Anion exchange HPLC monitoring of mRNA in vitro transcription reactions to support mRNA manufacturing process development.

mRNA technology has recently demonstrated the ability to significantly change the timeline for developing and delivering a new vaccine from years to months. The potential of mRNA technology for rapid vaccine development has recently been highlighted by the successful development and approval of two mRNA vaccines for COVID-19. Importantly, this RNA-based approach holds promise for treatments beyond vaccines and infectious diseases, e.g., treatments for cancer, metabolic disorders, cardiovascular conditions, and autoimmune diseases. There is currently significant demand for the development of improved manufacturing processes for the production of mRNA therapeutics in an effort to increase their yield and quality. The development of suitable analytical methods for the analysis of mRNA therapeutics is critical to underpin manufacturing development and the characterisation of the drug product and drug substance. In this study we have developed a high-throughput, high-performance liquid chromatography (HPLC) workflow for the rapid analysis of mRNA generated using in vitro transcription (IVT). We have optimised anion exchange (AEX) HPLC for the analysis of mRNA directly from IVT. Chromatography was performed in under 6 min enabling separation of all of the key components in the IVT, including nucleoside triphosphates (NTPs), Cap analogue, plasmid DNA and mRNA product. Moreover, baseline separation of the NTPs was achieved, which facilitates accurate quantification of each NTP such that their consumption may be determined during IVT reactions. Furthermore, the HPLC method was used to rapidly assess the purification of the mRNA product, including removal of NTPs/Cap analogue and other contaminants after downstream purification, including solid phase extraction (SPE), oligo deoxythymidine (oligo-dT) affinity chromatography and tangential flow filtration (TFF). Using the developed method excellent precision was obtained with calibration curves for an external mRNA standard and NTPs giving correlation coefficients of 0.98 and 1.0 respectively. Intra- and inter-day studies on retention time stability of NTPs, showed a relative standard deviation ≤ 0.3% and ≤1.5% respectively. The mRNA retention time variability was ≤0.13%. This method was then utilised to monitor the progress of an IVT reaction for the production of Covid spike protein (C-Spike) mRNA to measure the increasing yield of mRNA alongside the consumption of NTPs during the reaction.

Degradation of polysorbate investigated by a high-performance liquid chromatography multi-detector system with charged aerosol and mass detection.

Polysorbate 80 is widely used as a formulation component in biopharmaceutical drug products. Recent studies have shown that polysorbate 80 is readily degraded either through direct or indirect means. The degradation of polysorbate 80 causes a concern for the long-term stability of biopharmaceutical drug product, as the breakdown products of polysorbate 80 have been shown to cause adverse effects, such as formation of sub-visible and visible particles and mAb aggregation. Understanding the path and extent of degradation is of a paramount importance for the formulator during formulation development. A multi-detector HPLC system using charged aerosol and mass detection was developed and optimized for the characterization of polysorbate 80 standards. The system included a post-column make-up flow, i.e. an inverse gradient, that enabled constant eluent composition at the detectors. The inverse gradient eliminated the main source of variability for the charged aerosol detector response, thereby enabling the calculation of the mass balance between polysorbate components with different degrees of esterification. Extracted ion chromatograms of the mass detector combined with their respective retention times were used to qualitatively characterize the polysorbate samples down to the individual components. The system was applied to study the degradation of several polysorbate standards which occurred by enzymatic digestion or long-term storage. The system provided detailed information on the mechanism of degradation without the need for additional orthogonal analytical techniques.

A Universal Eluent System for Method Scouting and Separation of Biotherapeutic Proteins by Ion-Exchange, Size-Exclusion, and Hydrophobic Interaction Chromatography.

Characterization and quality control of biotherapeutic proteins commonly require the application of several orthogonal separation techniques in order to establish product identity and purity. Many of the techniques used rely on a buffered aqueous mobile phase system to maintain the native conformation of the protein and its variants. Optimal pH, buffer substance(s), and chromatography methods vary with each protein of interest and result in tedious method development for each new drug product. Linear controlled pH gradient systems from pH 5.6 to pH 10.2 has been shown to provide a global method for the separation of charge variants of monoclonal antibodies. This can be realized using two balanced zwitterionic buffer blends. The pH linearity of the resulting system, with a cation ion exchange column in place, can generate any pH value in this accessible pH range. This study expands the scope of this buffer system and demonstrates its application in conjunction with a quaternary HPLC pump for several analytical techniques: the pH optimization of salt gradient-based anion and cation exchange during method development, as well as performing pH gradient elution. In addition, the same universal buffers are used for hydrophobic interaction and size exclusion chromatography. This eluent system omits the need to prepare different buffers for each method and flushing of the HPLC system between method changes. The implementation of this concept is further demonstrated to allow an automated method scouting approach and selection of different methods that requires minimal manual intervention.

