Fraction transfer process in on-line comprehensive two-dimensional liquid-phase separations

Comprehensive and heart-cutting multidimensional liquid chromatography-mass spectrometry and its applications in food analysis

In food analysis, conventional one-dimensional liquid chromatography methods sometimes lack sufficient separation power due to the complexity and heterogeneity of the analyzed matrices. Therefore, the use of two-dimensional liquid chromatography (2D-LC) turns out to be a powerful tool to consider, especially when coupled to mass spectrometry (MS). This review presents the most remarkable 2D-LC-MS food applications reported in the last 10 years, including a critical discussion of the multiple approaches, modulation strategies as well as the importance of the optimization of the different analytical aspects that will condition the 2D-LC-MS performance. The presence of contaminants in food (food safety), the food quality, and authenticity or the relationship between the beneficial effects of food and human health are some of the fields in which most of the 2D-LC-MS applications are mainly focused. Both heart-cutting and comprehensive applications are described and discussed in this review, highlighting the potential of 2D-LC-MS for the analysis of such complex samples.

Theoretical and practical guidelines for solvent dilution between the two dimensions in online comprehensive two-dimensional liquid chromatography

Online comprehensive two-dimensional liquid chromatography (online LC x LC) has become increasingly popular. Among the different chromatographic modes that can be combined, hydrophilic interaction chromatography (HILIC) and reversed-phase liquid chromatography (RPLC) are particularly interesting because they offer a high degree of orthogonality. However, this combination remains complex due to the incompatibility of the solvents in the two dimensions. To avoid this problem, it is possible to dilute the first dimension (1D) effluent with (zdilution -1) volumes of a weaker solvent added to one volume of 1D-effluent, where zdilution represents the extent to which the fraction volume has been multiplied. This can be done using either active solvent modulation technology or an additional pump, prior to the second dimension analysis. The objective of this study was to develop theoretical models to predict whether or not dilution can be effective, and, if so, what is the minimum zdilution value required. This approach is based on the calculation of the ratio (called xdilution) between the peak standard deviation due to the injection process and the peak standard deviation in the absence of extra-column dispersion. xdilution was calculated from theoretical relationships and plotted as a function of zdilution, to predict the value required to obtain good peak shapes for the compound of interest. The maximum xdilution value was found to be of the order of 1 for chromatographically acceptable peak shapes. The proposed theoretical approach was experimentally validated on a number of representative small molecules and peptides. Agreement between experimental results and theoretical models was very high, especially for small molecules. Finally, it is shown that this approach helps to predict the most appropriate set of conditions in HILIC x RPLC, depending on the compounds to be separated.

Detailed comparison of in-house developed and commercially available heart-cutting and selective comprehensive two-dimensional liquid chromatography systems

Recently, two-dimensional liquid chromatography (2D-LC) has become a popular approach to analyze complex samples. This is partly due to the introduction of commercial 2D-LC systems. In the past, 2D-LC was carried out on in-house developed setups, typically consisting of several switching valves and sample loops as the interface between the two dimensions. Commercial systems usually offer different 2D-LC modes in combination with specialized software to operate the instrument and analyze the data. This makes them highly user-friendly, however, at an increased cost compared to in-house developed setups. This study aims to make a comparison between an in-house developed 2D-LC setup and a commercially available 2D-LC instrument. The comparison is made based on experimental differences, in addition to more general differences, including cost price, flexibility, and ease of operation. Special attention is also paid to the different strategies to deal with the mobile phase incompatibility between the highly orthogonal separation mechanisms considered in this work: hydrophilic interaction liquid chromatography (HILIC) and reversed-phase LC (RPLC). For the commercial 2D-LC instrument, this is done using active solvent modulation (ASM), a valve-based approach allowing the on-line dilution of the effluent eluting from the first dimension column before transfer to the second dimension (2D) column. For the in-house developed setup, a combination of restriction capillaries and a trap column is used. Using a sample of 28 compounds with a large polarity range, peak shapes and recoveries of the 2D-chromatograms are compared for both setups. For early eluting compounds, the selective comprehensive approach, currently only possible on the commercial 2D-LC instrument, results in the best peak shapes and recoveries, however, at the cost of an increased analysis time. In general, depending on the analytical goal (single heart-cut versus full-comprehensive 2D-LC), an in-house developed system can be satisfactory for the analysis of specific target compounds/samples. For more complex problems, it can be interesting to use a more specialized commercial 2D-LC instrument. Overall, this comparison study provides advice for analytical scientists, who are considering to use 2D-LC, on the type of equipment to consider, depending on the needs of their particular applications.

