Size and Purity Assessment of Single-Guide RNAs by Anion-Exchange Chromatography (AEX)

Significance of the Topic

The quality and size integrity of single-guide RNAs (sgRNAs) are vital for the reliability of CRISPR/Cas9 gene editing. Accurate assessment of sgRNA length and purity enables consistent performance in research and therapeutic applications.

Objectives and Overview

This study demonstrates an optimized anion-exchange chromatography (AEX) method using a Protein-Pak Hi Res Q column to estimate sgRNA size and purity. A Low Range ssRNA Ladder (50–500 bases) serves as a calibration standard to determine the length of sgRNAs (100–150 mer) and evaluate sample consistency.

Methodology and Instrumentation

Methodology:

• Sample types: purified and crude HPRT sgRNA, custom GUAC ssRNA, additional sgRNAs.
• Mobile phases: 20 mM Tris pH 9.0 with TMAC gradient (0–2400 mM) for elution.
• Column conditions: Protein-Pak Hi Res Q (4.6×100 mm, 5 µm), 60 °C, flow rate 0.4 mL/min, detection at 260 nm.
• Size estimation via retention time vs. log(base number) calibration (R² = 0.993).

Instrumentation:

• ACQUITY UPLC H-Class Bio System
• ACQUITY UPLC TUV Detector (5 mm titanium cell)
• Protein-Pak Hi Res Q Column
• Empower 3 software for data acquisition

Main Results and Discussion

The optimized AEX method resolved the ssRNA ladder with clear peaks correlating with fragment size. Size estimates for five sgRNAs and one custom RNA showed < 6 % error against theoretical values. At 30 °C or using NaCl, multiple isomeric peaks appeared, underscoring the importance of TMAC and elevated temperature. Purity analysis of HPRT sgRNA revealed 88 % purity in purified samples versus 37 % in crude material, with impurities eluting earlier.

Benefits and Practical Applications

• Simultaneous size and purity assessment in a single run
• High resolution comparable to gel electrophoresis
• Quantitative and automatable protocol requiring minimal sample

Future Trends and Potential Applications

This AEX approach may extend to broader RNA analytics, quality control of gene-editing reagents, and characterization of longer or modified RNAs (50–500 bases). Integration with fraction collection could support downstream sequence analysis.

Conclusion

AEX on a Protein-Pak Hi Res Q column provides a robust, reproducible, and quantitative platform for sgRNA size and purity evaluation, critical for ensuring consistency in CRISPR/Cas9 workflows.

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