Dicationic imidazole ionic liquid stationary phase for preservative detection and its application under mixed mode of HILIC/RPLC/IEC

BACKGROUND

Food safety has always been a great concern, and the detection of additives is vital to ensuring food safety. Therefore, there is a necessity to develop a method that can quickly and efficiently separate and detect additives in food. High performance liquid chromatography is widely used in the analysis and testing of food additives. Ionic liquids have attracted wide attention in the preparation of high performance liquid chromatography stationary phases owing to their high stability, low vapor pressure and adjustable structure.

RESULTS

We developed a novel dicationic imidazole ionic liquid stationary phase for the simultaneous determination of organic preservatives (sodium benzoate, potassium sorbate) and inorganic preservatives (nitrate and nitrite) in foodstuffs under mixed-mode chromatography. The method had the advantages of easy operation, high reproducibility, good linearity and precision. In the detection of these four preservatives, the limit of detection ≤0.4740 mg⋅L-1 and the limit of quantification ≤1.5800 mg⋅L-1. The intra-day and inter-day precision were less than 4.02%, and the recovery rate was 95.90∼100.19 %. At the same time, we also characterized the stationary phase, explored the mechanism and evaluated the chromatographic performance. The stationary phase was able to operate under the mixed mode of reversed phase/hydrophilic interaction/ion exchange chromatography, and it was capable of separating hydrophilic substances, hydrophobic substances, acids, and inorganic anionic substances with good separation efficiency and had high column efficiency.

SIGNIFICANCE

In summary, the stationary phase has a promising application in the routine analysis of organic and inorganic preservatives in food. In addition, the stationary phase has good separation ability for hydrophilic, hydrophobic, ionic substances and complex samples, making it a prospective material for chromatographic separation.

Mixed-phase weak anion-exchange/reversed-phase LC-MS/MS for analysis of nucleotide sugars in human fibroblasts

Nucleotide sugars (NS) fulfil important roles in all living organisms and in humans, related defects result in severe clinical syndromes. NS can be seen as the "activated" sugars used for biosynthesis of a wide range of glycoconjugates and serve as substrates themselves for the synthesis of other nucleotide sugars. NS analysis is complicated by the presence of multiple stereoisomers without diagnostic transition ions, therefore requiring separation by liquid chromatography. In this paper, we explored weak anion-exchange/reversed-phase chromatography on a hybrid column for the separation of 17 nucleotide sugars that can occur in humans. A robust and reproducible method was established with intra- and inter-day coefficients of variation below 10% and a linear range spanning three orders of magnitude. Application to patient fibroblasts with genetic defects in mannose-1-phosphate guanylyltransferase beta, CDP-L-ribitol pyrophosphorylase A, and UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase showed abnormal levels of guanosine-5'-diphosphate-α-D-mannose (GDP-Man), cytidine-5'-diphosphate-L-ribitol (CDP-ribitol), and cytidine-5'-monophosphate-N-acetyl-β-D-neuraminic acid (CMP-Neu5Ac), respectively, in consonance with expectations based on the diagnosis. In conclusion, a novel, semi-quantitative method was established for the analysis of nucleotide sugars that can be applied to diagnose several genetic glycosylation disorders in fibroblasts and beyond.

Fabrication of ionic liquid functionalized silica with different anions and the application in mixed-mode and chiral chromatography

To realize the potential of ionic liquid functionalized silica to prepare mixed-mode and chiral stationary phases, two ionic liquid silane reagents with different anions were synthesized via a high-efficiency click reaction. Then they were decorated onto the surface of silica by a one-step bonding reaction. The functionalized silica was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and elemental analysis (EA). Two stationary phases provided satisfactory performance when compared with a commercial mixed-mode column. Notably, Sil-C10Im-D-BCS with D-3-bromocamphor-8-sulfonate (D-BCS) as anion presented chiral separation capacity towards 1,2,3,4-Tetrahydro-1-naphthol. The separation mechanism was investigated through multiple pathways, and the results revealed that the prepared stationary phases can retain and separate solutes through multiple interactions, like hydrophobic effect, ion exchange, hydrogen-bond interaction, etc. Quantum chemical calculation (QC) was employed to obtain the optimized structures and the binding energy of anions to cations. The results provided some insights into the retention mechanism from a molecular perspective. This work demonstrated the superiority of ionic liquid functionalized silica as mixed-mode stationary phases and the potential of chiral ionic liquid as chiral selectors.

Quantification of residual organic bases in an active pharmaceutical ingredient using mixed-mode chromatography and UV detection

The use of organic bases is ubiquitous in chemical synthesis, yet quantifying these compounds with traditional HPLC methodologies is often hampered by poor peak shape, low retention, and limited UV absorption. When employed in the manufacture of an active pharmaceutical ingredient (API), these compounds must be controlled to levels that are safe for human consumption, requiring robust analytical methods with sufficiently low quantification limits. This work describes the development of an HPLC method for the quantification of imidazole and 1,8-Diazabicyclo[5.4.0]undec‑7-ene (DBU) in an API using mixed-mode chromatography. Through control of the pH and organic modifier gradients, the retention of the basic analytes and API can be tuned independently to achieve desirable retention and sensitivity for each compound. The resulting HPLC method exhibits good performance in linearity, accuracy, sensitivity, specificity, and solution stability. Notably, these conditions avoid more complex detection modalities, such as mass spectrometry, while maintaining a system pressure below 400 bar, making the method compatible with a broad range of instruments. This approach to mixed-mode chromatography method development could be extended to different organic bases in the presence of complex molecules to fit the needs of projects in an academic or industrial environment.

Simultaneous determination of favipiravir and surrogates of its metabolites by means of heart-cutting bidimensional liquid chromatography (2D-LC)

Therapeutic monitoring of drugs, particularly those with multiple metabolites, can be time-consuming and labor-intensive due to the need for different analytical methods depending on the specific metabolite or matrix of interest. In this study, we employed a heart-cutting 2D-LC separation method based on the coupling of reversed-phase and mixed-mode mechanisms to determine Favipiravir and surrogates of five main metabolites. This approach was applied to serum, plasma, urine, and human peripheral blood mononuclear cells. The method underwent validation to ensure its reliability. The findings highlight the potential of 2D-LC as a practical and efficient approach for therapeutic drug monitoring.

Graft copolymerization of anion and cation onto silica and application in mixed-mode of reversed phase/ hydrophilic interaction/ ion exchange chromatography

Ionic liquids (ILs) have turned out to be one of the best choices to fabricate mixed-mode stationary phases, this work aimed to investigate the possibility and merit of copolymerizing cations and anions as modifications. We prepared two ILs stationary phases, one of which was constructed by copolymerizing cation and anion (p-vinylbenzene sulfonate). Two stationary phases were characterized and comprehensively evaluated. The stationary phases showed great repeatability (RSD <0.87%) and high efficiency (up to 83,810 plate/m). Both stationary phases can operate under a mixed mode of reversed phase/hydrophilic interaction/ion exchange chromatography (RPLC/HILIC/IEC). Chromatographic evaluation results revealed that copolymerized anions endow stationary phase superior selectivity under RPLC and HILIC modes, so hydrophobic terphenyls isomer (under ACN/H2O = 35/65) and hydrophilic nucleotides and bases (under ACN/100 mM NH4FA buffer = 90/10) are better separated. Organic and inorganic anions showed entirely different retention behaviors on two stationary phases, and the mechanism was investigated by linear solvation energy relationship (LSER) and thermodynamic analysis. This work proved that copolymerizing cations and anions of ILs could be a promising method to prepare stationary phases, the retention property and mechanism need further research.

Facile synthesis of a novel polymer/covalent organic framework@silica composite material in deep eutectic solvent for mixed-mode liquid chromatographic separation

The solvothermal synthesis of covalent organic framework (COF) modified silica gel usually requires the use of harmful organic solvents, tedious steps, and harsh reaction conditions. In pursuit of green chemistry, a new strategy for the facile preparation of COF@SiO2 composite material was realized in this work by using a low-toxicity and low-cost deep eutectic solvent as the reaction medium. Additionally, a flexible polyacrylic acid (PAA) was introduced for the purpose of improving the hydrophilic selectivity and separation efficiency of COF@SiO2. Based on the above ideas, a novel PAA/COF@SiO2 composite was successfully developed as a liquid chromatographic packing material. Performance evaluation of the slurry-packed PAA/COF@SiO2 column showed that diverse types of analytes were effectively separated, and the retention behavior of polar nucleosides showed a U-shaped trend, indicating mixed-mode of hydrophobic/hydrophilic retention mechanisms. Thermodynamic studies revealed that the separation mechanism was largely independent of temperature. This work verifies the feasibility of synthesizing polymer/COF@SiO2 composite material in the deep eutectic solvent. This strategy provides a theoretical reference for the green and facile preparation of COF@SiO2 as an efficient liquid chromatographic stationary phase.