Benchmarking of Two Peptide Clean-Up Protocols: SP2 and Ethyl Acetate Extraction for Sodium Dodecyl Sulfate or Polyethylene Glycol Removal from Plant Samples before LC-MS/MS

The success of bottom-up proteomic analysis frequently depends on the efficient removal of contaminants from protein or peptide samples before LC-MS/MS. For a peptide clean-up workflow, single-pot solid-phase-enhanced peptide sample preparation on carboxylate-modified paramagnetic beads (termed SP2) was evaluated for sodium dodecyl sulfate or polyethylene glycol removal from Arabidopsis thaliana tryptic peptides. The robust and efficient 40-min SP2 protocol, tested for 10-ng, 250-ng, and 10-µg peptide samples, was proposed and benchmarked thoroughly against the ethyl acetate extraction protocol. The SP2 protocol on carboxylated magnetic beads proved to be the most robust approach, even for the simultaneous removal of massive sodium dodecyl sulfate (SDS) and polyethylene glycol (PEG) contaminations from AT peptide samples in respect of the LC-MS/MS data outperforming ethyl acetate extraction.

Reversed HILIC Gradient: A Powerful Strategy for On-Line Comprehensive 2D-LC

The aim of the present work is to evaluate the possibilities and limitations of reversed hydrophilic interaction chromatography (revHILIC) mode in liquid chromatography (LC). This chromatographic mode consists of combining a highly polar stationary phase (bare silica) with a gradient varying from very low (1-5%) to high (40%) acetonitrile content (reversed gradient compared to HILIC). The retention behavior of revHILIC was first compared with that of reversed-phase LC (RPLC) and HILIC using representative mixtures of peptides and pharmaceutical compounds. It appears that the achievable selectivity can be ranked in the order RPLC > revHILIC > HILIC with the two different samples. Next, two-dimensional liquid chromatography (2D-LC) conditions were evaluated by combining RPLC, revHILIC, or HILIC with RPLC in an on-line comprehensive (LC × LC) mode. evHILIC × RPLC not only showed impressive performance in terms of peak capacity and sensitivity, but also provided complementary selectivity compared to RPLC × RPLC and HILIC × RPLC. Indeed, both the elution order and the retention time range differ significantly between the three techniques. In conclusion, there is no doubt that revHILIC should be considered as a viable option for 2D-LC analysis of small molecules and also peptides.

Optimizing transfer and dilution processes when using active solvent modulation in on-line two-dimensional liquid chromatography

Two-dimensional liquid chromatography (2D-LC) is becoming increasingly popular for the analysis of complex samples, which is partly due to the recent introduction of commercial 2D-LC systems. To deal with the mobile phase incompatibility between highly orthogonal retention mechanisms, such as hydrophilic interaction liquid chromatography (HILIC) and reversed-phase LC (RPLC), several strategies have been introduced over the years. One of these strategies is active solvent modulation (ASM), a valve-based approach allowing the on-line dilution of the effluent eluting from the first dimension before transfer to the second dimension. This strategy has gained a lot of attention and holds great potential, however, no clear guidelines are currently in place for its use. Therefore, this study aims to investigate how the ASM process can be optimized when using highly incompatible LC combinations, such as HILIC and RPLC, in a simplified selective comprehensive 2D-LC set-up (sHILIC x RPLC) to suggest guidelines for future users. Using a representative sample, the dilution factor (DF), the duration of the ASM phase, the filling percentage of the sample loops, and their unloading configuration are investigated and optimized. It is observed that a DF of 10 with an optimal ASM phase duration, a sample loop filling of maximum 25%, and an unloading configuration in backflush mode, result in the best peak shapes, intensities, and recoveries for early eluting compounds, while keeping the total analysis time minimal. Based on these results, some general recommendations are made that could also be applied in other 2D-LC modes, such as comprehensive 2D-LC (LC x LC), heart-cutting 2D-LC (LC-LC), and other chromatographic combinations with mobile phase incompatibility issues.