Intact multi-attribute method (iMAM): A flexible tool for the analysis of monoclonal antibodies.

The availability of rapid methods that can accurately define and quantify biopharmaceutical critical quality attributes has been the driving force for the implementation of mass spectrometry techniques throughout the development and production pipeline. While the multi-attribute method (MAM) has become widely adopted and developed, some critical information cannot be monitored through this workflow, such as correct chain assembly or the presence of fragments or aggregates. In this study, we combine intact protein mass spectrometry and the multi-attribute method to create an intact multi-attribute method - or iMAM. Using a CFR Part 11 compliant data system, we evaluated the proposed workflow using several intact analysis approaches under both denaturing and native conditions. As for the standard MAM approach, iMAM involves the generation of an intact protein target workbook which is created from the analysis of a reference sample, with ID confirmation obtained from deconvolution results and chromatographic retention times, while quantitation is obtained from the intensities of the m/z of most abundant charge states. The created processing method is then applied to the analysis of subsequent samples. New peak detection can also be performed, monitoring the number of components revealed after each analysis. The entire data process can be automated to generate a report within the chromatography data system software. Three case studies presented herein show the potential of iMAM for implementation at different stages of the production pipeline, from product development to stability testing and batch release.

Characterization and Sequence Mapping of Large RNA and mRNA Therapeutics Using Mass Spectrometry.

Large RNA including mRNA (mRNA) has emerged as an important new class of therapeutics. Recently, this has been demonstrated by two highly efficacious vaccines based on mRNA sequences encoding for a modified version of the SARS-CoV-2 spike protein. There is currently significant demand for the development of new and improved analytical methods for the characterization of large RNA including mRNA therapeutics. In this study, we have developed an automated, high-throughput workflow for the rapid characterization and direct sequence mapping of large RNA and mRNA therapeutics. Partial RNase digestions using RNase T1 immobilized on magnetic particles were performed in conjunction with high-resolution liquid chromatography-mass spectrometry analysis. Sequence mapping was performed using automated oligoribonucleotide annotation and identifications based on MS/MS spectra. Using this approach, a >80% sequence of coverage of a range of large RNAs and mRNA therapeutics including the SARS-CoV-2 spike protein was obtained in a single analysis. The analytical workflow, including automated sample preparation, can be completed within 90 min. The ability to rapidly identify, characterize, and sequence map large mRNA therapeutics with high sequence coverage provides important information for identity testing, sequence validation, and impurity analysis.

Inline electrochemical reduction of NISTmAb for middle-up subunit liquid chromatography-mass spectrometry analysis.

Disulfide bond reduction within antibody mass spectrometry workflows is typically carried out using chemical reducing agents to produce antibody subunits for middle-down and middle-up analysis. In this contribution we offer an online electrochemical reduction method for the reduction of antibodies coupled with liquid chromatography (LC) and mass spectrometry (MS), reducing the disulfide bonds present in the antibody without the need for chemical reducing agents. An electrochemical cell placed before the analytical column and mass spectrometer facilitated complete reduction of NISTmAb inter- and intrachain disulfide bonds. Reduction and analysis were carried out under optimal solvent conditions using a trapping column and switching valve to facilitate solvent exchange during analysis. The level of reduction was shown to be affected by electrochemical potential, temperature and solvent organic content, but with optimization, complete disulfide bond cleavage was achieved. The use of an inline electrochemical cell offers a simple, rapid, workflow solution for liquid chromatography mass spectrometry analysis of antibody subunits.

Rapid Highly-Efficient Digestion and Peptide Mapping of Adeno-Associated Viruses.

