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

Thermo Scientific QuEChERS Sample Preparation Kits

QuEChERS is a versatile sample preparation method for analyzing pesticides, veterinary drugs, and other residues in various sample types before GC-MS or LC-MS analysis.

<div><div><div><h3>QuEChERS sample preparation—now easier, more convenient, and affordable</h3>QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe)is a sample preparation method that was initially developed in 2003 for analyzing veterinary drugs in food. The method was also tested for pesticide residue analysis in plant material with great success. In 2003, the detailed method was published in the journal AOAC International. Since then, the QuEChERS method has evolved into a sample preparation technique used on a variety of analytes in an expanding number of sample types before analysis by <a target="_blank" rel="noopener noreferrer" href="https://www.thermofisher.com/cz/en/home/industrial/mass-spectrometry/gas-chromatography-mass-spectrometry-gc-ms.html">GC-MS</a> or <a target="_blank" rel="noopener noreferrer" href="https://www.thermofisher.com/cz/en/home/industrial/mass-spectrometry/liquid-chromatography-mass-spectrometry-lc-ms.html">LC-MS</a>.Thermo Scientific QuEChERS kits contain pre-packaged, ready-weighed salts, sorbents, and buffers to streamline your workflow and minimize the potential for error. The kits are grouped according to your analytes of interest, sample matrix, and preferred QuEChERS method:<ul><li>Original 2003 Method</li><li>AOAC 2007.01 Method</li><li>EN 15662 Method</li><li>NY/T 1380-2007 Method</li></ul>Complete packages—including both extraction and clean-up kits—are available. Extraction-only and cleanup-only kits are also offered to suit your laboratory’s sample preparation needs. These pre-packaged kits save time and money, make QuEChERS procedures easier and more convenient, and ensure quality to yield reproducible results and excellent recoveries for a wide variety of analytes.<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/Thermo_Scientific_Qu_E_Ch_ERS_Sample_Preparation_Kits_2_1e99f0c81b.jpg" alt="Thermo Scientific QuEChERS Sample Preparation Kits" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_Thermo_Scientific_Qu_E_Ch_ERS_Sample_Preparation_Kits_2_1e99f0c81b.jpg 217w," sizes="100vw" width="891" height="640"><h3>Typical QuEChERS workflow</h3><div><div><div><div><div>As shown in the workflow diagram below, the QuEChERS method has four basic steps:<ol><li>Homogenize sample (fruit or vegetable)</li><li>Extract analytes of interest from a sample using extraction salts (pesticide residues, veterinary drugs, and/or mycotoxins)</li><li>Clean-up the resulting supernatant using dispersive solid phase extraction (dSPE)</li><li>Analyze by GC-MS or LC-MS</li></ol><img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/Thermo_Scientific_Qu_E_Ch_ERS_Sample_Preparation_Kits_496491ceff.jpeg" alt="Thermo Scientific QuEChERS Sample Preparation Kits" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_Thermo_Scientific_Qu_E_Ch_ERS_Sample_Preparation_Kits_496491ceff.jpeg 245w," sizes="100vw" width="1170" height="706"><div><h3>QuEChERS products</h3></div><div><h4>QuEChERS extraction kits for original 2003 method</h4></div><div>The original QuEChERS method (Anastassiades et al, 2003) was developed by Steven J. Lehotay and Michelangelo Anastassiades in 2003 for the determination of pesticide residues in fruits and vegetables. The original method was created to analyze non-base-sensitive compounds and uses a sodium chloride buffer to reduce polar interferences and enhance extraction. Buffering is an important part of the QuEChERS procedure because it allows for analysis of pesticides and other residues that display pH dependence in their recoveries, depending on the sample matrix. Three different extraction kits are available to support the original 2003 QuEChERS method.