Harnessing ceramic hydroxyapatite as an effective polishing strategy to remove product- and process-related impurities in bispecific antibody purification

Bispecific antibody (bsAb), a novel therapeutic modality, provides excellent treatment efficacy, yet poses numerous challenges to downstream process development, which are mainly due to the intricate diversity of bsAb structures and impurity profiles. Ceramic hydroxyapatite (CHT), a mixed-mode medium, allows proteins to interact with its calcium sites (C-sites) through metal affinity and/or its phosphate sites (P-sites) through cation exchange interactions. This dual-binding capability potentially offers unique bind and elute behaviours for different proteins of interest, resulting in optimal product purity when suitable elution conditions are employed. In this study, the effectiveness of CHT as a polishing step for bsAb purification was investigated across three model molecules and benchmarked against the traditional cation exchange chromatography (CEX). For both asymmetric and symmetric IgG-like bsAb post Protein A eluates, at least 97% product purity was achieved after CHT polishing. CHT delivered a superior aggregate clearance to CEX, resulting in low high molecular weight (HMW) impurities (0.5%) and low process-related impurities in the product pools. Moreover, CHT significantly mitigated "chromatography-induced aggregation" whereas eightfold more HMW was generated by CEX. This study illustrated the developability of CHT in effectively eliminating low molecular weight (LMW) impurities through post-load-wash (PLW) optimization, resulting in an additional reduction of up to 48% in LMW impurities. A mechanistic explanation regarding the performance of impurity removal and mitigation of the chromatography-induced aggregation by CHT was proposed, illustrating unique CHT capability is potentially driven by C-site cooperation, of which effectiveness could depend on the bsAb composition and size.

Polybutylene terephthalate-based stationary phase for ion-pair-free reversed-phase liquid chromatography of small interfering RNA. Part 2: Use for selective comprehensive two-dimensional liquid chromatography

With the increasing numbers of nucleic acid-based pharmaceuticals like antisense oligonucleotides (ASO), small interfering ribonucleic acid (siRNA) entering the market, research facilities, pharmaceutical industries and also regulatory authorities have been looking for efficient analytical methods for these synthetic oligonucleotides (ON). Besides of conventional one-dimensional (1D) reversed-phase liquid chromatography with or without ion-pairing (IP-RP-LC, RP-LC), hydrophilic liquid chromatography (HILIC) and mixed-mode chromatography (MMC), two-dimensional (2D) approaches combining two orthogonal chromatographic techniques also become more relevant due to the high structural complexity of oligonucleotides. Recently, we tested a polybutylene terephthalate(PBT)-based stationary phase under ion-pairing free RP mode for the liquid chromatography electrospray ionization mass spectrometry (LC-ESI-MS) analysis of siRNA (Patisiran). In this study, retention profile and chromatographic orthogonality, respectively, were compared to other LC-modes like HILIC, IP-RPLC, another ion-pair free cholesterol-bonded RPLC and MMC considering their normalized retention times. Finally, because of higher orthogonality, the ion-pairing free PBT-bonded RPLC as first dimension (¹D) was hyphenated with HILIC in the second dimension (²D) in a selective comprehensive 2D-LC setup leading to an enhanced resolution for peak purity evaluation of the main ON entities.

Investigation of several chromatographic approaches for untargeted profiling of central carbon metabolism

Monitoring the central carbon metabolism (CCM) network using liquid chromatography/mass spectrometry (LC-MS) analysis is hampered by the diverse chemical nature of its analytes, which are extremely difficult to analyze using single chromatographic conditions. Furthermore, CCM-related compounds present non-specific adsorption on metal surfaces, causing detrimental chromatographic effects and sensitivity loss. In this study, polar reversed-phase, mixed-mode (MMC), and zwitterionic hydrophilic interaction chromatography (HILIC) featuring low-adsorption hardware were investigated towards untargeted analysis of biological samples with a focus on energy metabolism-related analytes. Best results were achieved with sulfoalkylbetaine HILIC with different supports, where polymeric option featured the highest coverage and inert hybrid silica facilitated best throughput and kinetic performance at a cost of less selectivity for small carboxylic acids. MMC demonstrated excellent performance for strongly anionic analytes such as multiresidue phosphates. The obtained experimental data also suggested that an additional hydrophilic modulation might be necessary to facilitate better resolution of carboxylic acids in zHILIC mode, as found during the application of the developed method to study the effect of two different mutations on the energy metabolism of S. aureus.

Click postsynthesis of microporous organic network@silica composites for reversed-phase/hydrophilic interaction mixed-mode chromatography

Recently, the good physical and chemical properties, well-defined pore architectures, and designable topologies have made microporous organic networks (MONs) excellent potential candidates in high-performance liquid chromatography (HPLC). However, their superior hydrophobic structures restrict their application in the reversed-phase mode. To solve this obstacle and to expand the application of MONs in HPLC, we realized the thiol-yne "click" postsynthesis of a novel hydrophilic MON-2COOH@SiO₂-MER (MER denotes mercaptosuccinic acid) microsphere for reversed-phase/hydrophilic interaction mixed-mode chromatography. SiO₂ was initially decorated with MON-2COOH using 2,5-dibromoterephthalic acid and tetrakis(4-ethynylphenyl)methane as monomers, and MER was then grafted via thiol-yne click reaction to yield MON-2COOH@SiO₂-MER microspheres (5 μm) with a pore size of ~1.3 nm. The -COOH groups in 2,5-dibromoterephthalic acid and the post-modified MER molecules considerably improved the hydrophilicity of pristine MON and enhanced the hydrophilic interactions between the stationary phase and analytes. The retention mechanisms of the MON-2COOH@SiO₂-MER packed column were fully discussed with diverse hydrophobic and hydrophilic probes. Benefiting from the numerous -COOH recognition sites and benzene rings within MON-2COOH@SiO₂-MER, the packed column exhibited good resolution for the separation of sulfonamides, deoxynucleosides, alkaloids, and endocrine-disrupting chemicals. A column efficiency of 27,556 plates per meter was obtained for the separation of gastrodin. The separation performance of the MON-2COOH@SiO₂-MER packed column was also demonstrated by comparing with those of MON-2COOH@SiO₂, commercial C18, ZIC-HILIC, and bare SiO₂ columns. This work highlights the good potential of the thiol-yne click postsynthesis strategy to construct MON-based stationary phases for mixed-mode chromatography.

Application to pharmaceutical formulations

In this work, a retention behavior based on mixed-mode reversed-phase (RP)/hydrophilic interaction liquid chromatography (HILIC) was observed for benzalkonium chloride (BAK) using a core-shell column functionalized with biphenyl groups. Although in the literature, the U-shaped retention was reported for polar compounds in mixed functionalized phases, in the present work, the behavior was dependent upon the chemical structure of the analyte with mixed functionality (ammonium group, a benzyl group and an alkyl chain) and on the high selectivity of the chromatographic column. The bimodal retention was observed for the four BAK homologues using a content of acetonitrile from 65 to 95% in the mobile phase. The data were adjusted to polynomial equations which allow for modeling and predicting the U-shaped retention. The salt concentration (50 and 100 mM), anion (formate and acetate) and cation (ammonium and triethylammonium) of the salt, pH (4 and 5) in the mobile phase were studied in order to understand their influence on the two retention modes. Significant electrostatic interactions were involved in the two retention modes, especially with a content of acetonitrile higher that 90%. Linear relationships between the retention factors of the four homologues were found in a wide range of %acetonitrile when the salt and triethylamine concentration, pH and nature of salt were changed. The differences found on the retention of the homologues, when increasing the alkyl chain length, were more significant in the RP mode due to predominant hydrophobic interactions. A pH decrease and a salt concentration increase caused a retention decrease for both modes. A decrease on of the retention was observed when acetate anion was replaced by formate anion. The different order of the polynomial equations according to the used mobile phase confirmed its relevant role in the interactions with the analytes and stationary phase. A mobile phase was selected (85% acetonitrile, pH 4 and 100 mM ammonium formate) for the BAK determination in cutaneous, otic and ophthalmic formulations with different active pharmaceutical ingredients and excipients. Low sample volume (500 μL) and short analysis time (<5 min) were some of the advantages of the proposed method. In addition, good analytical performance (R² > 0.999, % RSD <4.5% for intra-day precision and <5.8% for inter-day precision, and recoveries in the 92-105% range) was obtained.

