New zwitterionic polymethacrylate monolithic columns for one- and two-dimensional microliquid chromatography

Liquid chromatography at the university of pardubice: a tribute to Professor Pavel Jandera

Pavel Jandera was a world-leading analytical chemist who devoted his entire professional life to research in the field of high-performance liquid chromatography. During all his scientific career, he worked at the Department of Analytical Chemistry at the University of Pardubice, Czech Republic. His greatest contribution to the field of liquid chromatography was the introduction of a comprehensive theory of liquid chromatography with programmed elution conditions. He was also involved in the research of gradient elution techniques in preparative chromatography, modeling of retention and selectivity in various phase systems, preparation of organic monolithic microcolumns and, last but not least, in the development of theory and practical applications of two-dimensional liquid chromatography, mainly in the comprehensive form. In this review article, we have tried to capture the highlights of his scientific career and provide the readers with a detailed overview of Pavel Jandera's contribution to the evolution of separation sciences. This article is protected by copyright. All rights reserved.

Strategies to circumvent the solvent strength mismatch problem in online comprehensive two-dimensional liquid chromatography

On-line comprehensive two-dimensional liquid chromatography is a powerful technique for the separation of highly complex samples. Due to the addition of the second dimension of separation, impressive peak capacities can be obtained within a reasonable analysis time compared to one-dimensional liquid chromatography. In online comprehensive two-dimensional liquid chromatography, the separation power is maximized by selecting two separation dimensions as orthogonal as possible, which most often requires the combination of different mobile phases and stationary phases. The online transfer of a given solvent from the first dimension to the second dimension may cause severe injection effects in the second dimension, mostly due to solvent strength mismatch. Those injection effects may include peak broadening, peak distortion, peak splitting or breakthrough phenomenon. They are often found to reduce significantly the peak capacity and the peak intensity. To overcome such effects, arising specifically in online comprehensive two-dimensional liquid chromatography, different methods have been developed over the years. In this review, we focused on the most recently reported ones. A critical discussion, supported by a theoretical approach, gives an overview of their advantages and drawbacks.

Recent applications of retention modelling in liquid chromatography

Recent applications of retention modelling in liquid chromatography (2015–2020) are comprehensively reviewed. The fundamentals of the field, which date back much longer, are summarized. Retention modeling is used in retention‐mechanism studies, for determining physical parameters, such as lipophilicity, and for various more‐practical purposes, including method development and optimization, method transfer, and stationary‐phase characterization and comparison. The review focusses on the effects of mobile‐phase composition on retention, but other variables and novel models to describe their effects are also considered. The five most‐common models are addressed in detail, i.e. the log‐linear (linear‐solvent‐strength) model, the quadratic model, the log–log (adsorption) model, the mixed‐mode model, and the Neue–Kuss model. Isocratic and gradient‐elution methods are considered for determining model parameters and the evaluation and validation of fitted models is discussed. Strategies in which retention models are applied for developing and optimizing one‐ and two‐dimensional liquid chromatographic separations are discussed. The review culminates in some overall conclusions and several concrete recommendations.

Hydrophilic Interaction Chromatography Analysis of Esculin in Ointments with UV Detection

Background:

Esculin (ESCN) is used in the pharmaceutical industry with intravenous effect, stimulant and anti-inflammatory capillaries, like vitamin P. It is a significant component of many anti-inflammatory remedies such as esqusan, esflazid and anavenol [14]. It is also found in numerous other remedies available in the market such as proctosone, anustat, and ariproct.

Objective:

To determine experimental conditions, to elucidate retention behavior of esculin in HILIC mode. Moreover, to suggest new ways to separate and determinate esculin in ointments.

Methods:

Two hydrophilic columns were obtained by attaching molecules of sulfobetaine to polystyrene- divinylbenzene particles were studied for chromatographic separation of esculin. The various lengths of the chain are used as an investigative instrument for esculin retention conduct. The change of ACN percentage, buffer concentrations and pH of mobile phase in order to study the retention conduct of esculin.