Adeno-associated viruses (AAVs) comprise an area of rapidly growing interest due to their ability to act as a gene delivery vehicle in novel gene therapy strategies and vaccine development. Peptide mapping is a common technique in the biopharmaceutical industry to confirm the correct sequence, product purity, post-translational modifications (PTMs), and stability. However, conventional peptide mapping is time-consuming and has proven difficult to reproduce with viral capsids because of their high structural stability and the suboptimal localization of trypsin cleavage sites in the AAV protein sequences. In this study, we present an optimized peptide mapping-based workflow that provides thorough characterization within 1 day. This workflow is also highly reproducible due to its simplicity having very few steps and is easy to perform proteolytic digestion utilizing thermally stable pepsin, which is active at 70 °C in acidic conditions. The acidic conditions of the peptic digestions drive viral capsid denaturation and improve cleavage site accessibility. We characterized the efficiency and ease of digestion through peptide mapping of the AAV2 viral capsid protein. Using nanoflow liquid chromatography coupled with tandem mass spectrometry, we achieved 100% sequence coverage of the low-abundance VP1 capsid protein with a digestion process taking only 10 min to prepare and 45 min to complete the digestion.

Proteomic Profiling of IgG1 Producing CHO Cells Using LC/LC-SPS-MS3: The Effects of Bioprocessing Conditions on Productivity and Product Quality.

The biopharmaceutical market is dominated by monoclonal antibodies, the majority of which are produced in Chinese hamster ovary (CHO) cell lines. Intense cell engineering, in combination with optimization of various process parameters results in increasing product titers. To enable further improvements in manufacturing processes, detailed information about how certain parameters affect cellular mechanisms in the production cells, and thereby also the expressed drug substance, is required. Therefore, in this study the effects of commonly applied changes in bioprocessing parameters on an anti-IL8 IgG1 producing CHO DP-12 cell line were investigated on the level of host cell proteome expression combined with product quality assessment of the expressed IgG1 monoclonal antibody. Applying shifts in temperature, pH and dissolved oxygen concentration, respectively, resulted in altered productivity and product quality. Furthermore, analysis of the cells using two-dimensional liquid chromatography-mass spectrometry employing tandem mass tag based isotopic quantitation and synchronous precursor selection-MS3 detection revealed substantial changes in the protein expression profiles of CHO cells. Pathway analysis indicated that applied bioprocessing conditions resulted in differential activation of oxidative phosphorylation. Additionally, activation of ERK5 and TNFR1 signaling suggested an affected cell cycle. Moreover, in-depth product characterization by means of charge variant analysis, peptide mapping, as well as structural and functional analysis, revealed posttranslational and structural changes in the expressed drug substance. Taken together, the present study allows the conclusion that, in anti-IL8 IgG1 producing CHO DP-12 cells, an improved energy metabolism achieved by lowering the cell culture pH is favorable when aiming towards high antibody production rates while maintaining product quality.

Optimisation of the use of sliding window deconvolution for comprehensive characterisation of trastuzumab and adalimumab charge variants by native high resolution mass spectrometry.

The biopharmaceutical industry continues to develop mAb-based biotherapeutics in increasing numbers. Due to their complexity, there are several critical quality attributes (CQAs) that need to be measured and controlled to guarantee product safety and efficacy. Charge variant analysis is a widely used method to monitor changes in product quality during the manufacturing process of monoclonal antibodies (mAbs) and, together with a bottom-up peptide centred approach, acts as a key analytical platform to fulfil regulatory requirements. Native MS measures biomolecules under conditions that preserve most aspects of protein tertiary and quaternary structure, enabling direct characterization of large intact proteins such as mAbs. The resulting native mass spectrum of a mAb is characterized by a narrower charge-state envelope that simplifies the spectra and also condenses the ion signals into fewer peaks, increasing the signal-to-noise ratio. Algorithmic spectral deconvolution is needed for routine accurate and rapid molecular weight determination, and consequently, multiple deconvolution algorithms have evolved over the past decade. Here, we demonstrate the utility of the sliding window algorithm as a robust and powerful deconvolution tool for comprehensive characterisation of charge variant analysis data for mAbs. Optimum performance is evaluated by studying the impact of critical software parameters on detection, identification and relative quantitation of protein isoforms. By combining molecular mass and retention time information, it was possible to identify multiple modifications on adalimumab and trastuzumab, both IgG1 mAbs, including lysine truncation, deamidation and succinimide formation, along with the N-glycan distribution of each of the identified charge variants. Sliding window deconvolution also provides a key benefit of low abundant variant detection in a single analysis and the ability to detect co-eluting components with different relative abundances. The studied mAbs demonstrate the algoritms applicability for efficient data processing of both simple and complex mAbs analysed using pH gradient cation exchange chromatography coupled to native mass spectrometry.