Comprehensive and heart-cutting multidimensional liquid chromatography-mass spectrometry and its applications in food analysis

In food analysis, conventional one-dimensional liquid chromatography methods sometimes lack sufficient separation power due to the complexity and heterogeneity of the analysed matrices. Therefore, the use of two-dimensional liquid chromatography (2D-LC) turns out to be a powerful tool to consider, especially when coupled to mass spectrometry (MS). This review presents the most remarkable 2D-LC-MS food applications reported in the last 10 years, including a critical discussion of the multiple approaches, modulation strategies as well as the importance of the optimisation of the different analytical aspects that will condition the 2D-LC-MS performance. The presence of contaminants in food (food safety), the food quality and authenticity or the relationship between the beneficial effects of food and human health are some of the fields in which most of the 2D-LC-MS applications are mainly focused. Both heart-cutting and comprehensive applications are described and discussed in this review, highlighting the potential of 2D-LC-MS for the analysis of such complex samples.

Segmented two-dimensional liquid chromatography. Proof of concept study

The separation in liquid chromatography is defined either by the space domain where it proceeds until the least retained analyte reaches the outlet of the column or by the time when individual analytes elute out of the column. These two approaches lead to the four possible combinations of two-dimensional liquid chromatography with online space x time coupling being the least experimentally feasible. Here, we show the development of a novel two-dimensional liquid chromatography method combining separation defined by space and the conventional elution-based separation. First-dimension column consisted of four capillary segments coupled serially via two-position six-port valves allowing an online and comprehensive transfer of analytes from the first to the second dimension. After initial experiments using homemade monolithic capillary columns, we tested commercially available columns in both dimensions. We ended with the combination of packed capillary columns in the first dimension and monolithic capillary column in the second dimension. We used a reversed-phase retention mechanism in the first spatial dimension, while HILIC was in the second, time-based dimension. We also developed a theoretical model to describe the proposed two-dimensional separation that was further confirmed by utilizing both an isocratic and gradient elution in the second dimension. Finally, we applied our experimental setup to separate neurotransmitters contained in human urine.

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.

Determination of the polyphenolic content of berry juices using focusing-modulated comprehensive two-dimensional liquid chromatography coupled to mass spectrometry detection

In this work, a comprehensive two-dimensional liquid chromatography system, comprised of a ZIC-HILIC and C18 columns in the first and second dimensions, respectively, was tuned and employed for attaining high resolution profiles of the polyphenolic pattern in seven commercial berry juices. The developed HILIC × RP-LC method was validated in terms of linearity range, correlation coefficients, limit of detection, limit of quantification, precision (intra- and inter-day), and recovery. A total of 104 polyphenolic compounds belonging to different chemical classes (hydroxybenzoic and cinnamic acid derivatives, flavone glycosides, flavonols, flavonol glycosides, dihydroflavonols, and anthocyanin glycosides) have been characterized and quantified in the juices investigated. Despite the constituents being similar, a notable quantitative variation among the analyzed berry species was observed. Elderberry contained the highest amount of polyphenols (918 ± 1.10 mg 100 mL^-1), followed by chokeberry (516 ± 0.08 mg 100 mL^-1). On the other hand, raspberry contained the lowest amount (104 ± 1.21 mg 100 mL^-1). Further, total phenolic, flavonoid, and anthocyanin contents were determined spectrophotometrically, yielding consistent results. The free-radical scavenging activity (DPPH test) and reducing power of the juices, expressed as IC₅₀ (μL mL^-1) and mg ASE mL^-1, varied from 2.79 ± 0.03 (honeyberry) to 31.66 ± 0.02 (blueberry) and from 1.71 ± 0.01 (blueberry) to 8.89 ± 0.12 (chokeberry), respectively. Such a ZIC-HILIC × C18 platform based on focusing modulation, never employed so far for berry juices, showed a remarkable separation capability with high values of corrected peak capacity (up to 1372) and orthogonality (A_o up to 0.80), thus providing a great applicability to be advantageously employed for other complex food samples.

