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.

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Characteristics of monoclonal antibodies (Bioanalytic)

At LabExperts, proteomic analyses are performed on a ZenoTOF 7600 high-resolution LC-MS/MS system (SCIEX). For MS/MS analyses, we use Collision induced dissociation (CID) and Electron-Activated Dissociation (EAD) fragmentation.

Antibodies are molecules made up of 4 polypeptide chains: two heavy (H - high-chain) linked to each other by a specific type of chemical bond - a disulfide bridge, and two light (L - light-chain) linked by an identical bond to the heavy chains. Monoclonal antibodies (mABs) are used in various forms - as free molecules, in the form of a drug-antibody combination, and in the form of an immunoconjugate, a drug-antibody-biopolymer combination.Their main use is in highly specific targeted therapy for cancer, cardiovascular, autoimmune and nervous system diseases. They are also used in the treatment of osteoporosis, Alzheimer's disease or transplantation. The range of applications of monoclonal antibodies is systematically expanded. The introduction of a new antibody to the market requires complex product characterization, which involves numerous proteomic analyses, which are performed by LC-MS/MS techniques, among others.<h4>LC-MS/MS</h4>The characterization of monoclonal antibodies involves many aspects, including, but not limited to, a suite of analyses related to confirmation of the structure, chain sequence and degree of modification of the antibody. Post-translational modifications (PTMs) are chemical changes that occur after the translation process. These changes generally result in an increase in the immunogenicity of the drug. For this reason, it is essential to monitor modifications as critical quality attributes (CQAs) during both the production and storage of the drug. To ensure monitoring of CQA points, the primary structure of the protein is characterized based on peptide mapping (peptide mapping) analysis. The protein under study is subjected to proteolytic digestion using enzymes such as trypsin, chymotrypsin, Lys-C, Glu-C. As a result of various proteolytic enzymes, a wide range of peptides is obtained. Ultimately, coverage of the entire sequence of the protein under study is obtained.<figure class="image"><img style="aspect-ratio:1536/947;" src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/Bioanalytic_Bioanalytic_Characteristics_of_monoclonal_antibodies_3_d94fa1623b.jpg" alt="Bioanalytic: Characteristics of monoclonal antibodies." srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_Bioanalytic_Bioanalytic_Characteristics_of_monoclonal_antibodies_3_d94fa1623b.jpg 245w," sizes="100vw" width="1536" height="947"></figure>At LabExperts, proteomic analyses are performed on a <a target="_blank" rel="noopener noreferrer" href="https://lcms.labrulez.com/library?manufacturerItems=52&amp;search=ZenoTOF+7600">ZenoTOF 7600</a> high-resolution LC-MS/MS system (SCIEX). For MS/MS analyses, we use Collision induced dissociation (CID) and Electron-Activated Dissociation (EAD) fragmentation. This provides us with data for unambiguous identification of protein-building amino acids. We process the results using Sciex OS, Skyline and Spectronaut software.<blockquote>We perform:<ul><li>Whole protein analyses - Intact - to determine the exact mass and confirm the theoretical mass;</li><li>N-glycosylation profile determination (based on MS spectrum reconstruction):<ul><li>Glycosylated form;</li><li>Deglycosylated;</li><li>Glycosylated with reduced disulfide bridges;</li><li>Deglycosylated with reduced disulfide bridges.</li></ul></li><li>Peptide maps:<ul><li>Protein digestion with various proteases so that sequence coverage is close to 100%<ul><li>Analysis of PTMs:</li><li>Location of modifications</li></ul></li><li>[%] of modifications compared to the unmodified sequence</li></ul></li><li>TiPOS testing - (technical proof of similarity) - technical confirmation of the similarity of the protein synthesized by the customer (from several LOTs) with the target protein (provided as a template).</li></ul>In order to maintain the highest possible analytical standards, we perform monoclonal antibody analyses under the regime of an internally developed and implemented laboratory quality system based on GLP principles.See also our other proteomics services: <a target="_blank" rel="noopener noreferrer" href="https://labexperts.com.pl/service/identyfikacja-bialek/">Protein identification</a>, <a target="_blank" rel="noopener noreferrer" href="https://lcms.labrulez.com/products/1294">Protein quantitative analysis</a></blockquote><img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/Bioanalytic_Bioanalytic_Characteristics_of_monoclonal_antibodies_2_cb93143fe6.jpg" alt="Bioanalytic: Bioanalytic Characteristics of monoclonal antibodies." srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_Bioanalytic_Bioanalytic_Characteristics_of_monoclonal_antibodies_2_cb93143fe6.jpg 245w," sizes="100vw" width="1536" height="908"><img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/Bioanalytic_Bioanalytic_Characteristics_of_monoclonal_antibodies_1_0e8ab7cdfa.jpg" alt="Bioanalytic: Bioanalytic Characteristics of monoclonal antibodies." srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_Bioanalytic_Bioanalytic_Characteristics_of_monoclonal_antibodies_1_0e8ab7cdfa.jpg 245w," sizes="100vw" width="1536" height="858">

Identification of the proteins (Bioanalytic)

We perform proteomic analyses on a state-of-the-art high-resolution ZenoTOF 7600 (SCIEX), in which the Zeno ion trap and EAD (Electron-Activated Dissociation) technology together make a powerful combination.

