Choosing Appropriate Pore Size Columns for Size Exclusion Chromatography of Oligonucleotides

Significance of the Topic

Analytical size exclusion chromatography (SEC) is a cornerstone technique for evaluating size and purity of biomolecules. Applying SEC to oligonucleotides poses unique challenges due to their diverse lengths, secondary structures, and potential for nonspecific interactions. Selecting the correct pore size and optimizing conditions are vital for reliable separation in research, quality control, and therapeutic development.

Objectives and Overview

• Compare chromatographic performance of Agilent AdvanceBio SEC columns (500 Å and 1000 Å) and a competitor 1000 Å column for oligonucleotide separation.
• Use DNA and RNA ladder standards to determine exclusion limits, permeation ranges, and calibration curves.
• Assess the effect of flow rate and mobile phase composition on resolution, sensitivity, and peak shape.

Methodology

• Mobile phases evaluated: 150 mM sodium phosphate (pH 7.0); 2× PBS (~20 mM phosphate + 280 mM NaCl, pH 7.4); 50 mM potassium phosphate + 200 mM KCl (pH 7.0).
• Flow rates tested: 0.35 mL/min (standard) and 0.175 mL/min (reduced) at 30 °C.
• Injection volume: 5 µL; total run time: 30 min per injection.
• Standards: DNA ladders covering 50 bp–10 kb; RiboRuler HR RNA ladder (200 nt–6 000 nt).

Instrumentation

• Agilent 1260 Infinity II bio-inert liquid chromatography system.
• UV detector set to 260 nm.
• Columns tested:
  
  • AdvanceBio SEC 500 Å, 4.6 × 300 mm, 2.7 µm (Agilent).
  • AdvanceBio SEC 1000 Å, 4.6 × 300 mm, 2.7 µm (Agilent).
  • GTxResolve Premier SEC 1000 Å, 4.6 × 300 mm, 3 µm (Waters).

Main Results and Discussion

• Flow rate reduction to 0.175 mL/min increased peak height for large oligonucleotides without degrading resolution, due to longer detector residence and slower diffusion.
• Mobile phase comparison revealed similar retention times and peak shapes at total salt concentrations of 150–300 mM, indicating minimal secondary interactions under tested conditions.
• Calibration curves showed AdvanceBio SEC 500 Å columns resolve DNA up to ~500–1 000 bp, while 1000 Å columns extend range to ~2 000–3 000 bp.
• Single-stranded RNA ladders eluted later than size-equivalent dsDNA, reflecting a smaller hydrodynamic radius from greater conformational flexibility.

Benefits and Practical Applications

• Informed pore size selection enhances separation of oligonucleotide mixtures across a broad size range.
• Optimized flow rates boost detection sensitivity for high-molecular-weight species without lengthening analysis time.
• Robust mobile phase formulations minimize nonspecific adsorption, improving reproducibility.
• Applicable to DNA and RNA characterization in academic research, biopharmaceutical development, and QC workflows.

Future Trends and Applications

• Coupling SEC with multi-angle light scattering (MALS) for absolute molar mass determination of oligonucleotides.
• Development of tailored stationary phases for single-stranded and chemically modified oligonucleotides.
• Automation and high-throughput SEC workflows integrated into oligonucleotide manufacturing pipelines.
• Hybrid separations combining SEC with ion exchange or reverse-phase chromatography for comprehensive impurity profiling.

Conclusion

Appropriate column pore size, flow rate, and mobile phase optimization are critical for reliable SEC separation of oligonucleotides. Agilent AdvanceBio SEC 500 Å and 1000 Å columns deliver consistent performance across defined size ranges, supporting robust analytical workflows for oligonucleotide research and QC.

Reference

1. Schneider S.; Rieck F. SEC-MALS for mRNA Characterization with the Agilent 1260 Infinity II Multi-Angle Light Scattering Detector; Agilent Technologies Application Note 5994-7745EN; 2024.