Isomer selectivity of one- and two-dimensional approaches of mixed-mode and hydrophilic interaction liquid chromatography coupled to tandem mass spectrometry for sugar phosphates of glycolysis and pentose phosphate pathways

In this study, the chromatographic behavior of mixed-mode and hydrophilic interaction liquid chromatography (HILIC) with the mixed-mode HILIC/strong anion-exchange (SAX) column HILICpak VT-50 2D and the two HILIC columns Atlantis Premier BEH Z-HILIC and Acquity Premier BEH Amide was assessed with regard to their separation capability of the metabolites from the glycolysis and pentose phosphate pathways. Chromatographic conditions were evaluated with the aim of achieving separation of the isomeric glycolytic phosphorylated carbohydrate metabolites free from isomeric interferences and thus allowing for selective targeted analysis by liquid chromatography with tandem mass spectrometry (MS/MS) using multiple reaction monitoring acquisition. The effects of pH values (8.0/9.0/10.0) of the ammonium bicarbonate buffer and gradient time were investigated during HILIC-MS/MS analysis, with the optimal conditions found at pH = 10.0. Separation of the pentose phosphate isomers (ribose 5- and 1-phosphate, xylulose 5-phosphate and ribulose 5-phosphate) was achieved on the mixed-mode HILIC/SAX (HILICpak VT-50 2D) column and HILIC BEH Amide column. Column performance was evaluated based on the direct comparison of chromatographic parameters, i.e. peak width at 50% and peak tailing factors of the individual metabolites. Parity plots were generated allowing a direct comparison between the normalized retention times and assessment of orthogonality of all 3 stationary phases evaluated. Separation of 7 biologically relevant hexose monophosphates metabolites turned out to be challenging by HILIC-MS/MS, with the BEH Amide providing the best individual results for such a separation. However, fructose 6-phosphate and glucose 1-phosphate co-eluted. Therefore, an on-line heart-cutting HILIC-Mixed Mode 2D-LC-QToF experiment was conducted, allowing the separation of this critical isomer pair. In this setup, the BEH Amide column in the ¹D separated the majority of target metabolites, while a heart-cut of the peak from totally coeluted fructose 6-phosphate and glucose 1-phosphate was separated in the ²D with HILICpak VT50-2D column, thus allowing undisturbed determination of the glycolytic phosphorylated carbohydrate metabolites due to their chromatographic separation from hexose monophosphate metabolites. The assay specificity towards 7 common hexose monophosphates was characterized (glucose 1- and 6-phosphate, galactose 1- and 6-phosphate, fructose 6-phosphate, mannose 1- and 6-phosphate). The selectivity of some rare hexose monophosphates (allose 6-phosphate, tagatose 6-phosphate, sorbose 1-phosphate) was also tested.

Mixed-Mode Chromatography and Its Role in Monoclonal Antibody Purification

As the biopharmaceutical industry matures and embraces process intensification methodologies allied to the emergence of newer personalized medicines, a key constant is the regulatory need to purify products that satisfy the criteria of safety, quality, and efficacy in each batch of released product destined for clinical use. Downstream processing operations and in particular chromatographic separations continue to play a key role in manufacturing strategies with the industry being well served by commercially available resins that provide different options to purify a particular target molecule of interest. In recent years, mixed-mode chromatography, a technique based on multimode interactions between ligands and proteins, had attracted much attention. This short review will discuss the concept and benefit of mixed-mode chromatography in purification strategies and specifically look at its application in the purification of IgG subtype monoclonal antibodies, a key product class in today's industry.

Hydroxyapatite Chromatography (HAC)

Hydroxyapatite (HA) is a mixed-mode media that has been used extensively for the purification of proteins and DNA since the 1950s. Hydroxyapatite possesses a distinctive selectivity that may be applied in the purification of a wide range of biomolecules: immunoglobulins, alkaline proteins, acidic proteins, and DNA. The functional groups of HA can both attract and repel the carboxyl and amino groups on target molecules. This unique selectivity is due to the modalities that can be employed, which are not possible with traditional anion-exchange and cation-exchange chromatography. HA is a powerful chromatography step for reducing host cell-derived impurities and aggregated product, where a 2-4 log reduction in host cell proteins, aggregates, endotoxin, and viruses are routinely achieved. This chapter describes the procedures for: efficiently packing and evaluating a HA column, purifying IgG and acidic proteins respectively using HA chromatography.

Quantifying methionine sulfoxide in therapeutic protein formulation excipients as sensitive oxidation marker

Methionine is a common excipient used in therapeutic protein liquid formulations as stabilizer and antioxidant. The oxidation of methionine to methionine sulfoxide can be regarded as a sensitive marker of oxidative stress for drug product storage conditions. In this study, a sensitive HPLC method for the quantification of methionine sulfoxide in formulated protein product was developed and qualified according to regulatory requirements using a SIELC® Primesep 100 column with UV detection. The separation involves a mixed-mode mechanism including reversed phase and cationic exchange modalities. The operating range of the method was established between 1 µM and 35 µM of methionine sulfoxide. In this testing range, the method was shown to be linear (R² > 0.99), accurate (Recovery 92.9 - 103.6%, average recovery = 99.8 ± 1.4%) and precise (intermediate precision at LoQ, CV = 2.9%). The developed test system was successfully applied to study the effects of temperature and storage conditions on methionine sulfoxide formation in complex therapeutic antibody formulations.

A clinically validated method to separate and quantify underivatized acylcarnitines and carnitine metabolic intermediates using mixed-mode chromatography with tandem mass spectrometry

Acylcarnitines are intermediate metabolites of the mitochondria that serve as biomarkers for inherited disorders of fatty acid oxidation and amino acid metabolism. The prevailing clinical method used to quantify acylcarnitines involves flow-injection tandem mass spectrometry, an approach with a number of limitations; foremost the inability to separate and therefore distinguish key isobaric acylcarnitine species. To address these issues, we report a clinically validated liquid chromatography tandem mass spectrometry method to quantify acylcarnitines, free carnitine, and carnitine metabolic intermediates in human plasma. Importantly, this method resolves clinically relevant isobaric and isomeric acylcarnitine species in a single 22 min analysis without the use of ion pairing or derivatization reagents. This unique combination of features is not achievable by existing acylcarnitine methods and is made possible by the use of a novel mixed-mode chromatographic separation. Further clinical validation studies demonstrate excellent limits of quantification, linearity, accuracy, and inter-assay precision for analyses of 38 different calibrated analytes. An additional 28 analytes are semi-quantitatively analyzed using surrogate calibrators. The study of residual patient specimens confirms the clinical utility of this method and suggests expanded applicability to the diagnosis of peroxisomal disorders. In summary, we report a clinically validated acylcarnitine method that utilizes a novel mixed-mode chromatographic separation to provide a number of advantages in terms of specificity, accuracy, sample preparation time, and clinical utility.

Purification of N-acetylgalactosamine-modified-oligonucleotides using orthogonal anion-exchange and mixed-mode chromatography approaches

N-acetylgalactosamine (GalNAc)-modified small interfering ribonucleic acids (siRNA) have shown promising outcomes for targeted siRNA delivery resulting in gene silencing in vivo; however, their structural complexity requires development of new purification methods to address high purity and recovery requirements. The current study evaluates complementary purification approaches using a mixed-mode Scherzo SS-C18 and anion-exchange (AEX) TSK-gel SuperQ-5PW for a range of single-stranded triantennary GalNAc-oligonucleotides. Initially, the semi-preparative mixed-mode support (10 × 250 mm, 3 µm) was compared against the preparative AEX analogue (21.5 × 300 mm, 13 µm), with the former affording double the recovery and higher purity of 95% over its AEX counterpart displaying 91% for a selected siRNA conjugate. An assortment of GalNAc-modified oligonucleotides was later purified using the mixed-mode resin revealing good recoveries (∼30-60%) and high purities of 90-94% ranging from straightforward to more challenging purifications. High sample loading in the 20 mg range was achieved, which was comparable with the larger preparative TSKgel SuperQ-5PW support. The Scherzo-SS-C18 resin also afforded some degree of resolution between diastereomers containing phosphorothioate functionalities. The TSKgel SuperQ-5PW support was later investigated to provide orthogonal separation selectivity to the Scherzo-SS-C18 column enabling purification of a selected, GalNAc-siRNA conjugate. The developed pH (8.5-11) and salt (0.3-0.7 M) gradients method provided enhanced separation selectivity between the free and conjugated siRNA, while minimizing formation of secondary structures and highlighting a complementary approach to deal with challenging purifications of oligonucleotide-GalNAc conjugates. Together, the use of AEX and mixed-mode columns provide much needed orthogonality to deal with complex GalNAc-modified oligonucleotides and potentially other upcoming modalities.

