Comprehensive analysis of pharmaceutical products using simultaneous mixed-mode (ion-exchange/reversed-phase) and hydrophilic interaction liquid chromatography

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.

A simple method for the determination of glyphosate, glufosinate and their metabolites in biological specimen by liquid chromatography/tandem mass spectrometry: an application for forensic toxicology

Glyphosate (GLYP) and glufosinate (GLUF) are phosphorus-containing amino acid type herbicides that are used worldwide. With their rising consumptions, fatal intoxication cases due to these herbicides, whether accidental or intentional, cannot be ignored. Both compounds are difficult to detect, and their pretreatment for instrumental analysis are complicated and time-consuming. Our aim was to develop a simple and rapid quantification method for the two herbicides and their metabolites with liquid chromatography/tandem mass spectrometry (LC/MS/MS). We also compared 2-amino-4-phosphonobutyric acid and DL-2-amino-5-phosphonopentanoic acid as alternative internal standards (IS) to GLYP13C2 15N. Herbicide-containing specimens were highly diluted, evaporated to dryness, and derivatized with acetate/acetic anhydride and trimethyl orthoacetate for 30 min. at 120°C. Our optimized LC conditions successfully separated the target analytes, with acceptable linearities (R 2>0.98) and matrix effects (65%-140%). Accuracy and precision ranged from 80.2 % to 111 %, and from 1.3 % to 13 % at the higher concentration, respectively.The concentration of the herbicides and their metabolites were investigated in a postmortem case of suspected herbicide poisoning cases, in which we detected GLYP and its metabolites. Using one of the three ISs, the GLYP concentrations ranged from 3.1 to 3.5 mg/mL, and 3.3 to 4.5 mg/mL in plasma and urine, respectively; GLYP metabolite concentrations in plasma and urine were 18 to 20 μg/mL and 44 to 54 μg/mL. We thus succeeded in developing a rapid method without extraction for measuring GLYP and GLUF along with their metabolites, and demonstrated its practical applicability.

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.

MOF-74@SiO2 core-shell stationary phase: Preparation and its applications for mixed-mode chromatographic separation

The development of versatile mixed-mode stationary phase materials is of important meanings for solving the increasing demands for real sample analysis. Herein, with 2,5-dihydroxyterephthalic acid as the organic ligand and nickel as the metal centre, MOF-74 nanocrystal materials were facilely grafted on the surface of carboxyl-functionalized silica gel via layer-by-layer assembling technique. The structures of the monodisperse MOF-74@SiO₂ material were proved by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, elemental analysis, thermogravimetric analysis, and Brunauer-Emmett-Teller specific surface area and pore size analyzer, respectively. Because the introduced 2,5-dihydroxyterephthalic acid is of hydrophilic carboxyl and hydroxyl groups, the packed MOF-74@SiO₂ column reveals hydrophilic interaction/reversed-phase mixed-mode retention properties. Compared with commercial C₈ column or silica-based column, the MOF-74@SiO₂ column shows distrinct separation selectivity in short separation time for polycyclic aromatic hydrocarbons, phenolic compounds and polar sulfonamide compounds. The developed MOF-74@SiO₂ column was further successfully applied for the separation and detection of illegal addition of glucocorticoid in children's face cream as well as sulfonamides veterinary drug residues in pure milk. The research provides a simple and convenient approach to prepare multifunctional MOFs-based stationary phase materials.

Trends in sample preparation and separation methods for the analysis of very polar and ionic compounds in environmental water and biota samples