Results:

A mixed mode hydrophilic interaction and ion exchange is the separation mechanism of esculin. A calibration graph was created for two columns. The concentration range was 8-1200 ng.ml-1, LOD 2.33 and 1.40, RSD% 0.31-1.02, , LOQ 7.07 and 4.25 ng.ml-1, Erel% 0.83 ± 0.68 and 0.545 ± 0.45, Recovery% 100.86 ± 0.68 and 1054 ± 0.45.

Conclusion:

The findings of the current study introduced new ZIC-HILIC methods for the separation and quantitation of esculin.

Superhydrophilicity and strong salt-affinity: Zwitterionic polymer grafted surfaces with significant potentials particularly in biological systems

In recent years, zwitterionic polymers have been frequently reported to modify various surfaces to enhance hydrophilicity, antifouling and antibacterial properties, which show significant potentials particularly in biological systems. This review focuses on the fabrication, properties and various applications of zwitterionic polymer grafted surfaces. The "graft-from" and "graft-to" strategies, surface grafting copolymerization and post zwitterionization methods were adopted to graft lots type of the zwitterionic polymers on different inorganic/organic surfaces. The inherent hydrophilicity and salt affinity of the zwitterionic polymers endow the modified surfaces with antifouling, antibacterial and lubricating properties, thus the obtained zwitterionic surfaces show potential applications in biosystems. The zwitterionic polymer grafted membranes or stationary phases can effectively separate plasma, water/oil, ions, biomolecules and polar substrates. The nanomedicines with zwitterionic polymer shells have "stealth" effect in the delivery of encapsulated drugs, siRNA or therapeutic proteins. Moreover, the zwitterionic surfaces can be utilized as wound dressing, self-healing or oil extraction materials. The zwitterionic surfaces are expected as excellent support materials for biosensors, they are facing the severe challenges in the surface protection of marine facilities, and the dense ion pair layers may take unexpected role in shielding the grafted surfaces from strong electromagnetic field.

One-pot preparation of zwitterionic sulfoalkylbetaine monolith for rapid and efficient separation of lysozyme from egg white

A porous zwitterionic monolithic column was prepared to rapidly and efficiently separate lysozyme from egg white. The monolith was synthesized in a stainless steel HPLC column (5 cm × 4.6 mm i.d.) by in-situ thermal initiated co-polymerization of N,N-dimethyl-N-methacryloxyethyl-N-(3-sulfopropyl) ammonium betaine (MSA) and ethylene dimethacrylate (EDMA). Due to the combination of quaternary ammonium and sulfonic groups on the monolithic matrix in one-pot process, the hydrophobic carbon chain and hydrophilic radical were obtained, which provided multiple driving forces for neutral, basic and acidic analytes, thus mix-mode chromatography mechanism contributed to the retention of different charged proteins. Properties such as composition, morphology and stability of the MSA-co-EDMA monolithic column were characterized by various analytical methods and the results showed that the monolith has large through-pores, good hydrophilicity and permeability. The effects of mobile phase pH and ionic strength on proteins were investigated, drawing the conclusion that the main adsorption and elution mechanism of lysozyme on MSA-co-EDMA monolith was electrostatic interaction, while those of other proteins included hydrophobic, hydrophilic and electrostatic interactions. Therefore, efficient separation of lysozyme and other proteins could be successfully achieved by switching the pH of mobile phase. Lysozyme can be adsorbed using 20 mmol/L phosphate buffer (pH 7.0) and eluted with 20 mmol/L phosphate buffer (pH 2.0). To prove the practicality of the monolithic column, it was also applied in the separation of lysozyme in egg white, which means the work has the potential for further development in proteome analysis of real biological samples.

Multichannel separation device with parallel electrochemical detection

A device with four parallel channels was designed and manufactured by 3D printing in titanium. A simple experimental setup allowed splitting of the mobile phase in four parallel streams, such that a single sample could be analysed four times simultaneously. The four capillary channels were filled with a monolithic stationary phase, prepared using a zwitterionic functional monomer in combination with various dimethacrylate cross-linkers. The resulting stationary phases were applicable in both reversed-phase and hydrophilic-interaction retention mechanisms. The mobile-phase composition was optimized by means of a window diagram so as to obtain the highest possible resolution of dopamine precursors and metabolites on all columns. Miniaturized electrochemical detectors with carbon fibres as working electrodes and silver micro-wires as reference electrodes were integrated in the device at the end of each column. Experimental separations were successfully compared with those predicted by a three-parameter retention model. Finally, dopamine was determined in human urine to further confirm applicability of the developed device.