Synthesis of octadecylamine-derived carbon dots and application in reversed phase/hydrophilic interaction liquid chromatography

In order to make up for the deficiencies of traditional C18 column for separating strong polar compounds, combined with the good hydrophilicity of carbon dots (CDs), novel octadecylamine-derived CDs denoted as C18-CDs are designed, synthesized and applied in RPLC/HILIC mixed-mode chromatography with good separation performance towards both hydrophobic and hydrophilic compounds. C18-CDs are synthesized by simple one-step solvothermal method using octadecylamine and citric acid as carbon sources, and C18-CDs with proper polarity are collected through column chromatography purification. This C18-CDs decorated silica column showed good separation performance for polycyclic aromatic hydrocarbons and alkylbenzenes under RPLC mode. Hydrophilic compounds including sulfonamides, nucleosides and nucleobases also achieved good resolution in HILIC mode. Hydrophobic and π-π stacking interactions play major retaining roles in RPLC, whereas hydrophilic partitioning and hydrogen bond interactions turn to the main retention interactions under HILIC mode. This C18-CDs/SiO₂ column was applied for the fast detection of chloramphenicol in milk without complex sample pretreatment process. Quantitative relationship between the peak area and the concentration of chloramphenicol was established with linear equation of A = 1677c + 173. Satisfactory spiked recoveries in the range of 94.1-109.0% were obtained. This work not only proposes a simple method for improving the polarity of C18 column through forming octadecane into CDs, but also provides novel CDs with certain hydrophobicity/hydrophily suitable for mixed-mode chromatography.

Separation of vigabatrin enantiomers using mixed-mode chromatography and its application to determine the vigabatrin enantiomer levels in rat plasma

Mixed-mode chromatography-comprising a mixed phase with reversed and ionic phases, enabling hydrophobic and ion-exchange interactions simultaneously-was applied to identify vigabatrin enantiomers by HPLC with pre-column fluorescence derivatization with 2,5-dioxopyrrolidin-1-yl (4-(((2-nitrophenyl)sulfonyl)oxy)-6-(3-oxomorpholino)quinoline-2-carbonyl)prolinate (Ns-MOK-(S)-Pro-OSu). The MOK-(S)-Pro-vigabatrin enantiomers were efficiently separated within 12 min (total analysis time per sample: 28 min, including washing and equilibrium time for the column). The mobile phase was H₂O/CH₃OH/10 mM ammonium formate (pH 2.0) (20/20/60, v/v/v). Column temperature was maintained at 60℃. The proposed HPLC method could successfully monitor plasma vigabatrin enantiomer levels in rats administered (±)-vigabatrin (50 mg/kg, p.o.).

Comparing the relative robustness of anion exchange and the corresponding mixed-mode chromatography on removing a weakly-bound byproduct: A case study of bispecific antibody purification

A certain impurity may bind weaker or tighter to a particular type of chromatography column (e.g., ion exchange, hydrophobic interaction or mixed-mode) than the target protein, and this forms the basis for separation. For impurities that bind weaker, they can be removed by an appropriate pre-elution wash. However, we previously showed that wash-enabled impurity clearance is usually sensitive to loading density, causing poor robustness of the process. In this work, with a bispecific antibody case study, we compared the relative robustness of anion exchange and the corresponding mixed-mode chromatography, which mediates both anion exchange and hydrophobic interactions, on removing a weakly-bound byproduct by wash. It was learned that under a fixed appropriate wash condition, the latter achieves consistent byproduct clearance and good yield over a much wider range of loading density than the former. As wide loading density range is highly desirable for large-scale manufacturing, the above finding suggests that for a chromatography step that employs stepwise elution and relies on pre-elution wash for removing weakly-bound impurities, mixed-mode chromatography could be a better choice than the corresponding monomode ion exchange chromatography.

Removing a light-chain missing byproduct by MMC ImpRes mixed-mode chromatography under weak partitioning mode in purifying a WuXiBody-based bispecific antibody

WuXiBody is a bispecific antibody (bsAb) platform developed by WuXi Biologics. Its key feature is the replacement of one parental antibody's CH1/CL region with the T cell receptor (TCR) constant domain, a design that promotes cognate heavy chain (HC)-light chain (LC) pairing. BsAbs based on WuXiBody can adopt either asymmetric or symmetric format. For purifying a WuXiBody-based symmetric bsAb, we identified a LC-missing species as a major byproduct. While for bsAbs based on other platforms removal of such byproduct can pose considerable challenge to the downstream team, in this case WuXiBody's unique design makes separation relatively straightforward. We previously showed that Capto MMC ImpRes mixed-mode chromatography under bind-elute mode can effectively remove this LC-missing species. However, the dynamic binding capacity (DBC) of Capto MMC ImpRes is relatively low under the selected condition, making the process less desirable for large-scale manufacturing. In this study, we demonstrated that when Capto MMC ImpRes chromatography is conducted under weak partitioning mode, high throughput, good yield, and effective byproduct removal are simultaneously achieved.

Hydrophobicity of polymer based anion-exchange columns for ion chromatography

The regularities of the retention of alkanoic and alkanesulfonic acids homologues were investigated for the set of 36 anion-exchange columns produced by various manufacturers. The role of hydrophobic and electrostatic interactions in the retention and separation of organic anions was studied. The methylene selectivity increments α(CH2) were measured for the studied columns with 10 mM sodium hydroxide eluent. The influence of matrix, surface area, polar group structure, ion-exchange capacity, the density of charged functional groups on the surface and other characteristics of anion-exchangers on resin hydrophobicity was considered. A unified approach for the measurements of hydrophobic properties of anion-exchange resins is proposed and the ratio of chloride retention factor (k Cl) to α(CH2) was introduced as mixed-mode factor. The synergetic effect of electrostatic and hydrophobic interactions was observed.

Comparison of human IgG glycopeptides separation using mixed-mode hydrophilic interaction/ion-exchange liquid chromatography and reversed-phase mode

Glycoproteomics is a challenging branch of proteomics because of the micro- and macro-heterogeneity of protein glycosylation. Hydrophilic interaction liquid chromatography (HILIC) is an advantageous alternative to reversed-phase chromatography for intact glycopeptide separation prior to their identification by mass spectrometry. Nowadays, several HILIC columns differing in used chemistries are commercially available. However, there is a lack of comparative studies assessing their performance, and thus providing guidance for the selection of an adequate stationary phase for different glycoproteomics applications. Here, we compare three HILIC columns recently developed by Advanced Chromatography Technologies (ACE)- with unfunctionalized (HILIC-A), polyhydroxy functionalized (HILIC-N), and aminopropyl functionalized (HILIC-B) silica- with a C18 reversed-phase column in the separation of human immunoglobulin G glycopeptides. HILIC-A and HILIC-B exhibit mixed-mode separation combining hydrophilic and ion-exchange interactions for analyte retention. Expectably, reversed-phase mode successfully separated clusters of immunoglobulin G1 and immunoglobulin G2 glycopeptides, which differ in amino acid sequence, but was not able to adequately separate different glycoforms of the same peptide. All ACE HILIC columns showed higher separation power for different glycoforms, and we show that each column separates a different group of glycopeptides more effectively than the others. Moreover, HILIC-A and HILIC-N columns separated the isobaric A2G1F1 glycopeptides of immunoglobulin G, and thus showed the potential for the elucidation of the structure of isomeric glycoforms. Furthermore, the possible retention mechanism for the HILIC columns is discussed on the basis of the determined chromatographic parameters.

