<h3>Charged for Action: The Hidden Secrets of AEX Oligonucleotide Analysis</h3>Oligonucleotides—short, well-defined fragments of DNA or RNA—have become indispensable tools in modern life sciences. They underpin cutting-edge applications in molecular diagnostics, gene therapy, and pharmaceutical development. Before oligonucleotides can be confidently used in research or clinical settings, however, their quality must be rigorously assessed. Purity, sequence integrity, length distribution, and chemical modifications all play a decisive role in their performance.<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/KNAUER_Oligos_Made_Easy_Part_2_AEX_2_45eee54fa0.jpg" alt="KNAUER: Oligos Made Easy - Part 2: AEX" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_KNAUER_Oligos_Made_Easy_Part_2_AEX_2_45eee54fa0.jpg 245w," sizes="100vw" width="1534" height="711">Among the analytical techniques available today, anion exchange chromatography (AEX) stands out as a robust and highly informative method for characterizing oligonucleotides. By exploiting their intrinsic negative charge, AEX provides detailed insight into product composition and impurity profiles that are difficult to obtain by other approaches.<blockquote><a target="_blank" rel="noopener noreferrer" href="https://lcms.labrulez.com/article/6808">Part 1 of the Oligos series: A Practical Guide to Oligonucleotide Production – From Concept to Final Product</a></blockquote><h4>How Scientists Read Oligonucleotides Using Charge</h4>At the core of AEX lies a simple but powerful principle: oligonucleotides carry a negatively charged phosphate backbone. This charge increases in a predictable way with strand length and, to a lesser extent, sequence composition. Anion exchange chromatography uses this property to separate oligonucleotides based on differences in charge strength and interaction with a positively charged stationary phase.As a result, AEX has become one of the most widely used analytical tools for evaluating oligonucleotide quality. It allows scientists to distinguish full-length products from truncated species, degradation products, or closely related variants—often with single-nucleotide resolution.<h4>Why Ion Exchange Works: Binding, Retention, and Release</h4>Ion exchange chromatography (IEX) relies on electrostatic interactions between analytes and a charged stationary phase. In the case of oligonucleotides, anion exchange is used, where negatively charged molecules interact with positively charged functional groups on the resin—most commonly quaternary amines.The system consists of two main components:<ul><li>Stationary phase: A positively charged resin that binds anionic analytes.</li><li>Mobile phase: An aqueous buffer system, typically combined with a salt gradient, that controls both pH and elution strength.</li></ul>Retention in AEX is governed primarily by charge. Molecules with weaker overall charge interact less strongly with the stationary phase and elute earlier, while more highly charged oligonucleotides bind more tightly and require stronger elution conditions.<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/KNAUER_Oligos_Made_Easy_Part_2_AEX_Figure_1_IEX_overview_including_elution_order_dependency_on_analyte_charge_3419ad3075.jpg" alt="KNAUER: Oligos Made Easy - Part 2 AEX: Figure 1 IEX overview including elution order dependency on analyte charge." srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_KNAUER_Oligos_Made_Easy_Part_2_AEX_Figure_1_IEX_overview_including_elution_order_dependency_on_analyte_charge_3419ad3075.jpg 245w," sizes="100vw" width="1583" height="654"><h4>The Five-Step Workflow of Ion Exchange Chromatography</h4>AEX separations generally follow a well-established sequence of steps:<ol><li>Column equilibration The column is conditioned with the starting buffer until the baseline and pH are stable. This ensures that all charged sites on the resin are ready for interaction.</li><li>Sample loading Samples, prepared in the starting buffer, are introduced under conditions that promote binding of the target oligonucleotides while minimizing retention of unwanted impurities.</li><li>Washing The column is washed with the starting buffer to remove uncharged or weakly interacting components. The baseline stabilizes as these species are flushed away.</li><li>Elution Bound oligonucleotides are released using a salt or pH gradient. Increasing ionic strength introduces competing ions that displace the analytes from the resin. Weakly bound species elute first; strongly charged oligonucleotides elute later.