Meeting EU Drinking Water Standards: The Critical Role of Sample Prep in Trace Contaminant Analysis

<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

Although modern agriculture needs to be based on accurate real-time data on soil, plant, and environmental conditions, affordable, sufficiently sensitive, and robust monitoring devices for this purpose are currently missing. According to scientists, low-cost sensors based on new smart materials and printing technologies offer a suitable solution. The results of multidisciplinary research thus far and proposals for the development of these devices have been presented by researchers from Czechia, Great Britain, Spain, and the USA in a review article in the prestigious journal <a target="_blank" rel="noopener noreferrer" href="https://www.nature.com/articles/s41467-026-68778-6#Abs1">Nature Communications</a>.“Sensor technologies for monitoring plant health are still in their infancy. Only simple sensors capable of monitoring basic parameters such as pH, soil moisture, or temperature are commonly available on the market. However, if farmers are to face current challenges, including climate change, and ensure sufficient food for humanity, they need much more effective tools that will enable them to monitor, for example, various pathogens, including bacteria and fungi. In our opinion, a suitable solution is a combination of new smart materials and printing for the production of inexpensive, durable, and scalable materials,” said the article’s first author, David Panáček from CATRIN, who worked on the study during his internship at Imperial College London.<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/CATRIN_Soucasne_senzory_nestaci_Vedci_navrhuji_novou_cestu_ke_sledovani_zdravi_rostlin_b4014952a3.jpg" alt="CATRIN: David Panáček" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_CATRIN_Soucasne_senzory_nestaci_Vedci_navrhuji_novou_cestu_ke_sledovani_zdravi_rostlin_b4014952a3.jpg 208w," sizes="100vw" width="1536" height="1152">Sensors for monitoring plant health, for example, lag behind similar devices used in human medicine. According to the authors, advances in materials science, which will enable the development of scalable sensor technologies, play a key role in this potential shift. “Printing techniques, including inkjet printing, screen printing, aerosol printing, 3D printing, and direct laser writing, offer flexible ways to produce flexible sensors, large-area sensors, and sensors integrated directly into plants. The review article summarizes recent advances in printable low-dimensional materials for agricultural sensors, analyzes their physico-chemical properties in relation to sensor performance, and discusses key challenges and future opportunities requiring interdisciplinary integration,” said one of the corresponding authors, Michal Otyepka.The research brought together materials scientists, chemists, biologists, sensing experts, and printing technology specialists. Materials research and the use of graphene-based smart materials were led by scientists from CATRIN at Palacký University and VŠB-Technical University of Ostrava. Plant biologists from CATRIN contributed their knowledge of plant development, their responses to stress conditions, and the monitoring of their properties. Researchers from Imperial College London took care of the electronics, while representatives from<a target="_blank" rel="noopener noreferrer" href="https://lcms.labrulez.com/companies/36"> CEITEC – VUT</a> focused on printing technologies. The team also included leading experts in sensing from the Catalan Institute of Nanoscience and Nanotechnology in Barcelona, and Joseph Wang of the University of California San Diego, the “father of sensing and electrochemistry,” also contributed his extensive knowledge.“This is a groundbreaking study on this topic, which has managed to attract some truly big names in their respective fields. Last but not least, the study demonstrates that interdisciplinarity at CATRIN gives rise to completely new and promising research topics, such as plant sensing and its use for studying plant-environment interactions and smart agriculture,” added another corresponding author, Nuria De Diego.

Current sensors are not good enough. Scientists propose a new way to monitor plant health

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The Czech Advanced Technology and Research Institute (CATRIN) at Palacký University is a cutting-edge scientific hub dedicated to advancing research in the fields of nanotechnology, biotechnology, and biomedicine. At its core, CATRIN boasts outstanding scientific teams, featuring international researchers. We emphasize interdisciplinarity, foster global collaborations, and work to translate our research findings into practical applications.

CATRIN

Organomation, founded in 1959, designs and manufactures high-quality nitrogen evaporators and extraction systems. Known for innovation and durability, their lab instruments are used globally for efficient sample preparation with strong customer support.

Organomation

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.