<h5>Chemicals used in the original 2003 method</h5></div><ul><li>Acetonitrile: Used to perform single-phase extraction (SPE) on a sample</li><li>Anhydrous MgSO₄: Induces phase separation between water content in sample and acetonitrile layer during liquid-liquid partitioning step; removes remaining water from sample during dispersive solid phase extraction (dSPE) step</li><li>NaCl: Induces phase separation between water content in sample and acetonitrile layer during liquid-liquid partitioning step; removes residual water from sample; reduces polar interference and enhances extraction</li><li>PSA: Primary secondary amine, used to remove polar matrix components, citric co-extractives, and free fatty acids, from sample during dispersive solid phase extraction (dSPE) step</li></ul><div><h4>QuEChERS extraction and clean-up kits for AOAC 2007.01 method</h4>The AOAC 2007.01 QuEChERS Method was developed by Steven J. Lehotay and his co-workers, who modified the original 2003 method to accommodate the use of acetate buffering at higher concentration for greater buffering strength. Buffering is an important part of the QuEChERS procedure because it allows for analysis of pesticides and other residues that display pH dependence in their recoveries, depending on the sample matrix. These extraction and clean-up products here support the AOAC 2007.01 method.<div><h5>Chemicals used in the AOAC 2007.01 method</h5><ul><li>Acetonitrile: Used to perform single-phase extraction on a sample</li><li>Anhydrous MgSO₄: Induces phase separation between water content in sample and acetonitrile layer during liquid-liquid partitioning step; removes remaining water from sample during dispersive solid phase extraction (dSPE) step</li><li>NaOAc: Buffers the sample to stabilize pH</li><li>PSA: Primary secondary amine, used to remove polar matrix components, citric co-extractives, and free fatty acids, from sample during dispersive solid phase extraction (dSPE) step</li><li>C18: Removes fats, sterols, and other non-polar interferences from sample</li><li>GCB: Graphitized carbon black, removes pigment (not recommended for use with planar pesticides)</li></ul><div><h4>QuEChERS extraction and clean-up kits for EN 15662 method</h4>The extraction and clean-up products here support the EN 15662 method. Widely used in Europe, the EN 15662 method was developed by Michelangelo Anastassiades and co-workers, who modified the original 2003 method to accommodate the use of citrate buffering at a relatively low buffering capacity. This variation uses a sodium chloride buffer to minimize polar interferences in addition to sodium citrate dihydrate and disodium citrate sesquihydrate buffers. Buffering is an important part of the QuEChERS procedure because it allows for analysis of pesticides and other residues that display pH dependence in their recoveries, depending on the sample matrix.<h5>Chemicals used in the EN 15662 method</h5><ul><li>Acetonitrile: Used to perform single-phase extraction on a sample</li><li>Anhydrous MgSO₄: Induces phase separation between water content in sample and acetonitrile layer during liquid-liquid partitioning step; removes remaining water from sample during dispersive solid phase extraction (dSPE) step</li><li>NaCl: Induces phase separation between water content in sample and acetonitrile layer during liquid-liquid partitioning step; removes residual water from sample</li><li>Trisodium Citrate: Buffers the sample to stabilize pH</li><li>Disodium Citrate Sesquihydrate: Buffers the sample to stabilize pH</li><li>PSA: Primary secondary amine, used to remove polar matrix components, citric co-extractives, and free fatty acids, from sample during dispersive solid phase extraction (dSPE) step</li><li>C18: Removes fats, sterols, and other non-polar interferences from sample</li><li>GCB: Graphitized carbon black, removes pigment (not recommended for use with planar pesticides)</li></ul><img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/Thermo_Scientific_Qu_E_Ch_ERS_Sample_Preparation_Kits_3_721562526f.jpg" alt="Thermo Scientific QuEChERS Sample Preparation Kits" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_Thermo_Scientific_Qu_E_Ch_ERS_Sample_Preparation_Kits_3_721562526f.jpg 245w," sizes="100vw" width="1471" height="488"><div><h4>QuEChERS clean-up kit for NY/T 1380-2007 method</h4></div><div>The NY/T 1380-2007 method is recommended by China Ministry of Agriculture for the QuEChERS Method sample preparation of 51 specific pesticide residues in fruits and vegetables with analysis by GC-MS.<h5>Chemicals used in the NY/T 1380-2007 method</h5><ul><li>Anhydrous MgSO₄: Induces phase separation between water content in sample and acetonitrile layer during liquid-liquid partitioning step; removes remaining water from sample during dispersive solid phase extraction (dSPE) step</li><li>PSA: Primary secondary amine, used to remove polar matrix components, citric co-extractives, and free fatty acids, from sample during dSPE step</li><li>C18: Removes fats, sterols, and other non-polar interferences from sample</li></ul></div></div></div></div></div></div></div></div></div></div></div></div>

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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