Overview
Oligonucleotide purification processes frequently incorporate organic solvents such as acetonitrile (ACN) and dimethyl sulfoxide (DMSO). Selecting a tangential flow filtration (TFF) membrane that is stable under these conditions is essential for process robustness, yield, and product quality.
This application note summarizes the impact of solvent exposure on molecular weight cutoff (MWCO) for Omega™ 1 kDa and 3 kDa membranes under conditions relevant to midstream and downstream oligonucleotide processing. These Omega™ membranes are available in the Cytiva line of T-series TFF cassettes.
Key findings
- Omega membrane MWCO remains stable in DI water, 20% DMSO, and 0% to 5% ACN at pH 11.
- Both Omega 1 kDa and 3 kDa membranes show increased MWCO in 20% ACN (pH 11).
- No substantial change in MWCO for Omega 1 kDa membranes in 10% ACN (pH 11)
- Increased MWCO found for Omega 3 kDa membrane in 10% ACN (pH 11)
Introduction
Oligonucleotide manufacturing requires membrane materials that can withstand exposure to organic solvents used during cleavage and purification. Acetonitrile and DMSO are among the most common solvents in these workflows. This study evaluates the chemical robustness of Omega membranes to guide membrane selection for oligonucleotide processes.
Materials and methods
Membranes evaluated
- Omega 1 kDa (two lots, three discs per condition)
- Omega 3 kDa (two lots, three discs per condition)
Solvent exposure conditions
- Acetonitrile in ammonia solution:
0%, 5%, 10%, 20% ACN in 7 N NH₄OH (pH 11), 16 h
- DMSO: 20% DMSO in DI water, 8 h
- Control: DI water, 16 h
Testing workflow
- Membrane discs (44.5 mm) were preconditioned in DI water overnight.
- Discs were soaked in solvent under static conditions for the times described above.
- Samples were rinsed overnight with DI water to remove residual solvent.
- Mixed-dextran retention was measured using validated quality control (QC) methods.
- Membrane was assessed based on retention profile.
Fig 1. Mixed dextran MWCO ratings for (A) Omega 1 kDa and (B) Omega 3 kDa membranes after exposure to various solvents
Discussion
Oligonucleotide purification workflows frequently involve buffer exchange or desalting steps in the presence of organic solvents. The results indicate:
- Omega membranes remain well‑suited for aqueous and DMSO‑containing steps, supporting desalting, buffer exchange, and concentration operations. They also perform reliably in ACN levels up to 10% for the 1 kDa membrane, and up to 5% for the 3 kDa membrane.
- The Omega 3 kDa membrane shows vulnerability beginning at 10% ACN, and both Omega 1 kDa and 3 kDa fail at 20% ACN at pH 11, indicating that high‑ACN (> 10%) alkaline conditions should be avoided, especially for the 3 kDa MWCO membrane.
The failures observed at elevated ACN concentrations likely arise from:
- Polymer swelling or partial dissolution under strong solvent–base combinations
- Pore structure disruption, which manifests as increased MWCO (notably for the 3 kDa membrane at 10% ACN) and complete loss of integrity at 20% ACN
- MWCO drift in the 3 kDa membrane suggests earlier onset of structural perturbation compared to the 1 kDa membrane
Conclusion
This solvent‑compatibility study provides clear guidance for membrane selection in oligonucleotide purification workflows:
- Omega membranes deliver reliable performance in DI water, 20% DMSO, and low‑ACN environments at pH 11, with the 1 kDa membrane remaining stable up to 10% ACN and the 3 kDa membrane stable up to 5% ACN.
- Elevated ACN concentrations at pH 11 exceed the chemical stability limits of Omega membranes, with the 3 kDa membrane showing earlier MWCO increase at 10% ACN and both MWCO membranes failing at 20% ACN.
CY59451-07Jul26-AN