Controlling selectivity of polymer-based monolithic stationary phases

In this work, we aimed to prepare a monolithic capillary column that allowed an isocratic separation of ten dopamine precursors and metabolites in a single run. Segments of five zwitterion sulfobetaine polymer monoliths have been modified by zwitterion phoshorylcholine by using an ultraviolet-initiated two-step photografting. Columns with 0, 33, 50, 66, and 100% of modified length were prepared. Effect of length of the modified segment and mobile phase composition has been tested. All columns provided dual-retention mechanism with reversed-phase retention in highly aqueous mobile phase and hydrophilic interaction mechanism in highly organic mobile phase. The retention mechanism was controlled by the composition of the mobile phase and has been described by a three-parameter model. We have used regression parameters to characterize the retention of analyzed compounds and to study individual pathways of dopamine metabolism. Comprehensive optimization of mobile phase composition allowed to find an optimal composition of the mobile phase and stationary phase surface chemistry arrangement to achieve desired separation. Optimized columns provided an isocratic separation of all tested compounds in less than nine min.

Mobile phase effects in reversed-phase and hydrophilic interaction liquid chromatography revisited

Correct adjustment of the mobile phase is equally important as the selection of the appropriate column for the separation of polar compounds in LC. Both solvophobic and selective polar interactions control the retention in the Reversed Phase and Hydrophilic Interaction modes. The retention models describing the effects of the volume fraction of the strong eluent component in binary mobile phases on the sample retention factors apply in a limited mobile phase composition range. We introduced a three-parameter retention model, which provides improved prediction of retention over a broad mobile phase range, under isocratic and gradient elution conditions. The model does not imply any assumptions concerning either adsorption or partition distribution mechanism, but allows estimating retention in pure strong and in pure weak mobile phase components. The experimental retention data for phenolic acids and flavones on several core-shell columns with different types of stationary phases agree with the theory. Many polar columns with important structural hydrophobic moieties show dual retention mechanism, (Reversed Phase in water rich mobile phases and Hydrophilic Interaction at high acetonitrile concentrations). It is possible to select the mobile phase compositions in each of the two modes for separations of samples containing compounds largely differing in polarity. The three-parameter model describes the retention in each mode, with separately determined best-fit parameters. We applied the two-mode model to the retention data of sulfonamides and benzoic acid related compounds on a new polymethacrylate zwitterionic monolithic micro-column.

Recent advances in nonpolar and polar organic monoliths for HPLC and CEC

This article is aimed at providing a review of the progress made in the field over the period 2011 to present in order to expand in parts on two previous reviews (S. Karenga and Z. El Rassi, Electrophoresis, 2011, 32, 90-104; D. Gunasena and Z. El Rassi, Electrophoresis, 2012, 33, 251-261). In brief, this review article describes progress made in nonpolar and polar monoliths used in RP HPLC and CEC and in hydrophilic interaction LC/CEC, respectively. This article is by no means an exhaustive review of the literature; it is rather a survey of the recent progress made in the field with 69 references published on nonpolar and polar polymeric monoliths.

Separation of nucleobases, nucleosides, and nucleotides using two zwitterionic silica-based monolithic capillary columns coupled with tandem mass spectrometry

The capability of employing synthesized zwitterionic silica-based monolithic capillary columns (140 mm × 0.1mm) for separation of highly polar and hydrophilic nucleobases, nucleosides, and nucleotides in hydrophilic interaction chromatography is reported. The suitability of the columns for on-line conjunction with electrospray tandem mass spectrometry was explored. Our results show that the grafted layer of zwitterionic monomer ([2-(methacryloyloxy)ethyl]-dimethyl-(3-sulfopropyl)-ammonium hydroxide or 2-methacryloyloxyethyl phosphorylcholine) on the silica monolithic surface significantly improved the separation selectivity and reproducibility, as compared to the bare silica monolith. The stepwise elution from 90% to 70% of acetonitrile enabled separation of a complex sample mixture containing 21 compounds with a total analysis time less than 40 min.