HALO Oligo C18

Importance of the topic

Separation and characterization of synthetic oligonucleotides are critical in research, therapeutic development, and quality control workflows for antisense oligos, siRNA, mRNA fragments and diagnostic probes. Fast, reproducible, and MS-compatible chromatographic methods accelerate impurity profiling, process optimization and lot release testing. Stationary phases that combine high resolution for closely related length/sequence variants with chemical stability at elevated pH and temperature provide practical advantages for routine oligonucleotide analysis.

Objectives and study overview

This application-focused document presents the HALO4 OLIGO C18 column, a Fused-Core4 (superficially porous particle, SPP) stationary phase tailored for oligonucleotide separations. The aim is to demonstrate: reproducibility across lots; chromatographic efficiency and speed for oligonucleotide ladders and mixed-sequence standards; stability under elevated pH/temperature; and capability for impurity profiling using LC/MS coupling.

Methodology

The column chemistry is a surface-modified dimethyloctadecylsilane bonded C18 on 2.7 m SPP particles with 120 c5 pores, endcapped and optimized for alkaline resistance. Typical separation conditions illustrated include ion-pair reversed-phase mobile phases (TEAA-based buffers or HFIP/TEA mixtures) with acetonitrile (and in one workflow ACN/MeOH) gradients, elevated column temperatures (50060 C) and short 2.1 x 50 mm column formats to prioritize speed and resolution. Performance tests used oligonucleotide ladders (100 to 60 mer), a commercial oligo performance mix (123 NT) and single-sequence poly dT primers to probe impurity profiles.

Used instrumentation

• Columns: HALO 120 c5 OLIGO C18, 2.7 m (various dimensions; example 2.1 x 50 mm, P/N P2A62-402).
• LC system: Shimadzu Nexera X2 (UHPLC conditions reported).
• Detectors: UV/PDA at 254 nm or 265 nm (flow cell 1 L, high data rates 40100 Hz reported).
• Mass spectrometry: high-resolution MS for impurity ID (negative ion mode, MS1 resolution ~120,000, m/z 450000). Example source settings: spray voltage ~2.5 kV, capillary ~325 C, sheath/aux/sweep gas and S-lens RF optimized for oligonucleotide detection.
• Hardware: surface-passivated column hardware to minimize stainless-steel adsorption and support bio-inert workflows.

Main results and discussion

• Separation performance: The HALO OLIGO C18 resolves single-stranded DNA ladders from 10 to 60 nucleotides with excellent peak shape and minimal tailing, enabling separations in under 3.5 minutes for a 100 mer ladder and under 4.5 minutes for mixed-sequence performance mixes.
• Lot-to-lot reproducibility: Multiple production lots showed consistent retention and chromatographic behaviour (reported RSDs <1% for tested analytes), supporting reliable column-to-column performance for system suitability and routine QC.
• Stability: Packing material demonstrated high chemical stability with less than 1% change in retention after 20,000 column volumes at elevated conditions (pH 10 and 60 C), indicating robustness for extended use under high-pH oligonucleotide conditions. Manufacturer-specified pH operating range extends to pH ~9 for routine use and temperature limits up to ~85C at high pH (lower limit 90C at low pH).
• Competitive comparison: Versus a competitor 1.7 m fully porous particle C18 (130 c5), the HALO SPP column produced sharper peaks and negligible tailing for longer oligomers (>=20 mer) while operating at substantially lower backpressure (example: HALO ~140 bar vs competitor ~255 bar under comparable flows and temperatures), enabling faster runs on standard UHPLC systems.
• Impurity profiling by LC/MS: Analysis of a 16-mer poly dT revealed minor early-eluting peaks identified by high-resolution MS as truncated sequences (n-1 to n-6) from synthesis, and a later-eluting species corresponding to a cyanoethyl-protected 16-mer. This shows the column's suitability for resolving and identifying synthetic impurities and protecting-group-related species when coupled to HRMS.

Benefits and practical applications

• High-throughput QC: Fast gradient separations and excellent resolution make the phase suitable for system suitability testing, lot release and routine impurity checks in oligonucleotide manufacturing.
• MS compatibility: Stationary phase and typical mobile phase choices (TEAA or HFIP/TEA approaches) support direct LC/MS workflows for accurate mass-based identity and impurity assignment.
• Reduced adsorption risk: Surface-passivated column hardware minimizes nonspecific adsorption of oligonucleotides, improving recovery and reproducibility, particularly for analytes prone to steel surface interactions.
• Operational efficiency: Lower system backpressures compared with some competitor columns allow rapid gradients on standard UHPLC instruments without prohibitive pressure demands.

Future trends and applications

• Growing demand for oligonucleotide therapeutics (antisense, siRNA, mRNA fragments) will increase need for high-throughput, MS-compatible QC methods; columns with SPP architectures and tailored chemistries will support these workflows.
• Alternative ion-pair-free separations, novel stationary phases designed for higher-order oligonucleotide structures, and improvements in bioinert fluidic materials will expand method options for labile or modified oligos.
• Integration with automated sample preparation and inline desalting will streamline LC/MS impurity profiling and reduce sample handling for routine testing.
• Development of larger pore SPPs or mixed-mode chemistries could extend robust separations to longer oligonucleotides and more complex constructs (conjugates, chemically modified strands).

Conclusion

The HALO OLIGO C18 column brings Fused-Core SPP advantages to oligonucleotide analysis: fast, high-resolution separations up to 60 bases, strong lot-to-lot reproducibility, chemical resilience under elevated pH/temperature, and compatibility with LC/MS. Surface-passivated hardware and moderate backpressure further support routine QC and high-throughput applications in oligonucleotide development and manufacturing.

Reference

Advanced Materials Technology. HALO OLIGO C18 product information sheet, AMT24_OLIGO_REV1. halocolumns.com. ISO 9001:2015 certified manufacturer.