrophilic interaction chromatography (HILIC) has been proposed as a valuable alternative to ion-pairing reversed-phase chromatography (IP-RPLC) for oligonucleotide (ON) analysis. In this context, the potential of seven zwitterionic HILIC columns has been evaluated against amide- and poly-hydroxy fructan-functionalized HILIC columns and a C18 column operated under IP-RPLC mode. Based on the retention characteristics of key small molecule pairs, each zwitterionic HILIC column showed a unique radar-shaped profile, suggesting different selectivities for distinct structural differences. Unmodified DNA and RNA samples were then evaluated, and the columns classified based on their retentivity. Two zwitterionic columns were particularly promising in terms of overall resolution, especially for the largest ONs (> 40-mer). Finally, separations between a chemically modified drug-like ON and its closely related impurities were performed. Although the ZIC-cHILIC column showed similar selectivity values as compared to the reference IP-RPLC technique, all columns demonstrated a general decrease in selectivity due to the minor structural differences present in the highly complex samples. This work highlights the utility of zwitterionic HILIC mode for ON analysis and it reveals the importance of understanding columns characteristics - in terms of retention and selectivity - when selecting a stationary phase for specific ON applications.

Highly selective separation of aminoglycoside antibiotics on a zwitterionic Click TE-Cys column

Hydrophilic interaction liquid chromatography has emerged as a valuable alternative approach to ion-pair chromatography for the separation of aminoglycoside antibiotics in recent years. However, the resolution of structurally related aminoglycosides is a great challenge owing to the limited selectivity. In this work, a cysteine-based zwitterionic stationary phase (named Click TE-Cys) was utilized and compared with five commonly used hydrophilic interaction liquid chromatography columns. Click TE-Cys displayed much better selectivity for structurally similar aminoglycosides. The retention behaviors of aminoglycosides were investigated in detail, revealing that low pH (2.7 or 3.0) and high buffer concentration (≥50 mM) were preferable for achieving good peak shape and selectivity. Effective resolution of ten aminoglycosides including spectinomycin, dihydrostreptomycin, streptomycin, gentamicin C1, gentamicin C2/C2a, gentamicin C1a, kanamycin, paromonycin, tobramycin, and neomycin was realized at optimized conditions. Additionally, spectinomycin and its related impurities were successfully resolved. The results indicated the great potential of the Click TE-Cys column in the separation of aminoglycoside mixtures and related impurities.