</li><li>Regeneration and re-equilibration A high-salt buffer removes any remaining bound material. The column is then returned to starting conditions in preparation for the next analysis.</li></ol><img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/KNAUER_Oligos_Made_Easy_Part_2_AEX_Figure_2_Five_steps_of_IEX_procedure_in_blue_outlined_using_an_example_chromatogram_in_red_38dd70b1b1.jpg" alt="KNAUER: Oligos Made Easy - Part 2 AEX: Figure 2 Five steps of IEX procedure (in blue), outlined using an example chromatogram (in red)." srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_KNAUER_Oligos_Made_Easy_Part_2_AEX_Figure_2_Five_steps_of_IEX_procedure_in_blue_outlined_using_an_example_chromatogram_in_red_38dd70b1b1.jpg 245w," sizes="100vw" width="1583" height="674"><h4>Why AEX Is Especially Effective for Oligonucleotides</h4>The repeating phosphate backbone of oligonucleotides gives rise to a strong and uniform anionic character across a wide pH range (typically pH 7–9). This makes oligonucleotides exceptionally well suited for anion exchange separations.Key factors influencing AEX behavior include:<ul><li>Charge density: Longer oligonucleotides carry more negative charges and therefore exhibit stronger retention.</li><li>Resin chemistry: Strong and weak anion exchangers differ in functional groups and pH stability, influencing selectivity and robustness.</li><li>Buffer composition: The choice of buffering ions and salt gradients directly affects elution strength and resolution.</li></ul>Salt gradients—commonly based on chloride ions—compete with the oligonucleotide backbone for binding sites on the resin. By carefully tuning gradient slope and composition, analysts can achieve highly reproducible and finely resolved separations.<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/KNAUER_Oligos_Made_Easy_Part_2_AEX_Figure_3_Ionic_interactions_and_p_H_influence_on_Anion_Exchange_Chromatography_AEX_612e231ba4.jpg" alt="KNAUER: Oligos Made Easy - Part 2 AEX: Figure 3 Ionic interactions and pH influence on Anion Exchange Chromatography (AEX)." srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_KNAUER_Oligos_Made_Easy_Part_2_AEX_Figure_3_Ionic_interactions_and_p_H_influence_on_Anion_Exchange_Chromatography_AEX_612e231ba4.jpg 245w," sizes="100vw" width="1547" height="593"><img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/KNAUER_Oligos_Made_Easy_Part_2_AEX_Figure_4_AEX_buffer_selection_and_gradient_strategy_chromatogram_with_red_buffer_gradient_curve_53fd1bb11b.jpg" alt="KNAUER: Oligos Made Easy - Part 2 AEX: Figure 4 AEX buffer selection and gradient strategy (chromatogram with red buffer gradient curve)." srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_KNAUER_Oligos_Made_Easy_Part_2_AEX_Figure_4_AEX_buffer_selection_and_gradient_strategy_chromatogram_with_red_buffer_gradient_curve_53fd1bb11b.jpg 245w," sizes="100vw" width="1600" height="327"><h4>AEX as the Gold Standard for Oligonucleotide Separation</h4>Anion exchange chromatography has become the method of choice for both analytical and preparative oligonucleotide workflows. Its advantages include:<ul><li>High resolving power: Closely related impurities, including n–1 or n–2 species, can often be separated and quantified.</li><li>Predictable retention behavior: In many cases, retention time correlates linearly with oligonucleotide length, simplifying identification.</li><li>Compatibility with modified oligonucleotides: Even chemically modified sequences retain their anionic nature, allowing AEX to resolve both products and related impurities.</li><li>Excellent control via gradient elution: Salt gradients provide precise tuning of selectivity and resolution.</li></ul>Typically, shorter or degraded oligonucleotides elute at lower ionic strength, while full-length products with higher charge density appear later in the chromatogram.<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/KNAUER_Oligos_Made_Easy_Part_2_AEX_Figure_5_AEX_Advantages_and_Challenges_7835521e34.jpg" alt="KNAUER: Oligos Made Easy - Part 2 AEX: Figure 5 AEX Advantages and Challenges." srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_KNAUER_Oligos_Made_Easy_Part_2_AEX_Figure_5_AEX_Advantages_and_Challenges_7835521e34.jpg 245w," sizes="100vw" width="1535" height="707"><h4>Final Perspective: Mastering AEX with Confidence</h4>Anion exchange chromatography may appear complex at first, but with thoughtful optimization of pH, buffer composition, and gradient conditions, it becomes a highly precise and reliable tool for oligonucleotide analysis. When properly applied, AEX delivers sharp peaks, excellent resolution, and robust performance—even for challenging sequences and modifications.For laboratories developing or refining oligonucleotide workflows, AEX offers both analytical depth and operational confidence.