New Insights into the Chromatography Mechanisms of Ion-Exchange Charge Variant Analysis: Dispelling Myths and Providing Guidance for Robust Method Optimization.

Charge variant analysis is a widely used analytical tool in characterization of monoclonal antibodies (mAbs). It depicts the heterogeneity of charge variant forms, some of which may differ by only minor modifications of a single amino acid. The analysis ensures product consistency with no unwanted changes to the protein. With increasing numbers of new mAb drug products emerging in the market, the need for a robust charge variant analysis has intensified. The charge variant profiles often display partially resolved peaks on shoulders of larger peaks. This puts considerably more pressure on the robustness of the method to maintain the suboptimum selectivity. New products and techniques have emerged to address these requirements, in addition to the pre-existing older methods that may not have been optimized correctly in the past. This has led to some confusion as to the best approach and strategies in optimization of charge variant analysis. We show studies from several different approaches using on-line pH monitoring to check the performance characteristics of the methods. This has led to new insights on the interactions between the protein, column, and buffer constituents. We dispel some inaccurate assumptions about the different ion-exchange elution mechanisms and suggest ways to develop high-throughput methods that remain robust and of high resolution. Streamlined automatable method development tools are presented that will result in more efficient method optimization. The mechanisms behind poor chromatography design have provided an alternative explanation behind some methods failing when in the QC laboratories.

Inter-laboratory study of an optimised peptide mapping workflow using automated trypsin digestion for monitoring monoclonal antibody product quality attributes.

Peptide mapping analysis is a regulatory expectation to verify the primary structure of a recombinant product sequence and to monitor post-translational modifications (PTMs). Although proteolytic digestion has been used for decades, it remains a labour-intensive procedure that can be challenging to accurately reproduce. Here, we describe a fast and reproducible protocol for protease digestion that is automated using immobilised trypsin on magnetic beads, which has been incorporated into an optimised peptide mapping workflow to show method transferability across laboratories. The complete workflow has the potential for use within a multi-attribute method (MAM) approach in drug development, production and QC laboratories. The sample preparation workflow is simple, ideally suited to inexperienced operators and has been extensively studied to show global applicability and robustness for mAbs by performing sample digestion and LC-MS analysis at four independent sites in Europe. LC-MS/MS along with database searching was used to characterise the protein and determine relevant product quality attributes (PQAs) for further testing. A list of relevant critical quality attributes (CQAs) was then established by creating a peptide workbook containing the specific mass-to-charge (m/z) ratios of the modified and unmodified peptides of the selected CQAs, to be monitored in a subsequent test using LC-MS analysis. Data is provided that shows robust digestion efficiency and low levels of protocol induced PTMs. Graphical abstract.

Cracking Proteoform Complexity of Ovalbumin with Anion-Exchange Chromatography-High-Resolution Mass Spectrometry under Native Conditions.

Posttranslational modifications of proteins play fundamental roles in protein function in health and disease. More than 600 different types of posttranslational modifications are known, many of them being of extremely low abundance, causing subtle changes in physicochemical properties and posing an extreme challenge to analytical methods required for their characterization. Here, we report the development of a novel pH gradient-based anion-exchange chromatography method, which can be directly interfaced to Orbitrap-based mass spectrometry for the comprehensive characterization of proteoforms at the intact protein level under native conditions. The analysis of four different proteins demonstrates outstanding chromatographic selectivity, while the mass spectra obtained are of excellent quality enabling the identification of proteoforms, including near isobaric variants, spanning 4 orders of magnitude in abundance. An in-depth analysis of ovalbumin from chicken egg white yields the identification and relative quantification of more than 150 different proteoforms, including fragmented and dimeric forms. More than 20 different ovalbumin charge variants together with their glycoform distributions are identified and quantified, many of which have not been reported previously.

Rational selection of reverse phase columns for high throughput LC-MS lipidomics.