Recent years showed a boost in knowledge about the presence and fate of micropollutants in the environment. Instrumental and methodological developments mainly in liquid chromatography coupled to mass spectrometry hold a large share in this success story. These techniques soon complemented gas chromatography and enabled the analysis of more polar compounds including pesticides but also household chemicals, food additives, and pharmaceuticals often present as traces in surface waters. In parallel, sample preparation techniques evolved to extract and enrich these compounds from biota and water samples. This review article looks at very polar and ionic compounds using the criterion log P ≤ 1. Considering about 240 compounds, we show that (simulated) log D values are often even lower than the corresponding log P values due to ionization of the compounds at our reference pH of 7.4. High polarity and charge are still challenging characteristics in the analysis of micropollutants and these compounds are hardly covered in current monitoring strategies of water samples. The situation is even more challenging in biota analysis given the large number of matrix constituents with similar properties. Currently, a large number of sample preparation and separation approaches are developed to meet the challenges of the analysis of very polar and ionic compounds. In addition to reviewing them, we discuss some trends: for sample preparation, preconcentration and purification efforts by SPE will continue, possibly using upcoming mixed-mode stationary phases and mixed beds in order to increase comprehensiveness in monitoring applications. For biota analysis, miniaturization and parallelization are aspects of future research. For ionic or ionizable compounds, we see electromembrane extraction as a method of choice with a high potential to increase throughput by automation. For separation, predominantly coupled to mass spectrometry, hydrophilic interaction liquid chromatography applications will increase as the polarity range ideally complements reversed phase liquid chromatography, and instrumentation and expertise are available in most laboratories. Two-dimensional applications have not yet reached maturity in liquid-phase separations to be applied in higher throughput. Possibly, the development and commercial availability of mixed-mode stationary phases make 2D applications obsolete in semi-targeted applications. An interesting alternative will enter routine analysis soon: supercritical fluid chromatography demonstrated an impressive analyte coverage but also the possibility to tailor selectivity for targeted approaches. For ionic and ionizable micropollutants, ion chromatography and capillary electrophoresis are amenable but may be used only for specialized applications such as the analysis of halogenated acids when aspects like desalting and preconcentration are solved and the key advantages are fully elaborated by further research. Graphical abstract.

A new strategy for the preparation of mixed-mode chromatographic stationary phases based on modified dialdehyde cellulose

A new strategy for the preparation of mixed-mode chromatographic stationary phases based on modified dialdehyde cellulose was proposed. Two novel mixed-mode chromatographic stationary phases, dicarboxyl cellulose-modified silica (DCC/SiO₂) and (S)-α-phenylethylamine-bonded DCC/SiO₂ ((S)-α-PEA/DCC/SiO₂), were prepared by utilizing the easy functionalization characteristics of dialdehyde cellulose. The chromatographic evaluation showed that DCC/SiO₂ column could be used in hydrophilic interaction liquid chromatography (HILIC) and ion exchange chromatography (IEC) modes, (S)-α-PEA/DCC/SiO₂ column could be used in HILIC, IEC and chiral separation modes. The DCC/SiO₂ column and (S)-α-PEA/DCC/SiO₂ column exhibited excellent chromatographic performance by separating strongly polar compounds, phenylamines and chiral compounds in the above separation modes. The preparation method of modified dialdehyde cellulose-based mixed-mode chromatographic stationary phases was simple, and also provided a new idea for the development of the subsequent novel mixed-mode chromatographic stationary phases.

Profiling cocaine residues and pyrolytic products in wastewater by mixed-mode liquid chromatography-tandem mass spectrometry

This work provides a new analytical method for the determination of cocaine, its metabolites benzoylecgonine and cocaethylene, the pyrolytic products anhydroecgonine and anhydroecgonine methyl ester, and the pharmaceutical levamisole in wastewater. Samples were solid-phase extracted and extracts analyzed by liquid chromatography-tandem mass spectrometry using, for the first time in the illicit drug field, a stationary phase that combines reversed-phase and weak cation-exchange functionalities. The overall method performance was satisfactory, with limits of detection below 1 ng/L, relative standard deviations below 21%, and percentages of recovery between 93% and 121%. Analysis of 24-hour composite raw wastewater samples collected in Santiago de Compostela (Spain) and Brasilia (Brazil) highlighted benzoylecgonine as the compound showing the highest population-normalized mass loads (300-1000 mg/day/1000 inhabitants). In Brasilia, cocaine and levamisole loads underwent an upsurge on Sunday, indicating a high consumption, and likely a direct disposal, of cocaine powder on this day. Conversely, the pyrolytic product resulting from the smoke of crack, anhydroecgonine methyl ester, and its metabolite anhydroecgonine were relatively stable over the four days, agreeing with a non-recreational-associated use of crack.

Core-Shell Metal-Organic Frameworks as the Mixed-Mode Stationary Phase for Hydrophilic Interaction/Reversed-Phase Chromatography

Stationary phases with mixed-mode mechanisms have emerged as a hot research topic. In the present research, monodisperse core-shell UiO-67@SiO₂ materials were prepared and further served as the packed column for mixed-mode hydrophilic interaction liquid chromatography/reversed-phase liquid chromatography. The developed UiO-67@SiO₂ materials were characterized via thermogravimetric analysis, scanning electron microscopy, X-ray Powder diffraction, and Fourier transform infrared techniques. The developed UiO-67@SiO₂ column shows flexible selectivity for separation of both hydrophobic (anilines, alkylbenzenes, and polycyclic aromatic hydrocarbons) and hydrophilic (thioureas) compounds. Furthermore, the UiO-67@SiO₂ column was also utilized to characterize potential pollutants in lake water samples. In summary, the UiO-67@SiO₂ column provided flexible selectivity and wide-range retention behaviors for both hydrophilic and hydrophobic analytes.