KNAUER

KNAUER Eurospher II 100 C4 (U)HPLC Columns (USP L26)

C4 stationary phases (USP L26) are often used in reversed phase mode for different application areas. 

C4 columns for Reversed Phase in HPLC and UHPLC (USP L26)C4 stationary phases (USP L26) are often used in reversed phase mode for different application areas.&nbsp;They are suitable for:<ul><li>Hydrophobic Interaction Chromatography (HIC mode)</li><li>Analysis of biomolecules like proteins and peptides</li></ul><img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/KNAUER_C4_3f3adfbdb4.webp" alt="KNAUER: C4" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_KNAUER_C4_3f3adfbdb4.webp 78w," sizes="100vw" width="200" height="400"><h3>KNAUER (U)HPLC Columns</h3>Widest range of HPLC and UHPLC columns for all separation modes and applications.<ul><li>Safe Investment: Robust and reliable columns for attractive price&nbsp;</li><li>Separation Mode: Reversed Phase, HILIC, Normale</li><li>Simplicity: Easy purchase via our online store with fast delivery</li><li>Application: All-rounder for research or highly specialised for high-throughput analysis? We have the best column for your requirements.</li><li>Flexibility: Wide selection of column and particle sizes, for (U)HPLC applications up to 1000 bar</li></ul>KNAUER offers the perfect column for any small molecule separation. No matter which separation mode, molecule and the mobile phase, we offer a suitable (U)HPLC stationary phase. Choose from a wide range of modifications, particle sizes and column dimensions to suit your application. To elongate the lifetime of your column, you can choose to use a suitable precolumn.<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/KNAUER_KNAUER_U_HPLC_C8_and_C8_A_Columns_083c60f401.webp" alt="KNAUER: KNAUER (U)HPLC Columns" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_KNAUER_KNAUER_U_HPLC_C8_and_C8_A_Columns_083c60f401.webp 182w," sizes="100vw" width="787" height="674">

KNAUER Eurosil Bioselect 300 C4 HPLC Columns (USP L26)

Eurosil Bioselect C4 has been specifically developed for the determination and purification of peptides, proteins, and oligonucleotides up to a molecular weight of approximately 100 kDa. 