Natural lipidomes are characterized by extremely high complexity and dynamic range of lipid concentrations. Furthermore, high diversity of lipid physicochemical properties requires high resolving powers for both chromatographic and mass spectrometric analytical platforms. Reverse-phase chromatography coupled with data-dependent MS/MS acquisition is one of the most popular techniques in untargeted lipidomics. Optimal method should provide good chromatographic separation and resolution, reproducibility, selectivity and sensitivity. Here, we developed and set-up a RPLC-MS/MS workflow capable of resolving complex mixtures of lipids in 32 min of analysis. Human blood plasma was chosen as a representative complex natural lipidome with large variance of lipid classes, species and lipid concentrations. Lipids were separated by RPLC on five different reverse phase columns with different types of stationary phase particles, size and chemistry. High mass accuracy MS analysis and data-dependent MS/MS analysis were performed using a Q Exactive™ HF Hybrid Quadrupole-Orbitrap™ Mass Spectrometer to identify individual lipid molecular species. This workflow was applied to evaluate the separation capability of each column and to identify the lipidomics profile in highly complex biological samples. As a result, we report more than 600 lipid species covering 18 lipid classes in human blood plasma and provide suggestions to the selection of the appropriate reverse phase column for the analysis of specific lipidomes.

Comprehensive characterisation of the heterogeneity of adalimumab via charge variant analysis hyphenated on-line to native high resolution Orbitrap mass spectrometry.

Charge variant analysis is a widely used tool to monitor changes in product quality during the manufacturing process of monoclonal antibodies (mAbs). Although it is a powerful technique for revealing mAb heterogeneity, an unexpected outcome, for example the appearance of previously undetected isoforms, requires further, time-consuming analysis. The process of identifying these unknowns can also result in unwanted changes to the molecule that are not attributable to the manufacturing process. To overcome this, we recently reported a method combining highly selective cation exchange chromatography-based charge variant analysis with on-line mass spectrometric (MS) detection. We further explored and adapted the chromatographic buffer system to expand the application range. Moreover, we observed no salt adducts on the native protein, also supported by the optimal choice of MS parameters, resulting in increased data quality and mass accuracy. Here, we demonstrate the utility of this improved method by performing an in-depth analysis of adalimumab before and after forced degradation. By combining molecular mass and retention time information, we were able to identify multiple modifications on adalimumab, including lysine truncation, glycation, deamidation, succinimide formation, isomerisation, N-terminal aspartic acid loss or C-terminal proline amidation and fragmentation along with the N-glycan distribution of each of these identified proteoforms. Host cell protein (HCP) analysis was performed using liquid chromatography-mass spectrometry that verified the presence of the protease Cathepsin L. Based on the presence of trace HCPs with catalytic activity, it can be questioned if fragmentation is solely driven by spontaneous hydrolysis or possibly also by enzymatic degradation.

A Novel Lipidomics Workflow for Improved Human Plasma Identification and Quantification Using RPLC-MSn Methods and Isotope Dilution Strategies.

Lipid identification and quantification are essential objectives in comprehensive lipidomics studies challenged by the high number of lipids, their chemical diversity, and their dynamic range. In this work, we developed a tailored method for profiling and quantification combining (1) isotope dilution, (2) enhanced isomer separation by C30 fused-core reversed-phase material, and (3) parallel Orbitrap and ion trap detection by the Orbitrap Fusion Lumos Tribid mass spectrometer. The combination of parallelizable ion analysis without time loss together with different fragmentation techniques (HCD/CID) and an inclusion list led to higher quality in lipid identifications exemplified in human plasma and yeast samples. Moreover, we used lipidome isotope-labeling of yeast (LILY)-a fast and efficient in vivo labeling strategy in Pichia pastoris-to produce (nonradioactive) isotopically labeled eukaryotic lipid standards in yeast. We integrated the 13C lipids in the LC-MS workflow to enable relative and absolute compound-specific quantification in yeast and human plasma samples by isotope dilution. Label-free and compound-specific quantification was validated by comparison against a recent international interlaboratory study on human plasma SRM 1950. In this way, we were able to prove that LILY enabled quantification leads to accurate results, even in complex matrices. Excellent analytical figures of merit with enhanced trueness, precision and linearity over 4-5 orders of magnitude were observed applying compound-specific quantification with 13C-labeled lipids. We strongly believe that lipidomics studies will benefit from incorporating isotope dilution and LC-MSn strategies.

Charge Variant Analysis of Monoclonal Antibodies Using Direct Coupled pH Gradient Cation Exchange Chromatography to High-Resolution Native Mass Spectrometry.