<blockquote>If you would like to discuss AEX method development or optimization for oligonucleotides, feel free to contact us at sales@knauer.net. More insights into practical oligonucleotide analysis will follow in our “Oligos Made Easy” series.For technical questions or in-depth discussion, the author can be reached at kindler@knauer.net</blockquote>

Oligos Made Easy - Part 2: AEX

<h3>Mastering Ion-Pair Reversed-Phase Chromatography for Oligonucleotide Analysis</h3><h4>Why Purity Is Critical in the Oligonucleotide Era</h4>Oligonucleotides — short, synthetic strands of DNA or RNA — are central to modern biotechnology. They power gene therapies, advanced diagnostics, and cutting-edge molecular research. However, before these molecules can be used in clinical or research settings, their purity and structural integrity must be thoroughly verified. High-resolution chromatographic analysis plays a crucial role in ensuring quality and safety.<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/KNAUER_Figure_1_Separation_Example_of_Oligonucleotides_5577514561.jpg" alt="KNAUER: Figure 1 - Separation Example of Oligonucleotides." srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_KNAUER_Figure_1_Separation_Example_of_Oligonucleotides_5577514561.jpg 245w," sizes="100vw" width="1024" height="368"><h4>Understanding Ion-Pair Reversed-Phase (IP-RP) Chromatography</h4>For scientists involved in oligonucleotide synthesis and characterization, Ion-Pair Reversed-Phase Chromatography (IP-RP) is one of the most effective analytical tools available.Unlike separation techniques that rely solely on charge differences, IP-RP combines:<ul><li>Ionic interactions</li><li>Hydrophobic interactions</li></ul>This dual retention mechanism enables exceptional resolution — even for oligonucleotides that differ by only a single nucleotide or subtle chemical modification. Whether assessing synthesis efficiency or purifying therapeutic-grade material, IP-RP provides reliable, reproducible separations.<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/KNAUER_Figure_2_Overview_of_IP_RP_Mode_prinicple_ecd54b6e9c.jpg" alt="KNAUER: Figure 2 - Overview of IP-RP Mode prinicple." srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_KNAUER_Figure_2_Overview_of_IP_RP_Mode_prinicple_ecd54b6e9c.jpg 245w," sizes="100vw" width="1024" height="456"><h4>The Principle Behind Ion-Pairing</h4>Oligonucleotides possess a highly negatively charged phosphate backbone. In a traditional reversed-phase system, such hydrophilic, charged molecules would show little retention.IP-RP overcomes this limitation by introducing a positively charged ion-pairing reagent into the mobile phase. The cation associates with the negatively charged oligonucleotide, forming a transient ion pair with increased hydrophobic character. This modified complex can now interact with the hydrophobic stationary phase.Retention strength depends on:<ul><li>The hydrophobicity of the ion-pair reagent</li><li>The strength of ionic interaction</li><li>The applied organic gradient</li></ul>During gradient elution (commonly using acetonitrile), analytes are released in a controlled manner according to size, sequence, and chemical modifications.<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/KNAUER_Figure_3_Ion_Pair_Reversed_Phase_Principle_9a4fcd12f2.jpg" alt="KNAUER: Figure 3 - Ion-Pair Reversed Phase Principle." srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_KNAUER_Figure_3_Ion_Pair_Reversed_Phase_Principle_9a4fcd12f2.jpg 245w," sizes="100vw" width="1024" height="393"><h4>Choosing the Right Ion-Pair Reagent</h4>Successful IP-RP separation depends heavily on selecting an appropriate ion-pair reagent. Two key factors determine retention behavior:<ol><li>Alkyl chain length</li><li>Charge density</li></ol><img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/KNAUER_Figure_4_Ion_Pair_Classification_eaad172a4e.jpg" alt="KNAUER: Figure 4 - Ion-Pair Classification." srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_KNAUER_Figure_4_Ion_Pair_Classification_eaad172a4e.jpg 245w," sizes="100vw" width="1024" height="398"><h4>Strong Cationic Ion-Pair Reagents</h4>Ion-pair reagents with longer alkyl chains provide stronger hydrophobic interactions and increased retention. A widely used example is tetrabutylammonium (TBA⁺), frequently applied for strongly retained anionic analytes.These reagents are particularly useful when high retention strength is required.