Profiling of sphingolipids in Caenorhabditis elegans by two-dimensional multiple heart-cut liquid chromatography - mass spectrometry

Sphingolipids exert important functions in cells, ranging from stabilising the cell membrane to bioactive signalling in signal transduction pathways. Changed concentrations of sphingolipids are associated with, among others, neurodegenerative and cardiovascular diseases. In this work, we present a novel two-dimensional liquid chromatography method (2D-LC) coupled to tandem mass spectrometry (MS/MS) for the identification of ceramides, hexosylceramides and sphingomyelins in the model organism Caenorhabditis elegans (C. elegans). The method utilises a multiple heart-cut approach with a hydrophilic interaction liquid chromatography (HILIC) separation in the first dimension. The fractions of the sphingolipid classes were cut out and thereby separated from the abundant glycerolipids, which offers a simplified sample preparation and a high degree of automation as it compensates the alkaline depletion step usually conducted prior to the chromatographic analysis. The fractions were stored in a sample loop and transferred onto the second column with the combination of two six port valves. A reversed phase liquid chromatography was performed as the second dimension and allowed for a separation of the species within a sphingolipid class and according to the fatty acid moiety of the sphingolipid. The segregation of the abundant glycerolipids and the reduced matrix effects allowed for better identification of low abundant species, especially dihydro-sphingolipids with a saturated sphingoid base. In addition, the separation of the three fractions was carried out parallel to the separation and equilibration in the first dimension, which leads to no extension of the analysis time for the 2D-LC compared to the one-dimensional HILIC method. In total 45 sphingolipids were detected in the C. elegans lipid extract and identified via accurate mass and MS/MS fragments.

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.

A comprehensive study on the phenomenon of total breakthrough in liquid chromatography

Differences in elution strength between the sample solvent and the mobile phase usually give rise to undesirable effects on the chromatographic separation, which may range from slight broadening to severe peak deformation or even splitting. In the most extreme case, the retention factor of the analyte at the head of the column is so small at the time of injection that part of the analyte goes through the column with very little interaction with the stationary phase and hence elutes very close to the column dead time. This phenomenon is known as breakthrough. Usually, during breakthrough, the retained peak displays a wide array of deformations and it is not rare that multiple retained peaks appear for a given injected analyte. However, under certain conditions, it has been demonstrated that these deleterious effects could fully disappear, leaving only one breakthrough peak and one symmetrical peak on the chromatogram. This so-called "total breakthrough" phenomenon was recently highlighted in the specific context of the 2D-LC separation of peptides but has yet to be explained. In the present paper, we describe the results of a comprehensive study aiming to better understand and define the conditions of emergence of both breakthrough and total breakthrough phenomena in liquid chromatography. The effects of a broad range of parameters, including the nature of the solute, the retention mechanism, the injection and elution conditions, the column temperature, and the injected sample concentration on the occurrence of both phenomena were investigated. While breakthrough was found to occur for all studied compounds, it appears that the presence of positive charges on the molecule is a prerequisite for observing a total breakthrough phenomenon. Among all the parameters investigated in this work, only the injection conditions and the analyte retention were found to be impactful on the onset of both phenomena. This finding allowed us to suggest one necessary and sufficient condition, relying on the injection of critical volumes to observe each respective phenomenon. These critical volumes only depend on the column dead volume and the retention factor of the analyte in the injection solvent.

Reversed phase versus hydrophilic interaction liquid chromatography as first dimension of comprehensive two-dimensional liquid chromatography systems for the elucidation of the polyphenolic content of food and natural products

Comprehensive two-dimensional liquid chromatography is a well-established method for the unraveling of very complex real-world samples. With regard to food and natural products such a technique turned out to be a very promising approach due to its high resolving power and improved identification capability, especially in combination with mass spectrometry. In this context, polyphenols comprise a particular complex class of bioactive compounds, due to their nature and content in commonly consumed foodstuffs, making their analysis challenging. The present contribution shows an overview of the two commonly employed approaches used for polyphenol analysis, viz. RP-LC × RP-LC and HILIC × RP-LC. Furthermore, the latest implementations as well as limitations and future perspectives are critically reported.