Protein identification is based on experimental measurement of peptide molecular weights and matching the amino acid sequence of the protein under study with protein sequences deposited in libraries (databases). Two approaches are most commonly used in proteomic studies: top-down and bottom-up. The top-down method involves analyzing full protein sequences. Bottom-up analyses, on the other hand, use digestion of proteins with proteolytic enzymes. The peptides obtained by digestion are analyzed using a mass spectrometer. Each analysis leads to a comparison of experimental data with data obtained by theoretical digestion of proteins described in the database.<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/Bioanalytic_Identification_of_the_proteins_Bioanalytic_2_6231b73f0d.jpg" alt="Bioanalytic: Identification of the proteins." srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_Bioanalytic_Identification_of_the_proteins_Bioanalytic_2_6231b73f0d.jpg 245w," sizes="100vw" width="1536" height="766"><h4>LC-MS/MS</h4>Tandem mass spectrometers are commonly used to determine protein sequences. They allow ion selection of pseudomolecular peptides and then fragmentation and measurement of the masses of the resulting fragments. Fragmentation using collision induced dissociation(CID ) is an invaluable tool in targeted and untargeted MS/MS analysis of small molecules. It is important to note that in proteomic analysis, data obtained using the aforementioned fragmentation method may leave gaps. For example, spectra obtained by CID fragmentation do not allow unambiguous differentiation of some amino acids: leucine from isoleucine (identical molar masses and CID fragmentation) and lysine from glutamine (very similar masses). For this reason, we perform proteomic analyses on a state-of-the-art high-resolution <a target="_blank" rel="noopener noreferrer" href="https://lcms.labrulez.com/library?manufacturerItems=52&amp;search=+ZenoTOF+7600">ZenoTOF 7600</a> (SCIEX), in which the Zeno ion trap and EAD (Electron-Activated Dissociation) technology together make a powerful combination. It enables the creation of unique fragments to differentiate problematic amino acids and increase the sensitivity and specificity of the analysis.<blockquote>We perform analyses of:<ul><li>samples from solution;</li><li>samples from a gel;</li><li>samples from a complex matrix (by prior arrangement);</li><li>samples from lyophilizer;</li><li>samples previously prepared by the client.</li></ul>Qualitative analysis of proteins includes:<ul><li>To confirm the presence of a protein, the sample is subjected to digestion and the result obtained from experimental data is compared with theoretical data;</li><li>Comparison of experimental data on the masses of peptides included in the analyzed protein with the protein sequences described in the database;</li><li>Analysis and identification of the protein mixture;</li><li>Identification of post translational modifications (PTMs) (we use the tools: Skyline, Spectronaut).</li><li>Reporting of the result including, but not limited to, confirmation of the coverage of the protein sequence obtained in the test sample with the theoretical protein and the list of modified peptides, location and % of modifications.</li></ul>Comparative analyses include:<ul><li>Determining the composition of mixtures;</li><li>Comparison and profiling of sample series - protein identification and trend analysis.</li></ul>Our offer also includes:<ul><li>Support in the planning and execution of studies (the scope is determined individually);</li><li>Assistance in the development of extraction methods from complex matrices - biological fluids, plant tissue, animal tissues (the scope is determined individually);</li><li>Statistical analysis using tools: MarkerView (PCA), GraphPad Prism, Trends, Sciex OS;</li><li><a target="_blank" rel="noopener noreferrer" href="https://lcms.labrulez.com/products/1294">Quantitative analysis of proteins</a>;</li><li><a target="_blank" rel="noopener noreferrer" href="https://lcms.labrulez.com/products/1296">Analysis and characterization of monoclonal antibodies</a>.</li></ul></blockquote><img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/Bioanalytic_Identification_of_the_proteins_Bioanalytic_1_97cf8c94b3.jpg" alt="Bioanalytic: Identification of the proteins." srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_Bioanalytic_Identification_of_the_proteins_Bioanalytic_1_97cf8c94b3.jpg 117w," sizes="100vw" width="1500" height="2000">

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Oligos Made Easy - Part 2: AEX