Charge variant analysis (CVA) of monoclonal antibodies (mAbs) using cation exchange chromatography is routinely used as a fingerprint of the distribution of posttranslational modifications present on the molecule. Traditional salt or pH based eluents are not suited for direct coupling to mass spectrometry due to nonvolatility or high ionic strength. This makes further analysis complicated when an alteration in the charge variant profile or the emergence of an additional peak is encountered. Here, the use of pH gradient elution using volatile, low ionic strength buffers is reported with direct coupling to high-resolution Orbitrap mass spectrometry. The development of a universal method based on pH elution was explored using a number of mAb drug products. Optimized methods facilitated the separation and identification of charge variants including individual glycoforms of the mAbs investigated using the same buffer system but with tailored gradient slopes. The developed method represents an exciting advance for the characterization of biopharmaceuticals as intact entities through the combination of native charge variant separations with high-resolution native mass spectrometry.

Generic approach to the method development of intact protein separations using hydrophobic interaction chromatography.

We describe a liquid chromatography method development approach for the separation of intact proteins using hydrophobic interaction chromatography. First, protein retention was determined as function of the salt concentration by isocratic measurements and modeled using linear regression. The error between measured and predicted retention factors was studied while varying gradient time (between 15 and 120 min) and gradient starting conditions, and ranged between 2 and 15%. To reduce the time needed to develop optimized gradient methods for hydrophobic interaction chromatography separations, retention-time estimations were also assessed based on two gradient scouting runs, resulting in significantly improved retention-time predictions (average error < 2.5%) when varying gradient time. When starting the scouting gradient at lower salt concentrations (stronger eluent), retention time prediction became inaccurate in contrast to predictions based on isocratic runs. Application of three scouting runs and a nonlinear model, incorporating the effects of gradient duration and mobile-phase composition at the start of the gradient, provides accurate results (improved fitting compared to the linear solvent-strength model) with an average error of 1.0% and maximum deviation of -8.3%. Finally, gradient scouting runs and retention-time modeling have been applied for the optimization of a critical-pair protein isoform separation encountered in a biotechnological sample.

A comprehensive study to protein retention in hydrophobic interaction chromatography.

The effect of different kosmotropic/chaotropic salt systems on retention characteristics of intact proteins has been examined in hydrophobic interaction chromatography (HIC). The performance was assessed using different column chemistries, i.e., polyalkylamide, alkylamine incorporating hydrophobic moieties, and a butyl chemistry. Selectivity in HIC is mainly governed by the salt concentration and by the molal surface tension increment of the salt. Typically, a linear relationship between the natural logarithm of the retention factor and the salt concentration is obtained. Using a 250mm long column packed with 5µm polyalkylamide functionalized silica particles and applying a 30min linear salt gradient, a peak capacity of 78 was achieved, allowing the baseline separation of seven intact proteins. The hydrophobicity index appeared to be a good indicator to predict the elution order of intact proteins in HIC mode. Furthermore, the effect of adding additives in the mobile phase, such as calcium chloride (stabilizing the 3D conformation of α-lactalbumin) and isopropanol, on retention properties has been assessed. Results indicate that HIC retention is also governed by conformational in the proteins which affect the number of accessible hydrophobic moieties.

Nucleic acid separations using superficially porous silica particles.

Ion pair reverse-phase liquid chromatography has been widely employed for nucleic acid separations. A wide range of alternative stationary phases have been utilised in conjunction with ion pair reverse-phase chromatography, including totally porous particles, non-porous particles, macroporous particles and monolithic stationary phases. In this study we have utilised superficially porous silica particles in conjunction with ion pair reverse-phase liquid chromatography for the analysis of nucleic acids. We have investigated a range of different pore-sizes and phases for the analysis of a diverse range of nucleic acids including oligonucleotides, oligoribonucleotides, phosphorothioate oligonucleotides and high molecular weight dsDNA and RNA. The pore size of the superficially porous silica particles was shown to significantly affect the resolution of the nucleic acids. Optimum separations of small oligonucleotides such as those generated in RNase mapping experiments were obtained with 80Å pore sizes and can readily be interfaced with mass spectrometry analysis. Improved resolution of larger oligonucleotides (>19mers) was observed with pore sizes of 150Å. The optimum resolution for larger dsDNA/RNA molecules was achieved using superficially porous silica particles with pore sizes of 400Å. Furthermore, we have utilised 150Å pore size solid-core particles to separate typical impurities of a fully phosphorothioated oligonucleotide, which are often generated in the synthesis of this important class of therapeutic oligonucleotide.