A Look at Column Choices

Importance of the Topic

Chromatographic column selection is a critical factor in analytical chemistry, directly impacting separation efficiency, resolution, analysis time and method robustness. Advances in particle design, bonding chemistries and column formats enable tailored solutions for small molecules, peptides, proteins and polar analytes. Understanding how column properties such as pore size, particle structure and surface chemistry influence chromatographic performance is essential for successful method development in pharmaceutical, biotechnological and industrial applications.

Objectives and Study Overview

This work reviews key considerations when choosing a reversed-phase or HILIC column, with emphasis on superficially porous (core-shell) technologies. It illustrates:

• Column chemistry factors: silica surface, bonded phases and end-capping.
• Particle architectures: totally porous vs superficially porous.
• Operational parameters: mobile phase composition, pH range and pressure limits.
• Method development strategies to optimize selectivity, efficiency and lifetime under low, mid and high pH conditions.

Methodology and Instrumentation

Column characteristics were systematically compared using HPLC and UHPLC systems under gradient and isocratic conditions. Key methodological steps include:

• Evaluating different bonded phases (C18, C8, phenyl-hexyl, polar-embedded, CN, PFP, HILIC) to modify selectivity.
• Adjusting pore size (80–450 Å) to match analyte size (small molecules vs peptides/proteins).
• Selecting particle size (1.8–5 µm, core-shell 2.7 µm or 4 µm) to balance efficiency and backpressure.
• Fine-tuning mobile phase composition (organic modifier type and percentage) and pH (range 1–12).

Main Results and Discussion

Core-shell (Poroshell 120) columns consistently delivered higher plate counts (≈12,000–32,000 per 15 cm) at 40–50% lower pressure compared to sub-2 µm fully porous particles. Van Deemter analysis highlighted reduced mass transfer resistance (lower C term) and improved longitudinal diffusion (B term) for superficially porous materials. Method case studies demonstrated:

• Steroid and beta-blocker separations: phenyl-hexyl and Bonus-RP phases provided superior resolution.
• NSAID profiling: pentafluorophenyl (PFP) chemistry offered orthogonal selectivity to C18.
• High pH reversals: HPH-C18/C8 enabled improved retention of basic compounds in neutral form with acceptable column lifetime.
• HILIC applications: bare silica provided strong retention for polar catecholamines under acetonitrile-rich mobile phases.

Benefits and Practical Applications

By selecting the appropriate combination of pore size, particle type and bonded phase, analysts can achieve:

• Faster separations with minimal compromise on efficiency.
• Enhanced selectivity to resolve closely related or isomeric compounds.
• Extended column lifetimes across a wide pH range (1–11) for diverse analytes.
• Streamlined method development using phase selectivity kits.

Future Trends and Potential Applications

Emerging directions include expansion of core-shell formats to larger pore diameters for biomolecule separations, development of novel polar-embedded and mixed-mode phases, and integration with high-throughput UHPLC platforms. The adaptation of column chemistries for high-pH stability and HILIC modes will further broaden analytical capabilities for challenging polar and ionizable compounds.

Conclusion

Optimizing column selection by leveraging advances in superficially porous particle technology and diverse bonded phases enables robust, high-performance separations. A structured method development approach—adjusting mobile phase, pH and phase chemistry sequentially—ensures rapid identification of the most suitable column for any analyte class.

Used Instrumentation

• High-Performance Liquid Chromatography (HPLC) systems (≤600 bar).
• Ultra-High Performance Liquid Chromatography (UHPLC) systems (≤1200 bar).
• Core-shell columns (e.g., Poroshell 120 family, AdvanceBio RP-mAb).
• Detection: UV diode array detectors at 254 nm and 280 nm.