Analytical wide pore phase for the determination of biomolecules bigger than 20 kDaEurosil Bioselect C4 has been specifically developed for the determination and purification of peptides, proteins, and oligonucleotides up to a molecular weight of approximately 100 kDa. The optimized manufacturing process guarantees excellent batch–to-batch reproducibility. The Eurosil Bioselect sorbent is the first choice for Biochromatography with silica material.<h5>Properties</h5><ul><li>Ultra pure, spherical wide pore HPLC phase based on wide pore silica gel</li><li>Unpolar, monomeric C4 modification, endcapped</li><li>2 % carbon content (conventional endcapping)</li><li>Separation mechanism: hydrophobic and hydrophilic interaction</li></ul><figure class="image"><img style="aspect-ratio:200/400;" src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/KNAUER_C4_3f3adfbdb4.webp" alt="KNAUER: C4" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_KNAUER_C4_3f3adfbdb4.webp 78w," sizes="100vw" width="200" height="400"></figure><h5>Recommended application areas</h5><ul><li>Hydrophilic biomolecules and especially peptides larger than 10 000- 20 000 Da</li></ul><img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/KNAUER_Eurosil_Bioselect_Phases_98acc32d0e.jpg" alt="KNAUER: Eurosil Bioselect - Phases and recommended sizes of molecules" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_KNAUER_Eurosil_Bioselect_Phases_98acc32d0e.jpg 245w," sizes="100vw" width="1385" height="778"><h3>KNAUER Wide pore HPLC columns</h3>For enhanced resolution, capacity and recovery of proteins and other biomolecules<ul><li>Material: Silica or polymer particles</li><li>Separation Ranges: 2–100 kDa</li><li>Column Brands: Eurosil Bioselect or AppliChrom®</li><li>Particle sizes: 3–10 µm</li><li>Pore Sizes: 300 or 100–1000 Å</li><li>Specific surface: 90 ± 5 m2/g</li><li>Pore volume: 0.8 ml/g</li><li>Density: 450 g/l</li><li>Applications: Peptides exceeding approximately 50 amino acids and oligonucleotides greater than 25 residues</li><li>Customize: Bioanalysis requires a lot of flexibility in the pore size, the pH range, the temperatures and the solvents used. To achieve this, we cross phase limits.</li></ul><h4>Characteristics&nbsp;</h4><ul><li>Eurosil Bioselect columns are available in 4 modifications, useful for a wide range of separation tasks involving large molecules up to 100 000 Da.</li><li>Strict manufacturing procedures ensure a very narrow pore size distribution.</li><li>Interfering anions or heavy metal ions on the silica surface are not present in Eurosil Bioselect columns because only ultra pure silica gel and high quality chemical modifications are employed.</li></ul><img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/KNAUER_Eurosil_Bioselect_85cfc2d201.jpg" alt="KNAUER: Eurosil Bioselect" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_KNAUER_Eurosil_Bioselect_85cfc2d201.jpg 222w," sizes="100vw" width="1114" height="782"><h4>Separation mechanism of Eurosil Bioselect</h4>To separate larger molecules, they need to freely access the interior of the pores of the packing material. Therefore, the analytes’ diameter must be smaller than the average pore diameter.&nbsp;For higher molecular weight solutes, the use of lower pore size materials (60-120 Å) as typically used for the analysis of small molecules may result restricted diffusion in the material´s pores and therewith reduced column efficiency.&nbsp;<h4>Modifications</h4>The recommended modification of Eurosil Bioselect depends on the molecular weight of the analytes.<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/KNAUER_Eurosil_Bioselect_chemical_modifications_1fd5d87f7b.jpg" alt="KNAUER: Eurosil Bioselect - chemical modifications" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_KNAUER_Eurosil_Bioselect_chemical_modifications_1fd5d87f7b.jpg 245w," sizes="100vw" width="955" height="505"> &nbsp;

KNAUER Eurospher II 100 C4 Prep HPLC Columns (USP L26)

C4 columns for Reversed Phase in HPLC and UHPLC (USP L26)C4 stationary phases (USP L26) are often used in reversed phase mode for different application areas.&nbsp;They are suitable for:<ul><li>Hydrophobic Interaction Chromatography (HIC mode)</li><li>Analysis of biomolecules like proteins and peptides</li></ul><img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/KNAUER_C4_3f3adfbdb4.webp" alt="KNAUER: C4" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_KNAUER_C4_3f3adfbdb4.webp 78w," sizes="100vw" width="200" height="400"><h3>KNAUER Preparative HPLC Columns</h3>The right choice for all dimensions from semi-prep to batch chromatography to SMB.<ul><li>Modifications: Reversed Phase, HILIC, Normale Phase</li><li>Max. Pressure: 400–600 bar</li><li>Column Inner Diameter (ID): 16–50 mm in our shop, more on request</li><li>Column Brands: Eurospher, Eurospher II</li><li>Safe Investment: Robustness and durability based on superior technology</li><li>Application: Easy upscaling, as all materials are available from ultra high performance to preparative scale HPLC. You can also use our upscaling calculator.</li><li>Customizable: Standard flanged hardware &amp; dAX hardware with static or dynamic axial compression available</li></ul><img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/KNAUER_Preparative_HPLC_Columns_31bc2477c3.webp" alt="KNAUER: KNAUER Preparative HPLC Columns" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_KNAUER_Preparative_HPLC_Columns_31bc2477c3.webp 221w," sizes="100vw" width="1024" height="724"><h5>Preparative HPLC columns can be offered with two different hardware types:</h5><ul><li>Versatile standard flanged hardware for nearly any application task in batch chromatography</li><li>dAX Hardware with static and dynamic axial compression for an extended lifetime and multi-column chromatography like SMB processes</li></ul>

Products from category C4 HPLC columns focused on LC columns distributed by KNAUER - page 1

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Current sensors are not good enough. Scientists propose a new way to monitor plant health

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Oligos Made Easy - Part 2: AEX