Characterization and comparison of mixed-mode and reversed-phase columns; interaction abilities and applicability for peptide separation

In this work, two mixed-mode columns from a different manufacturers and one marketed as a reversed-phase column were characterized and compared in the terms of their interaction abilities, retentivity, peak symmetry, and applicability for peptide separation. All the tested columns contain octadecyl ligand and positively charged modifier, i.e. pyridyl group for the reversed-phase column XSelect CSH C18, quaternary alkylamine for mixed-mode column Atlantis PREMIER BEH C18 AX, and permanently charged moiety (details not available from the manufacturer) for mixed-mode column Luna Omega PS C18. For detailed characterization and comparison of their interaction potential, several approaches were used. First, a simple Walters test was performed to estimate hydrophobic and silanophilic interactions of the tested columns. The highest values of both parameters were observed for column Atlantis PREMIER BEH C18 AX. To investigate the effect of pH and buffer concentration on retention, mobile phases composed of acetonitrile and buffer (ammonium formate, pH 3.0; ammonium acetate pH 4.7 and pH 6.9) in various concentrations (5mM; 10mM; 15mM and 20mM) were used. The analysis of permanently charged compounds was used to describe the electrostatic interaction abilities of the stationary phases. The most significant contribution of electrostatic interactions to the retention was observed for Atlantis PREMIER BEH C18 AX column in the mobile phase with buffer of pH 3.0. A set of ten dipeptides, three pentapeptides and one octapeptide was used to investigate the effects of pH and buffer concentration on retention and peak symmetry. Each of the tested columns provides the optimal peak shape under different buffer pH and concentration. The gradient separation of the 14 tested peptides was used to verify the application potential of the tested columns for peptide separation. The best separation was achieved within 4 minutes on column Atlantis PREMIER BEH C18 AX.

Simultaneous Quantification of Commonly Used Counter Ions in Peptides and Active Pharmaceutical Ingredients by Mixed Mode Chromatography and Evaporative Light Scattering Detection

In academia and industry, the analysis of counter ions in small molecules and synthetic peptides represents a great challenge. Due to the frequent use of salt forms and the application of a wider range of counter ions in pharmaceutically used substances, simple and generic methods for quantification are required. Especially, the analysis of trifluoracetic acid (TFA) in synthetic peptides is of high interest. Quantification of TFA is needed to assess the content and safety of synthetic peptides and for the interpretation of functional assay results, respectively. In here, a full quantitative mixed mode high performance liquid chromatography based method coupled to evaporative light scattering detection is presented. Finally, 14 positively and negatively charged counter ions were simultaneously quantified within 30 minutes. The method was validated in terms of specificity, accuracy, precision, limit of quantification, sample stability and carry over as proposed by the International Council of Harmonization. In order to prove the applicability of the procedure, small molecules reference substances and synthetic peptides were analyzed, respectively. The obtained results indicated a successful determination of counter ions in small molecules and differences to expected concentrations of prepared peptide solutions. Furthermore, an unexpectedly high content of sodium was observed for synthetic peptides.

pH-dependent selective separation of acidic and basic proteins using quaternary ammoniation functionalized cysteine-zwitterionic stationary phase with RPLC/IEC mixed-mode chromatography

In this paper, a cysteine-functionalized zwitterionic stationary phase (Cys-silica) was prepared based on the "thiol-ene" click chemistry between cysteine and vinyl-functionalized silica, and was further modified with bromoethane, 1-bromooctane and 1-bromooctadecane, respectively, to obtain a series of quaternary ammoniation-functionalized stationary phases (Cys-silica-C_n, n = 2, 8 and 18). These zwitterionic stationary phases were regarded as reversed-phase/ion-exchange (RP/IEC) mixed-mode chromatography (MMC) stationary phases for protein separation. The retention behaviors of proteins on these zwitterionic stationary phases were carefully investigated. The results indicated that the retentions of acidic and basic proteins on these zwitterinonic stationary phases were significantly influenced by the acetonitrile and salt concentrations, pH of mobile phase as well as the hydrophobicity of the ligand. The separation selectivity of proteins on these zwitterionic stationary phases strongly depended on the pH value of mobile phase. The baseline separation of 6 kinds of basic proteins can be achieved at pH 8.0 using Cys-silica-C2 or Cys-silica-C8 column, and 5 kinds of acidic proteins can also be separated completely at pH 4.0 with Cys-silica-C2 column. Moreover, owing to the quaternary ammoniation-functionalization on Cys-silica by using appropriately hydrophobic bromoalkanes, the selectivity and separation efficiency of proteins can be enhanced greatly. As a result, the acidic and basic proteins can be separated completely step by step from the complex sample by adjusting pH of mobile phase using a single Cys-silica-C2 column, which illustrates that the cysteine-functionalized zwitterionic stationary phase has a great potential for protein separation.

Benzotriazole-5-carboxylic as a mixed-mode ligand for chromatographic separation of antibody with enhanced adsorption capacity

Mixed-mode chromatography provides a promising strategy for industrial protein purification for its potential merit of balancing efficiency and cost-effectiveness. However, mixed-mode media with satisfactory selectivity and binding capacity towards antibody are still urgently needed. A new type of mixed-mode chromatography resin was prepared using benzotriazole-5-carboxylicas as ligand (BTA MM), and its application in antibody separation was explored. A typical pH-dependent protein binding was observed, and the neutral condition was favorable for antibody adsorption. Dynamic binding capacity of human immunoglobulin G (hIgG) was 57.7 mg/mL at pH 7.4 (10 mM phosphate buffer, containing 150 mM NaCl), while elution with acidic solutions (pH 3-4) could achieve a recovery of more than 85%. Protein adsorption on the resin showed a salt-independent manner, thus it could work under physiological solution conditions, with satisfied antibody selectivity. One-step purification of antibody components from human serum samples could obtain a product with the purity more than 84%. Satisfied performance was also observed when the adsorbent was used for purifying a IgG1-type monoclonal antibody (mAb) from cell culture supernatant. In addition, the benzotriazole adsorbent has been found stable enough to withstand autoclave sterilization and other harsh conditions, including 1 M NaOH, 1 M HCl, and 75% ethanol. The results proved the potential of this type of mixed-mode chromatography medium for industrial antibody purification.

Iron Oxide Nanoparticles: Multiwall Carbon Nanotube Composite Materials for Batch or Chromatographic Biomolecule Separation

Carbon-based materials are the spearhead of research in multiple fields of nanotechnology. Moreover, their role as stationary phase in chromatography is gaining relevance. We investigate a material consisting of multiwall carbon nanotubes (CNTs) and superparamagnetic iron oxide nanoparticles towards its use as a mixed-mode chromatography material. The idea is to immobilize the ion exchange material iron oxide on CNTs as a stable matrix for chromatography processes without a significant pressure drop. Iron oxide nanoparticles are synthesized and used to decorate the CNTs via a co-precipitation route. They bind to the walls of oxidized CNTs, thereby enabling to magnetically separate the composite material. This hybrid material is investigated with transmission electron microscopy, magnetometry, X-ray diffraction, X-ray photoelectron and Raman spectroscopy. Moreover, we determine its specific surface area and its wetting behavior. We also demonstrate its applicability as chromatography material for amino acid retention, describing the adsorption and desorption of different amino acids in a complex porous system surrounded by aqueous media. Thus, this material can be used as chromatographic matrix and as a magnetic batch adsorbent material due to the iron oxide nanoparticles. Our work contributes to current research on composite materials. Such materials are necessary for developing novel industrial applications or improving the performance of established processes.

Multiplexed small molecule impurity monitoring in antibody-based therapeutics by mixed-mode chromatography paired with charged aerosol detection

With advanced genetic engineering technologies and better understanding of disease biology, antibody-based therapeutics are emerging as promising new generation biopharmaceuticals. These novel antibody formats are carefully designed to possess desired features such as enhanced selectivity. However, their high level of structural complexity with multiple components often leads to long development and complex multi-step manufacturing processes, through which a variety of potential small molecule impurities can be introduced. In this work, an in-process assay was developed in which mixed-mode chromatography coupled with charged aerosol detection was utilized for multiplexed detection of nine reagents commonly used in development and manufacturing of antibody-based therapeutics: isopropyl β-d-1-thiogalactopyranoside, methionine sulfoximine, ampicillin, guanidine, dehydroascorbic acid, glutathione, tris(2-carboxyethyl)phosphine, N-acetyl cysteine, and arginine. This method utilized a mixed-mode column with ion-exchange properties operated in the hydrophilic interaction chromatography mode. Various parameters were systematically optimized and under optimal conditions, the method demonstrated excellent specificity, sensitivity, linearity, precision, accuracy, and was successfully applied to determine residual impurities in multiple samples from antibody-derived molecules.

