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

Watrex Streamline binary gradient HPLC system

Watrex Streamline™ binary gradient HPLC system consists of two P1 pumps, static mixer, CT1 column thermostat, PDA1 diode-array detector, AS1 auto-sampler, and Clarity PDA datastation.

Streamline™ binary gradient HPLC system consists of two <a target="_blank" rel="noopener noreferrer" href="https://watrex.com/?s=streamline+p1+pump&amp;post_type=product&amp;dgwt_wcas=1?utm_source=labrulez&amp;utm_medium=propagace&amp;utm_campaign=labrulez_produkty">P1 pumps</a>, static mixer, <a target="_blank" rel="noopener noreferrer" href="https://watrex.com/obchod/chromatography/column-thermostats/streamline-ct1-columm-thermostat/?utm_source=labrulez&amp;utm_medium=propagace&amp;utm_campaign=labrulez_produkty">CT1 column thermostat</a>, <a target="_blank" rel="noopener noreferrer" href="https://watrex.com/?s=pda1&amp;post_type=product&amp;dgwt_wcas=1?utm_source=labrulez&amp;utm_medium=propagace&amp;utm_campaign=labrulez_produkty">PDA1 diode-array detector</a>, <a target="_blank" rel="noopener noreferrer" href="https://watrex.com/obchod/chromatography/sampling-devices/autosamplers/streamline-as1-autosampler/?utm_source=labrulez&amp;utm_medium=propagace&amp;utm_campaign=labrulez_produkty">AS1 auto-sampler</a>, and Clarity PDA datastation.<h3>FEATURES</h3><ul><li>Optimized pump mechanics with parallel piston design offers excellent flow rate accuracy and gradient composition at all solvents ratios</li><li>Variable volume injection range 0.1 - 999.9 μl, high precision and reproducibility, and low carryover AS1 autosapler</li><li>Excellent signal-to-noise ratio of the PDA2 detector</li><li>Data acquisition, processing and instrument control is by <a target="_blank" rel="noopener noreferrer" href="https://lcms.labrulez.com/products/999">Clarity Chromatography Station*</a></li></ul><h3>COMPONENT SPECIFICATION</h3><ul><li>Gradient solvent delivery system consisting of two P1 HPLC pumps</li></ul><h5>COMPONENT P1 HPLC pumps</h5><ul><li>Flow Rates: 0,01 ml/min – 9,99 ml/min with step 0.01 ml/min (analytical)</li><li>Flow Rates: 0,10 ml/min – 40,0 ml/min (preparative)</li><li>Pressure: 42 MPa/6000 psi (analytical, stainless steel)</li><li>Pressure: 35 Mpa/5000 psi (analytical, PEEK)</li><li>Pressure: 10 Mpa/1500 psi (preparative)</li><li>Flow precision: ± 0,2% RSD @ 1mL/min. and 1,000 psi (analytical)</li><li>Flow accuracy: ± 1% @ 1mL/min. and 1,000 psi (analytical)</li><li>Pressure accuracy: ± 2% of full-scale, with 80:20 H2O/IPA @ 1000psi</li><li>Pulsation: better than ± 0.5% @ 1mL/min. and 1,000 psi (analytical)</li><li>Remote control: USB</li><li>Remote control: Start, Stop, Status, Error</li></ul><h5>COMPONENT - PDA1 detector</h5><ul><li>Wetted Materials: Stainless Steel/ PEEK*, teflon, Glass (*depending on configuration)</li><li>Light Source: Deuterium Lamp, Tungsten Lamp</li><li>Wavelength Range: 190 – 720 nm</li><li>Number of Diodes: 256</li><li>Baseline Noise: ± 1 x 10-5 AU (@240 nm, 2 sec. risetime)</li><li>Baseline Drift: less than 3 x 10-4 AU/h</li><li>Wavelength Accuracy: 0.5 nm</li><li>Mean Pixel Pitch: 2.2 nm</li><li>Resolution: 7 nm</li><li>Linearity: higher than 2.0 AU</li><li>Data Rate: 1 Hz – 100 Hz</li></ul><h5>COMPONENT - CT1 Column thermostat</h5><ul><li>Temperature range: 10 °C above ambient temperature to 100 °C</li><li>Temperature accuracy: max. 0,5 % of actual temperature</li><li>Temperature stability: RSD &lt; 0,4 %</li><li>Settability: 0,1 °C</li><li>Internal dimensions: 320 x 50 x 30 mm (L x W x H)</li><li>Compartment material: PTFE coated metal</li><li>Compartment connection: USB</li><li>Control: build-in color touch panel, datasystem</li></ul><h5>COMPONENT - AS1 autosampler: X-Y-Z-Operation; motor driven syringe, Capacity: 60 vials, Sample Loop: standard, 20μl, Reproducibility: Fix Volume: &lt; 0.5%, Variable Volume: &lt;1.0%, Carry-over: &lt;0.01% , Programmable wash.</h5><h5>COMPONENT - Clarity™ Chromatography Station: PDA data acquisition and evaluation, gradient, and autosampler control with pre-set methods for experimental settings. PC Win 10 Professional with LCD monitor .</h5><h3>Ordering information:</h3><h5>PN/Component:</h5><ul><li>SSG101-001 Streamline™ binary HPLC system (Includes P1m+P1s pumps, PDA1 detector, CT1 thermostat, AS1 autosampler, solvent rack, Clarity PC station)</li></ul><h5>Optional configurations:</h5><ul><li>SPDA99-201 Remove PDA1 diode-array detector from system</li><li>ST99-001 Remove CT1 column thermostat from system</li><li>SAS99-001 Remove AS1 autosampler from system</li><li>SUV90-001 Add UV1 Variable UV/Vis detector to system</li><li>SFC90-001 Add FC1 Fraction collector to system</li><li>SCT90-002 Add CT1i column thermostat with manual injector from system</li></ul>