<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/KNAUER_Table_1_Strong_Cationic_Ion_Pair_Reagents_8dbf00c57e.jpg" alt="KNAUER: Table 1 - Strong Cationic Ion-Pair Reagents." srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_KNAUER_Table_1_Strong_Cationic_Ion_Pair_Reagents_8dbf00c57e.jpg 245w," sizes="100vw" width="1024" height="396"><h4>Volatile (Weaker) Ion-Pair Reagents</h4>Short-chain ion-pair reagents generate weaker retention but offer a significant advantage: compatibility with LC–MS detection.Triethylammonium (TEA⁺) is among the most commonly used reagents for oligonucleotide analysis, particularly when mass spectrometric detection is involved. Other options, such as diisopropylethylammonium (DIEA⁺), are also widely applied, often combined with HFIP to enhance MS performance.<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/KNAUER_Table_2_Weak_Cationic_Ion_Pair_Reagents_6332a4975e.jpg" alt="KNAUER: Table 2 - Weak Cationic Ion-Pair Reagents." srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_KNAUER_Table_2_Weak_Cationic_Ion_Pair_Reagents_6332a4975e.jpg 245w," sizes="100vw" width="1024" height="283"><h4>Building an IP-RP Method for Oligonucleotides</h4>Developing a robust IP-RP method follows a logical sequence:<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/KNAUER_Table_3_IP_RP_Method_Step_Procedure_for_Oligos_c2216c24a0.jpg" alt="KNAUER: Table 3 - IP-RP Method Step Procedure for Oligos." srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_KNAUER_Table_3_IP_RP_Method_Step_Procedure_for_Oligos_c2216c24a0.jpg 245w," sizes="100vw" width="1024" height="304"><h5>1. Characterize the Analyte</h5>Oligonucleotides typically contain 10–50+ nucleotides and exhibit high negative charge density. This necessitates a suitable cationic partner such as TEA⁺ or DIEA⁺.<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/KNAUER_Figure_5_Cationic_Ion_Pair_Principle_for_Oligonucleotides_cb2dfb7457.jpg" alt="KNAUER: Figure 5 - Cationic Ion-Pair Principle for Oligonucleotides." srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_KNAUER_Figure_5_Cationic_Ion_Pair_Principle_for_Oligonucleotides_cb2dfb7457.jpg 245w," sizes="100vw" width="512" height="320"><h5>2. Select the Column</h5>Use a reversed-phase column with:<ul><li>Large pore size (≈300 Å)</li><li>Appropriate internal diameter</li></ul>These parameters support the so-called “ON–OFF” retention mechanism — a bind-and-elute behavior where analytes are strongly retained until the gradient triggers rapid elution.<h5>3. Optimize the Mobile Phase</h5>A typical starting condition includes:<ul><li>10 mM TEA buffer at pH ~7</li><li>Acetonitrile as organic modifier</li></ul>Gradient programs from approximately 5% to 50% organic solvent over 15–30 minutes are commonly effective for complex oligonucleotide mixtures.<h5>4. Adjust Retention Strength if Needed</h5>To increase retention:<ul><li>Raise ion-pair concentration (up to ~100 mM if required)</li><li>Select a more hydrophobic ion-pair reagent</li></ul><h5>5. Validate the Method</h5>Ensure robustness, sensitivity, and reproducibility by carefully evaluating:<ul><li>UV chromatograms</li><li>MS traces</li><li>Peak shape and resolution</li></ul><img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/KNAUER_Figure_6_UV_MS_traces_of_IP_RP_Oligonucleotide_Analysis_81faf4e9f0.jpg" alt="KNAUER: Figure 6 - UV-MS traces of IP-RP Oligonucleotide Analysis." srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_KNAUER_Figure_6_UV_MS_traces_of_IP_RP_Oligonucleotide_Analysis_81faf4e9f0.jpg 245w," sizes="100vw" width="1024" height="365"><h4>Why IP-RP Is Considered the Gold Standard</h4>Ion-Pair Reversed-Phase Chromatography uniquely combines the resolving power of reversed-phase LC with the ability to retain highly polar, charged biomolecules.Its advantages include:<ul><li>Tunable selectivity</li><li>Compatibility with UV and MS detection</li><li>Scalability from analytical to preparative workflows</li><li>Applicability from research to pharmaceutical production</li></ul>By transforming highly charged oligonucleotides into hydrophobic ion-pair complexes, IP-RP enables precise and reproducible separations that would otherwise be impossible in conventional reversed-phase systems.For these reasons, IP-RP is widely regarded as the benchmark technique for oligonucleotide analysis.