Application of pH-salt dual gradient elution in purifying a WuXiBody-based bispecific antibody by MMC ImpRes mixed-mode chromatography

WuXiBody is a novel bispecific antibody (bsAb) platform developed by WuXi Biologics. BsAbs based on WuXiBody can adopt either asymmetric or symmetric format. In general, recombinant production of asymmetric bsAbs has a more complex impurity profile than that of symmetric ones, as assembly of the former usually involves an increased number of distinct chains. Consequently, purification of asymmetric bsAb typically poses greater challenges to the downstream team. Recently while purifying a WuXiBody-based bsAb in asymmetric format, we learned that MMC ImpRes mixed-mode chromatography under linear pH or salt gradient elution can effectively remove two out of the three low-molecular-weight byproducts post Protein A chromatography but not the third one, which was eventually removed under pH-salt dual gradient elution. This finding suggests that MMC ImpRes chromatography performed under pH-salt dual gradient elution provides better resolution than that performed under pH/salt mono gradient elution.

Data on using single- and mixed-mode resins for capture chromatography of recombinant human thioredoxin from Escherichia coli

This paper provides the data collected from screening chromatographic resins for their ability to bind and purify recombinant human thioredoxin from Escherichia coli lysate. This data was used by “Capture chromatography with mixed-mode resins: A case study with recombinant human thioredoxin from Escherichia coli” [1] to determine the optimal resin to use as a capture step to initiate downstream processing of thioredoxin. Five chromatography resins were screened using a 96-well filter plate to experiment on a wide range of pH and conductivity conditions in a shorter amount of time while saving on materials. Thioredoxin-producing E. coli was cultivated, harvested, and lysed according to Ravi et al [1]. Thioredoxin containing lysate was dialyzed into the binding conditions, pH from 5.0 to 9.0 and conductivity from 2.0 to 10.0 mS, applied to each resin and incubated with shaking for 0.5 h. Data gathered after the incubation period consisted of host cell protein and thioredoxin concentrations remaining in the supernatant, which was considered flowthrough for the remainder of this study. Samples containing high concentrations of thioredoxin after the experimental period indicate that thioredoxin did not bind to the resin at those conditions and should not be utilized as a capture step. Additionally, samples that contain low concentrations of host-cell proteins after the experimental period indicate large amounts of host-cell proteins bound to the resin. The corresponding conditions may not contribute to higher purity. Operating all screening experiments at small volumes allows for selecting optimal binding conditions while minimizing the burden on upfront biomass production.

In situ functionalization of HPLC monolithic columns based on divinylbenzene-styrene-4-vinylbenzyl chloride

The properties of chromatographic columns are largely determined by functional groups located on the sorbent surface. For monolithic columns, surface functional groups can be created during synthesis stage or by chemical bonding with the complete surface of the sorbent. One of sorbent modification approach is to use on-column click reactions with surface reactive groups. In this study, the surface treatment of monolithic sorbent based on divinylbenzene (DVB), styrene (St) and 4-vinylbenzyl chloride (4VBC) copolymer by heterocyclic nitrogen-containing compounds 1-methylimidazole (1MI), 2-methylimidazole (2MI), 2-methylpyridine (2 MP) and 4-methylpyridine (4 MP) is described. The reaction of nitrogen-containing heterocycles with chloromethyl fragments on the surface results in formation of ion pairs and significantly changes the selectivity of monolithic columns. The chromatographic properties of prepared columns are studied. Modified columns can be operated in reversed-phase (RP) chromatography or in hydrophilic interaction liquid chromatography (HILIC) with different composition of the mobile phase. Separation examples of various chemical substances classes are given.

Simultaneous quantification of polysorbate 20 and poloxamer 188 in biopharmaceutical formulations using evaporative light scattering detection

Polysorbates and Poloxamer 188 constitute the most common surfactants used in biopharmaceutical formulations owing to their excellent protein-stabilizing properties and good safety profiles. In recent years, however, a vast number of reports concerning potential risk factors closely related with their applications, such as the accumulation of degradation products, their inherent heterogeneity and adsorption effects of proteins at silicon/oil interfaces have drawn the focus to potential alternatives. Apart from tedious efforts to evaluate new excipient candidates, the use of mixed formulations leveraging combinations of well-established surfactants appears to be a promising approach to eliminate or, at least, minimize and postpone adverse effects associated with the single compounds. Due to the similar molecular properties of non-ionic surfactants, however, baseline separation of these mixtures, which is mandatory for their reliable quantification, poses a great challenge to analytical scientists. For this purpose, the present work describes the development of a robust mixed-mode liquid chromatography method coupled to evaporative light scattering detection (mixed-mode LC-ELSD) for simultaneous determination of the (intact) Polysorbate 20 and Poloxamer 188 content in biopharmaceutical formulations containing monoclonal antibodies. Extensive qualification and validation studies, comprising the evaluation of method specificity, robustness, linearity, accuracy and precision according to ICH guidelines, demonstrated its suitability for quality control studies. A case study on the storage stability of a formulated antibody was conducted to underline the method's practical utility. Finally, the versatility of the developed approach was successfully tested by quantifying Polysorbate 20-related surfactants, such as Polysorbate 80 and super-refined Polysorbate.

Purification of the human fibroblast growth factor 2 using novel animal-component free materials

This paper analyzes the use of animal-component free chromatographic materials for the efficient purification of the human fibroblast growth factor 2 (hFGF-2). hFGF-2 is produced in Escherichia coli and purified via three different chromatography steps, which include a strong cation exchange chromatography as a capture step, followed by heparin affinity chromatography and an anion exchange chromatography as a polishing step. The affinity chromatography step is based on the animal-derived material heparin. Chemically produced ligands provide a viable alternative to animal-derived components in production processes, since they are characterized by a defined structure which leads to reproducible results and a broad range of applications. The alternative ligands can be assigned to adsorber of the mixed-mode chromatography (MMC) and pseudo-affinity chromatography. Eight different animal-component free materials used as adsorbers in MMC or pseudo-affinity chromatography were tested as a substitute for heparin. The MMCs were cation exchangers characterized with further functional residues. The ligands of the pseudo-affinity chromatography were heparin-like ligands which are based on heparin's molecular structure. The alternative methods were tested as a capture step and in combination with another chromatographic step in the purification procedure of hFGF-2. In each downstream step purity, recovery and yield were analysed and compared to the conventional downstream process. Two types of MMC - the column Foresight^TM Nuvia^TM cPrime^TM from Bio-Rad Laboratories and the column HiTrap^TM Capto^TM MMC from GE Healthcare Life Sciences - can be regarded as effective animal-component free alternatives to the heparin - based adsorber.

Multiple heart-cutting mixed-mode chromatography-reversed-phase 2D-liquid chromatography method for separation and mass spectrometric characterization of synthetic oligonucleotides

Until today, ion-pair reversed-phase chromatography is still the dominating method for analytical characterization of synthetic oligonucleotides. Its hyphenation with mass spectrometry, however, has some drawbacks such as ion-suppression in electrospray ionization. To overcome this problem, we present in this work a multiple heart-cutting (MHC) two-dimensional liquid chromatography (2D-LC) method with ultra-violet (UV) and electrospray ionization (ESI) mass spectrometry (MS) detection. A reversed-phase/weak anion-exchange (RP/WAX) stationary phase in the first dimension (¹D) provides the selectivity for separation of structurally closely related oligonucleotide sequences and deletions (shortmers), respectively, using a mixed pH/triethylammonium phosphate buffer gradient at constant organic modifier content. Heart cuts of the oligonucleotide peaks are transferred to the second dimension (²D) via a multiple heart-cutting valve which is equipped with two loop decks. The ²D RP column is used for desalting via a diverter valve. Active solvent modulation enables to refocus the oligonucleotide peak into a sharp zone by ²D RP entirely free of non-volatile buffer components and ion-pair agents. Oligonucleotides can thus be sensitively detected by ESI-QTOF-MS under MS-compatible conditions.

Development of an LC-MS method for determination of nitrogen-containing heterocycles using mixed-mode liquid chromatography

N-containing heterocycles (NCHs) are largely used as precursors for pharmaceuticals and can enter the environment. Some NCHs have been shown to be toxic, persistent, and very mobile in the environment. Thus, they have received increasing attention in the past years. However, the analysis of these polar compounds in environmental samples is still a challenge for liquid chromatography. This paper investigates the use of mixed-mode liquid chromatography (MMLC), which has reversed-phase and ion exchange characteristics for measurements of NCHs in water. NCHs with low pK_a (i.e., < 2.5) display mainly reversed-phase interactions (neutral species) with the stationary phase and those with higher pK_a (i.e., > 5) interact by a mixture of reversed-phase/ion exchange/HILIC mechanism. It was also shown that the presented method performs well in the quantification of the majority of the selected NCHs in surface water with MDLs between 3 and 6 μg/L, a low matrix effect and recoveries in the range of 77–96% except for pyridazine exhibiting 32% were achieved. The method was successfully employed to follow the degradation of NCHs in ozonation.