Watrex Streamline Isocratic HPLC system

Streamline™ isocratic HPLC system consists of one P1 pump, CT1i column thermostat with manual injector and UV1 UV/Vis detector.

Streamline™ isocratic HPLC system consists of one <a target="_blank" rel="noopener noreferrer" href="https://watrex.com/?s=streamline+p1+pump&amp;post_type=product&amp;dgwt_wcas=1?utm_source=labrulez&amp;utm_medium=propagace&amp;utm_campaign=labrulez_produkty">P1 pump</a>, <a target="_blank" rel="noopener noreferrer" href="https://watrex.com/obchod/chromatography/column-thermostats/streamline-ct1-columm-thermostat/?utm_source=labrulez&amp;utm_medium=propagace&amp;utm_campaign=labrulez_produkty">CT1 column thermostat </a>with manual injector and <a target="_blank" rel="noopener noreferrer" href="https://watrex.com/?s=uv1+uv&amp;post_type=product&amp;dgwt_wcas=1?utm_source=labrulez&amp;utm_medium=propagace&amp;utm_campaign=labrulez_produkty">UV1 UV/Vis detector</a>. Modular concept offers easy and economical upgrades or configuration modifications such as additional detectors, autosampler or fraction collector.<h3>FEATURES</h3><ul><li>Optimized pump mechanics with parallel piston design offers excellent flow rate accuracy and low pulsation</li><li>Excellent signal-to-noise ratio of the UV1 detector</li><li>Data acquisition, processing and instrument control is done by Clarity Chromatography Station</li></ul><h3>COMPONENT SPECIFICATION</h3><h5>SPECIFICATIONS - P1 HPLC pump:</h5><ul><li>Flow Rates: 0.001 to 10.000 mL/min</li><li>Pressure: 0 to 6,000 psi (42 MPa)</li><li>Flow precision: &gt; 0.2% RSD</li><li>Flow accuracy: ± 1 % @ 1mL/min and 7 MPa,</li><li>Pressure accuracy: ± 2% of full-scale, with 80:20 H2O/IPA @ 7 MPa</li><li>Pulsation: ± 0.5 % @ 1mL/min and 7 MPa</li><li>Remote inputs: USB</li></ul><h5>SPECIFICATIONS - UV1 UV detector:</h5><ul><li>Light Source: Deuterium Lamp, Tungsten Lamp</li><li>Wavelength Range: 190 – 800 nm</li><li>Baseline Noise: 1 x 10-5 AU (@240 nm, 2 sec. risetime)</li><li>Baseline Drift: less than 3 x 10-4 AU/h</li><li>Wavelenghth Reproducibility: ± 0.1 nm</li><li>Linearity: better than 2.5 AU</li><li>Analog Output: 1x 1 V</li></ul><h5>SPECIFICATIONS - CT1 Column thermostat:</h5><ul><li>Temperature range: 10 °C above ambient temperature to 100 °C</li><li>Temperature accuracy: max. 0,5 % of actual temperature</li><li>Temperature stability: RSD &lt; 0,4 %</li><li>Settability: 0,1 °C</li><li>Internal dimensions: 320 x 50 x 30 mm (L x W x H)</li><li>Compartment material: PTFE coated metal</li><li>Compartment connection: USB</li><li>Control: build-in color touch panel, datasystem</li></ul><h5>SPECIFICATIONS - <a target="_blank" rel="noopener noreferrer" href="https://lcms.labrulez.com/products/999">Clarity™ Chromatography Station</a>:</h5><ul><li>Advanced data acquisition and evaluation, enables routine separations with pre-set methods for experimental settings. PC Win 10 Professional with LCD monitor included</li></ul><h3>Ordering information:</h3><h5>PN/Component:</h5><ul><li>SSI101-001 Streamline™ isocratic system (Includes P1 pump,UV1 detector, CT1i column thermostat with manual injector, solvent rack, Clarity datastation)</li><li>SUV99-001 Remove UV1 detector from system</li><li>ST99-002 Remove CT1i column thermostat with manual injector from system</li><li>SPDA90-001 Add PDA1 265 photodiode detector to system</li><li>SRI90-001 Add RI1 Refractive index detector to system</li><li>SAS90-001 Add AS1 Autosampler to system</li><li>SFC90-001 Add FC1 Fraction collector to system</li></ul>

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Oligos Made Easy - Part 2: AEX