<h4>Final Thoughts</h4>Mastering IP-RP is less intimidating than it may seem. A successful method comes down to:<ul><li>Selecting the right ion-pair reagent</li><li>Choosing a suitable column</li><li>Optimizing gradient conditions</li><li>Fine-tuning temperature and concentration parameters</li></ul>With thoughtful method development, IP-RP delivers sharp peaks, clean separations, and reliable performance — fully compatible with modern mass spectrometry workflows and ready to meet the demands of advanced oligonucleotide analysis.

Oligos Made Easy - Part 3: IP-RP

<h3>Why Anion Exchange Chromatography Is a Strong Choice for Large-Scale Oligonucleotide Purification</h3>Oligonucleotide therapeutics are becoming increasingly important in modern drug development. Short DNA- and RNA-based medicines are moving through clinical pipelines in growing numbers, and several have already received FDA approval. As this field expands, one question becomes increasingly important: how can these molecules be purified efficiently, reproducibly, and on a manufacturing scale?One of the most reliable answers is anion exchange chromatography (AEX).In earlier discussions, we looked at the <a target="_blank" rel="noopener noreferrer" href="https://lcms.labrulez.com/article/6846">fundamentals of oligonucleotide analysis and the core principles behind AEX separations</a>. Here, the focus shifts to preparative purification at larger scale and to the practical issues that arise when moving from laboratory development toward production. As an example, this article highlights the purification of an oligo(dT) sample on the liter scale, demonstrating how AEX can deliver both high purity and strong recovery.<h4>Why purification is so important</h4>Following chemical synthesis, crude oligonucleotide material contains a mixture of desired product, truncated sequences, and other synthesis-related impurities. For pharmaceutical use, especially in clinical and regulated settings, this crude material must be refined to a much higher purity level.Although multiple HPLC approaches are available for oligonucleotide purification, not every method is equally suitable for scale-up. Some techniques work well in analytical or small-scale formats but become less practical when transferred to larger production environments. What is needed is a purification strategy that combines high performance with straightforward scalability.<h4>What makes AEX attractive?</h4>Anion exchange chromatography has established itself as an effective purification method for oligonucleotides, especially when larger sample volumes are involved. Its main strengths include:<ul><li>High loading capacity, allowing large sample amounts to be processed efficiently</li><li>Strong separation performance, enabling high-purity product recovery</li><li>Robust scalability, from development work through to GMP-oriented production</li><li>More environmentally friendly operation, since aqueous buffer systems can be used instead of harsher organic solvents</li></ul>These features make AEX a practical option for laboratories and manufacturers seeking a reproducible purification platform that can grow with the needs of a project.<h4>Example: large-scale purification of oligo(dT)</h4>To illustrate the approach, an oligo(dT) sample was purified on the liter scale. Oligo(dT) is widely used in molecular biology, for example in mRNA isolation and as a primer in cDNA synthesis.Before chromatography, the sample required the usual preparation steps: cleavage from the solid support, deprotection with ammonia, and subsequent neutralization. The purification itself was performed on the <a target="_blank" rel="noopener noreferrer" href="https://lcms.labrulez.com/products/1621">AZURA® Prep HPLC system</a>, which is designed for high-throughput preparative workflows and offers precise gradient formation, UV detection, and automated fraction collection.