Removal of half antibody, hole-hole homodimer and aggregates during bispecific antibody purification using MMC ImpRes mixed-mode chromatography

During recombinant production of asymmetric IgG-like bispecific antibodies (bsAbs), various by-products are often observed due to unbalanced chain expression and incorrect chain pairing. Among them, half antibody and homodimer are found with high frequency. In this work, with a case study we demonstrated that Capto MMC ImpRes mixed-mode chromatography can effectively remove these two by-products as well as antibody aggregates under optimized conditions. This makes MMC ImpRes a powerful tool for bsAb purification.

Assessment of the impact of manufacturing changes on the physicochemical properties of the recombinant vaccine carrier ExoProtein A

Efforts to develop a vaccine for the elimination of malaria include the use of carrier proteins to assemble monomeric antigens into nanoparticles to maximize immunogenicity. Recombinant ExoProtein A (EPA) is a detoxified form of Pseudomonas aeruginosa Exotoxin A which has been used as a carrier in the conjugate vaccine field. A pilot-scale process developed for purification of EPA yielded product that consistently approached a preset upper limit for host cell protein (HCP) content per human dose. To minimize the risk of bulk material exceeding the specification, the purification process was redeveloped using mixed-mode chromatography resins. Purified EPA derived from the primary and redeveloped processes were comparable following full biochemical and biophysical characterization. However, using a process specific immunoassay, the HCP content was shown to decrease from a range of 0.14-0.24% w/w of total protein to below the level of detection with the revised process. The improved process reproducibly yields EPA with highly similar quality characteristics as the original process but with an improved profile for the HCP content.

Processing of high-salt-containing protein A eluate using mixed-mode chromatography in purifying an aggregation-prone antibody

We previously developed a method that can significantly improve Protein A chromatography's capability of removing antibody aggregates. That particular method requires polyethylene glycol (PEG) and 400 mM or more of calcium chloride/sodium chloride to be added to wash and elution buffers. Consequently, Protein A chromatography performed using this method has relatively high concentration of salt in its eluate. The high salt content prevents the neutralized eluate from binding to ion exchange columns without conductivity adjustment. In the current study we demonstrated that mixed-mode chromatography can be used as a subsequent step to Protein A chromatography with high-salt-containing eluate. As mixed-mode ligand mediates salt-tolerant adsorption, it allows the neutralized Protein A eluate to be directly loaded without the need of conductivity adjustment, and thus enables a smooth and convenient connection between capture and polishing steps. In this work we also showed that the mixed-mode chromatography, performed in bind-elute mode, removed most of PEG in the Protein A eluate.

N-Propyl-N'-2-pyridylurea-modified silica as mixed-mode stationary phase with moderate weak anion exchange capacity and pH-dependent surface charge reversal

Herein, we present a novel silica-based stationary phase modified with N-propyl-N'-2-pyridylurea selector. Due to the weakly basic properties of the pyridine selector and the presence of residual silanols after selector immobilization, a zwitterionic surface with a pI observed at approximately pH 5.5 was measured by electrophoretic light scattering in pH-dependent ζ-potential determinations. The capability of the new N-propyl-N'-2-pyridylurea-modified silica to serve as mixed-mode stationary phase was investigated. For this purpose, it was characterized under RP and HILIC conditions using test mixtures. Subsequent classification of this stationary phase in comparison to in-house and commercial benchmarks was carried by principal component analysis of resultant retention factors from chromatographic tests. The results show a relatively unique mixed-mode character amongst the tested stationary phases. The chromatographic retention characteristics of acidic compounds matched well the ζ-potential determinations. The application of anion-exchange at low pH values (e.g. pH 5) and ion exclusion chromatography at pH 7 for the separation of uridine 5'-mono-, di- and triphosphate demonstrated a pH-dependent umpolung of the stationary phase surface. The combination of these separation principles in a pH gradient from 5 to 7 gave rise to weak anion-exchange selectivity with a charge-inducted elution due to repulsive interactions at higher pH and resulted in a significant faster separation with improved peak shape under mild elution conditions.

Isoform Separation by a Mixed-mode Resin, TOYOPEARL MX-Trp-650M

TOYOPEARL particles are cross-linked hydroxylated methacrylic polymers available in different pore and particle sizes. They are conjugated with different ligands to generate ion-exchange, hydrophobic interaction and affinity resins. They have excellent physical and chemical properties. A mixed-mode resin, TOYOPEARL MX-Trp-650M, is made of this particle with tryptophan conjugated via N-terminal amino group and hence has both hydrophobic/aromatic side chain and carboxyl group. In this review, I will summarize the properties of the TOYOPEARL particles and MX-Trp-650M resin and application of this resin for purification of proteins and in some detail the separation of disulfide (SS)- scrambled oligomers of insulin-like growth factor-1 (IGF-1). For this particular application, the intact IGF-1 was used to examine binding and elution conditions of TOYOSCREEN MX-Trp-650M column. Strong binding was obtained at pH 4.0, at which arginine, but not NaCl, resulted in elution. Both NaCl and arginine resulted in elution at pH 6.5. In addition, a pH gradient from 4.0 to 8.5 was effective. When applied to SS-scrambled IGF-1 oligomers, both pH and arginine gradient exhibited an efficient separation of the oligomers.

Quantitative analysis of acid-catalyzed levulinic acid product mixture from cellulose by mixed-mode liquid chromatography

A mixed-mode weak anion-exchange/reversed-phase liquid chromatography (LC) column was successfully applied for the analysis of levulinic acid (4-oxopentanoic acid, LA) product mixture derived from cellulose. Due to the existence of ionic and neutral byproducts, the analysis of the product mixture usually requires ion chromatography, LC and gas chromatography simultaneously. The new method enables accomplishment of the analysis in one LC run within 6min. LC mobile phase of 10mM phosphate buffer containing 5% acetonitrile with pH=5.5 was used. The linear regression coefficients for the UV signal of standard compounds with the corresponding mass concentrations were greater than 0.999. The method recoveries were between 98.57-103.48%. The limits of quantification were 5, 10,1000, 1500 and 3000ng/mL for 5-hydroxymethylfurfural, furfural, acetic acid, formic acid and LA respectively. The mixed-mode column exhibits comprehensive separation mechanism of both reversed-phase and ion-exchange interactions. The mobile phase with different pH, organic modifier solvent and buffer concentration provided flexible LC method for the sample with different complexity.

Synthesis, characterization, and application of a novel multifunctional stationary phase for hydrophilic interaction/reversed phase mixed-mode chromatography

A novel multifunctional stationary phase based on silica gel was synthesised starting from L- isoleucine and 4-phenylbutylamine and evaluated as a hydrophilic interaction/reversed-phase mixed-mode stationary phase for high-performance liquid chromatography (HPLC). The prepared stationary phase was characterized by elemental analysis, infrared spectroscopy (IR), scanning electron microscopy (SEM), Brunauer, Emmett and Teller (BET) and solid-state ¹³C nuclear magnetic resonance (NMR). The mechanisms involved in the chromatographic separation are multi-interaction, including hydrophobic, π-π, hydrogen-bonding, dipole-dipole and ion-dipole interactions. Based on these interactions, successful separation could be achieved among several aromatic compounds having different polarities under both hydrophilic interaction liquid chromatography (HILIC) and reversed phase (RP) condition. Nucleotides/nucleosides were separated in the HILIC mode. The effects of different separation conditions, such as pH value, mobile-phase content, column temperature, buffer concentration and flow rate, on the separation of nucleotides/nucleosides in HILIC mode were investigated. The seven nucleotides/nucleosides were separated within 22min, while six of them were separated within 10min by isocratic elution. To determine the influence of the new multifunctional stationary phase under the RP condition, a number of moderately and weakly polar and nonpolar compounds, such as 10 substituted anilines and eight substituted phenols were separated successfully under the RP condition within 14 and 15min, respectively. Additionally, nine mixtures of polar/nonpolar test compounds were simultaneously separated within 19min, while seven of them were separated within 12min, under HILIC/RP mixed-mode conditions. Chromatographic parameters, such as the retention factor and peak asymmetry factor, were calculated for all of the analytes, while the theoretical plate number was calculated for analytes separated by isocratic elution. Compared to traditional C18 and commercial HILIC columns, the new stationary phase exhibited both HILIC and RPLC performance, and the scope of analyte separation was thus enlarged.