Monolith columns for liquid chromatographic separations of intact proteins: A review of recent advances and applications

In this article we survey 256 references (with an emphasis on the papers published in the past decade) on monolithic columns for intact protein separation. Protein enrichment and purification are included in the broadly defined separation. After a brief introduction, we describe the types of monolithic columns and modes of chromatographic separations employed for protein separations. While the majority of the work is still in the research and development phase, papers have been published toward utilizing monolithic columns for practical applications. We survey these papers as well in this review. Characteristics of selected methods along with their pros and cons will also be discussed.

Screening for Polar Chemicals in Water by Trifunctional Mixed-Mode Liquid Chromatography-High Resolution Mass Spectrometry

The presence of persistent and mobile organic contaminants (PMOC) in aquatic environments is a matter of high concern due to their capability of crossing through natural and anthropogenic barriers, even reaching drinking water. Most analytical methods rely on reversed-phase liquid chromatography (RPLC), which is quite limited for the detection of very polar chemicals. Thus, many of these PMOCs may have not been recognized as water pollutants yet, due to the lack of analytical methods capable to detect them. Mixed-mode LC (MMLC), providing the combination of RP and ion-exchange functionalities is explored in this work with a trifunctional column, combining RPLC, anion and cation exchange, which allows the simultaneous determination of analytes with extremely different properties. A nondiscriminant sample concentration step followed by a MMLC-high resolution mass spectrometry method was developed for a group of 37 very polar model chemicals with different acid/base functionalities. The overall method performance was satisfactory with a mean limit of detection of 50 ng/L, relative standard deviation lower than 20% and overall recoveries (including matrix effects) higher than 60% for 54% of model compounds. Then, the method was applied to 15 real water samples, by a suspect screening approach. For those detected PMOC with standard available, a preliminary estimation of concentrations was also performed. Thus, 22 compounds were unequivocally identified in a range of expected concentrations from 6 ng/L to 540 μg/L. Some of them are well-known PMOC, such as acesulfame, perfluorobutanoic acid or metformin, but other novel pollutants were also identified, as for example di-o-tolylguanidine or trifluoromethanesulfonic acid, which had not or were scarcely studied in water so far.

Mixed-mode chromatography in pharmaceutical and biopharmaceutical applications

Mixed-mode chromatography (MMC) is a fast growing area in recent years, thanks to the new generation of mixed-mode stationary phases and better understanding of multimode interactions. MMC has superior applications in the separation of compounds that are not retained or not well resolved by typical reversed-phase LC methods, especially for polar and charged molecules. Due to the multiple retention modes that a single MMC column can offer, often MMC provides additional dimension to a separation method by adjusting the mobile phase conditions. Mixed-mode media is also an effective way to clean up complex sample matrices for purification purposes or for sensitive detection of trace amounts of analytes. In this article, we discuss mixed-mode stationary phases and separation mechanisms and review recent advances in pharmaceutical and biopharmaceutical applications including the analysis and/or purification of counterions, small molecule drugs, impurities, formulation excipients, peptides and proteins.

Imidazolium embedded C8 based stationary phase for simultaneous reversed-phase/hydrophilic interaction mixed-mode chromatography

A new imidazolium embedded C8 based stationary phase (SIL-MPS-VOL) was facilely prepared by two steps and characterized by Fourier transform infrared spectrometry and thermogravimetric analysis. Due to the introduction of quaternary imidazolium group to the traditional C8 stationary phase, the developed SIL-MPS-VOL column demonstrated both reversed-phase liquid chromatography (RPLC) and hydrophilic interaction liquid chromatography (HILIC) retention mechanisms. A series of hydrophobic and hydrophilic test samples, including benzene homologues, anilines, positional isomers, nucleosides and nucleotides, were used to evaluate the developed SIL-MPS-VOL stationary phase. A rapid separation time, high separation efficiency and planar selectivity were achieved, compared with the commercially available C8 column. Moreover, the developed stationary phase was further used to detect and separate of melamine in powdered infant formula and high polar component of secondary metabolites of Trichoderma, and improved separation efficiency was achieved, indicating the potential merits of the developed SIL-MPS-VOL stationary phase for simultaneous separation of complex hydrophobic and hydrophilic samples with high selectivity.