<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/KNAUER_AZURA_preparative_HPLC_system_b989fe64fb.webp" alt="KNAUER: AZURA preparative HPLC system" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_KNAUER_AZURA_preparative_HPLC_system_b989fe64fb.webp 107w," sizes="100vw" width="653" height="954">The separation used a strong anion exchange resin with gradient elution based on a phosphate buffer and sodium bromide as the counterion. Sodium bromide was selected because it is less aggressive toward stainless steel components than chloride, helping protect instrument hardware during repeated operation. For optimal resolution, anion exchange particles in the 10–15 µm range are typically preferred.<h4>Performance in practice</h4>The results clearly demonstrate the suitability of AEX for oligonucleotide purification at scale.<ul><li>Purity before purification: 89%</li><li>Purity after AEX purification: 95%</li><li>Yield after purification: 90%</li></ul>These values show that the method can effectively improve product quality while maintaining a high recovery, which is a key requirement in preparative and manufacturing settings.<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/KNAUER_Chromatogram_of_oligonucleotide_purification_from_1_l_sample_a768bb4759.webp" alt="KNAUER: Chromatogram of oligonucleotide purification from 1 l sample" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_KNAUER_Chromatogram_of_oligonucleotide_purification_from_1_l_sample_a768bb4759.webp 245w," sizes="100vw" width="1920" height="848"><img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/KNAUER_Analytical_chromatogram_of_purified_and_pooled_oligo_d_T_after_AEX_0d6e5b31c5.webp" alt="KNAUER: Analytical chromatogram of purified and pooled oligo (dT) after AEX." srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_KNAUER_Analytical_chromatogram_of_purified_and_pooled_oligo_d_T_after_AEX_0d6e5b31c5.webp 240w," sizes="100vw" width="1085" height="705"><h4>Important limitations to keep in mind</h4>Like any chromatographic method, AEX also has its limitations and process considerations.<ul><li>Phosphodiester vs. phosphorothioate separations can be challenging, and resolution may decrease for longer or more heavily modified sequences.</li><li>Aggregation effects caused by secondary structures can reduce purification efficiency.</li><li>Because AEX is typically performed under aqueous conditions, there is also an increased need to monitor and control endotoxin-related process risks.</li></ul>These factors do not diminish the value of AEX, but they do underline the importance of careful method development and process control.<h4>Final thoughts</h4>For oligonucleotide-based therapeutics, purification is not just a supporting step — it is a critical part of the path from crude synthesis to clinical or commercial material. The purification strategy must be scalable, robust, and capable of consistently delivering high-quality product.Anion exchange chromatography meets many of these demands. It offers a compelling balance of purity, yield, scalability, and operational practicality, making it an important tool for both development and production environments.For teams preparing material for research, clinical studies, or GMP manufacturing, AEX on AZURA® Prep systems represents a strong and practical route toward reliable oligonucleotide purification.For additional details, the related application note “<a target="_blank" rel="noopener noreferrer" href="https://lcms.labrulez.com/labrulez-bucket-strapi-h3hsga3/VBS_0082_Large_scale_purification_of_oligonucleotides_with_ion_exchange_chromatography_5e622f1914.pdf">Oligonucleotide Purification via Ion Exchange</a>” provides more information on the method.<blockquote><ul><li>For further information on this topic, please contact the author at <a href="mailto:krop@knauer.net">krop@knauer.net</a></li><li>If you are planning to build or optimize an oligonucleotide workflow, you can also contact sales@knauer.net</li></ul></blockquote>

Oligos Made Easy - Part 7: Large Scale AEX

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Based in Berlin, KNAUER is a medium-sized, owner-managed company that has been serving the sciences since 1962. We develop and manufacture scientific instruments of superior quality for liquid chromatography, including: Analytical HPLC/UHPLC, Preparative HPLC, Fast protein liquid chromatography (FPLC), Multi-column chromatography/Simulated moving bed (SMB) chromatography. High pressure dosing, in-line detection systems, and osmometry are additional business areas.

Oligos Made Easy - Part 7: Large Scale AEX

Oligos Made Easy - Part 3: IP-RP

Oligos Made Easy - Part 2: AEX

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