C18-COOH Silica: Preparation, Characterisation and Its Application in Purification of Quaternary Ammonium Alkaloids from Coptis chinensis

INTRODUCTION

Traditional methods for isolating and purifying quaternary ammonium alkaloids from Coptis chinensis do not discriminate the target alkaloids from co-extractives. Mixed-mode analytical chromatography has the potential to improve the separation of analytes in more complex extracts and, when used in a solid-phase extraction mode, improve the purity of isolated compounds.

OBJECTIVE

To examine the high-performance liquid chromatographic separation capabilities of a mixed-mode, silica-based adsorbent and its application to the purification of quaternary ammonium alkaloids from Coptis chinensis based on solid-phase extraction.

METHODOLOGY

The C18-COOH silica was prepared via "thiol-ene" click chemistry. Its chromatographic performance was firstly investigated. It was employed as the solid-phase extraction sorbent to purify quaternary ammonium alkaloids.

RESULTS

Hydrophobic, attractive/repulsive electrostatic and ion-exchange interactions were demonstrated to be the possible retention mechanisms of a C18-COOH silica stationary phase, which could separate analytes of various properties. In addition, to purify quaternary ammonium alkaloids from Coptis chinensis, the solid-phase extraction approach based on the C18-COOH silica provided a slightly higher purification efficiency (6.7%) than an alkaloid-salt precipitation protocol (5.3%). The method had satisfactory reproducibility, re-using the same solid-phase extraction column three times, with relative standard deviations ranging from 1.99% to 8.02% for the six target alkaloids.

CONCLUSION

A multi-functionalised silica was synthesised via "click chemistry". As the high-performance liquid chromatographic stationary phase, the C18-COOH silica could be operated in trimodal reversed-phase/weak cation exchange/hydrophilic interaction mode. The C18-COOH silica also exhibited potential as solid-phase extraction sorbent in the purification of quaternary ammonium alkaloids from complex matrices. Copyright © 2017 John Wiley & Sons, Ltd.

Orthogonal liquid chromatography-mass spectrometry methods for the comprehensive characterization of therapeutic glycoproteins, from released glycans to intact protein level

Proteins are increasingly used as therapeutics. Their characterization is challenging due to their size and inherent heterogeneity notably caused by post-translational modifications, among which glycosylation is probably the most prominent. The glycosylation profile of therapeutic proteins must therefore be thoroughly analyzed. Here, we illustrate how the use of a combination of various cutting-edge LC or LC/MS(/MS) methods, and operating at different levels of analysis allows the comprehensive characterization of both the N- and O-glycosylations of therapeutic proteins without the need for other approaches (capillary electrophoresis, MALDI-TOF). This workflow does not call for the use of highly specialized/custom hardware and software nor an extensive knowledge of glycan analysis. Most notably, we present the point of view of a contract research organization, with the constraints associated to the work in a regulated environment (GxP). Two salient points of this work are i) the use of mixed-mode chromatography as a fast and straightforward mean of profiling N-glycans sialylation as well as an orthogonal method to separate N-glycans co-eluting in the HILIC mode; and ii) the use of widepore HILIC/MS to analyze challenging N/O-glycosylation profiles at both the peptide and subunit levels. A particular attention was given to the sample preparations in terms of duration, specificity, versatility, and robustness, as well as the ease of data processing.

Preparation of a silica stationary phase co-functionalized with Wulff-type phenylboronate and C12 for mixed-mode liquid chromatography

A silica stationary phase was designed and synthesized through the co-functionalization of silica with Wulff-type phenylboronate and C12 for mixed-mode liquid chromatography applications. The as-synthesized stationary phase was characterized by elemental analysis and Fourier Transform-InfraRed Spectroscopy (FT-IR). Retention mechanisms, including boronate affinity (BA), reversed-phase (RP) and anion-exchange (AE), were involved. Retention mechanism switching was easily realized by adjustment of the mobile phase constitution. Cis-diol compounds could be selectively captured under neutral conditions in BA mode and off-line separated in RP mode. Neutral, basic, acidic and amphiprotic compounds were chromatographed on the column in RP chromatography, while inorganic anions were chromatographed in AE chromatography to characterize the mixed-mode nature of the prepared stationary phase. In addition, the RP performance was compared with an octadecyl silica column in terms of column efficiency (N/m), asymmetry factor (A_f), retention factor (k) and resolution (Rs). The prepared stationary phase offered multiple interactions with analytes in addition to hydrophobic interactions under RP elution conditions. Based on the mixed-mode properties, off-line 2D-LC, for selective capture and separation of urinary nucleosides, was successfully realized on a single column, demonstrating its powerful application potential for complex samples.

Hydrophilic interaction and reversed phase mixed-mode liquid chromatography coupled to high resolution tandem mass spectrometry for polar lipids analysis

A hydrophilic interaction liquid chromatography (HILIC) fused-core column (150×2.1mm ID, 2.7μm particle size) and a short reversed-phase liquid chromatography (RPLC) column (20mm×2.1mm ID, 1.9μm) were serially coupled to perform mixed-mode chromatography (MMC) on complex mixtures of phospholipids (PL). Mobile phase composition and gradient elution program were, preliminarily, optimized using a mixture of phosphatidylcholines (PC), phosphatidylethanolamines (PE), their corresponding lyso-forms (LPC and LPE), and sphingomyelins (SM). Thus a mixture of PC extracted from soybean was characterized by MMC coupled to electrospray ionization (ESI) high-resolution Fourier-transform mass spectrometry (FTMS) using an orbital trap analyzer. Several previously undiscovered PC, including positional isomers (i.e. 16:0/19:1 and 19:1/16:0) of PC 35:1 and skeletal isomers (i.e. 18:1/18:2 and 18:0/18:3) of PC 36:3 were identified. Therefore, high-resolution MS/MS spectra unveiled the occurrence of isomers for several overall side chain compositions. The proposed MMC-ESI-FTMS/MS approach revealed an unprecedented capability in disclosing complexity of an actual lipid extract, thus representing a very promising approach to lipidomics.

Purification of bone morphogenetic protein-2 from refolding mixtures using mixed-mode membrane chromatography

In this study, we present the development of a process for the purification of recombinant human bone morphogenetic protein-2 (rhBMP-2) using mixed-mode membrane chromatography. RhBMP-2 was produced as inclusion bodies in Escherichia coli. In vitro refolding using rapid dilution was carried out according to a previously established protocol. Different membrane chromatography phases were analyzed for their ability to purify BMP-2. A membrane phase with salt-tolerant properties resulting from mixed-mode ligand chemistry was able to selectively purify BMP-2 dimer from refolding mixtures. No further purification or polishing steps were necessary and high product purity was obtained. The produced BMP-2 exhibited a biological activity of 7.4 × 10⁵ U/mg, comparable to commercial preparations. Mixed-mode membrane chromatography can be a valuable tool for the direct purification of proteins from solutions with high-conductivity, for example refolding buffers. In addition, in this particular case, it allowed us to circumvent the use of heparin-affinity chromatography, thus allowing the design of an animal-component-free process.

Evaluation and application of a mixed-mode chromatographic stationary phase in two-dimensional liquid chromatography for the separation of traditional Chinese medicine

In this study, two mixed-mode chromatography stationary phases (C8SAX and C8SCX) were evaluated and used to establish a two-dimensional liquid chromatography system for the separation of traditional Chinese medicine. The chromatographic properties of the mixed-mode columns were systematically evaluated by comparing with other three columns of C8, strong anion exchanger, and strong cation exchanger. The result showed that C8SAX and C8SCX had a mixed-mode retention mechanism including electrostatic interaction and hydrophobic interaction. Especially, they were suitable for separating acidic and/or basic compounds and their separation selectivities could be easily adjusted by changing pH value. Then, several off-line 2D-LC systems based on the C8SAX in the first dimension and C8SAX, C8SCX, or C8 columns in the second dimension were developed to analyze a traditional Chinese medicine-Uncaria rhynchophylla. The two-dimensional liquid chromatography system of C8SAX (pH 3.0) × C8SAX (pH 6.0) exhibited the most effective peak distribution. Finally, fractions of U. rhynchophylla prepared from the first dimension were successfully separated on the C8SAX column with a gradient pH. Thus, the mixed-mode stationary phase could provide a platform to separate the traditional Chinese medicine in practical applications.