Enhancing online protein isolation as intact species from soy flour samples by actively modulated two-dimensional liquid chromatography (2D-LC)

In this study, an enhanced fully automated approach is described for the protein isolation from soy flour samples by two-dimensional liquid chromatography with active modulation interface. The use of two multi-port switching valves is proposed to on-line connect the first to the second dimension column, thus overcoming the problems associated with the re-mixing effects and incompatibility of eluent composition and pH. A 5-cm long C4 analytical column installed in the interface device allows to focus the proteins coming from the first column (size exclusion chromatography), before their selective elution in the second column (reversed-phase). A trap washing step was included in the total workflow, as a desalting step to remove buffer residues from the eluent of the first column and to enhance the chromatographic performances of the second column. The experimental conditions were optimized by analyses of mixed standard solutions of bovine serum albumin, glucose oxidase, immunoglobulin A, thyroglobulin and myoglobin. Then, the optimized 2D-LC method was applied to the protein analysis in extracts of soy flour, known worldwide as one of the major food allergen sources, with the final aim to recovery sufficient protein amounts for the molecular characterization and the assessment of the pattern of allergenic components.

Challenges and Advances in the Fabrication of Monolithic Bioseparation Materials and their Applications in Proteomics Research

High-performance liquid chromatography integrated with tandem mass spectrometry (HPLC-MS/MS) has become a powerful technique for proteomics research. Its performance heavily depends on the separation efficiency of HPLC, which in turn depends on the chromatographic material. As the "heart" of the HPLC system, the chromatographic material is required to achieve excellent column efficiency and fast analysis. Monolithic materials, fabricated as continuous supports with interconnected skeletal structure and flow-through pores, are regarded as an alternative to particle-packed columns. Such materials are featured with easy preparation, fast mass transfer, high porosity, low back pressure, and miniaturization, and are next-generation separation materials for high-throughput proteins and peptides analysis. Herein, the recent progress regarding the fabrication of various monolithic materials is reviewed. Special emphasis is placed on studies of the fabrication of monolithic capillary columns and their applications in separation of biomolecules by capillary liquid chromatography (cLC). The applications of monolithic materials in the digestion, enrichment, and separation of phosphopeptides and glycopeptides from biological samples are also considered. Finally, advances in comprehensive 2D HPLC separations using monolithic columns are also shown.

Selectivity enhancement in capillary electrophoresis by means of two-dimensional separation or dual detection concepts

For the identification and quantification of analytes in complex samples, highly selective analytical strategies are required. The selectivity of single separation techniques such as gas chromatography (GC), liquid chromatography (LC), or capillary electrophoresis (CE) with common detection principles can be enhanced by hyphenating orthogonal separation techniques but also by using complementary detection systems. In this review, two-dimensional systems containing CE in at least one dimension are reviewed, namely LC-CE or 2D CE systems. Particular attention is paid to the aspect of selectivity enhancement due to the orthogonality of the different separation mechanisms. As an alternative concept, dual detection approaches are reviewed using the common detectors of CE such as UV/VIS, laser-induced fluorescence, capacitively coupled contactless conductivity (C⁴D), electrochemical detection, and mass spectrometry. Special emphasis is given to dual detection systems implementing the highly flexible C⁴D as one detection component. Selectivity enhancement can be achieved in case of complementarity of the different detection techniques.

Simultaneous non-polar and polar lipid analysis by on-line combination of HILIC, RP and high resolution MS

Given the chemical diversity of lipids and their biological relevance, suitable methods for lipid profiling and quantification are demanded to reduce sample complexity and analysis times. In this work, we present a novel on-line chromatographic method coupling hydrophilic interaction liquid chromatography (HILIC) dedicated to class-specific separation of polar lipid to reversed-phase chromatography (RP) for non-polar lipid analysis. More specifically, the void volume of the HILIC separation-consisting of non-polar lipids- is transferred to the orthogonal RP column enabling the on-line combination of HILIC with RP without any dilution in the second dimension. In this setup the orthogonal HILIC and RP separations were performed in parallel and the effluents of both columns were combined prior to high-resolution MS detection, offering the full separation space in one analytical run. Rapid separation for both polar and non-polar lipids within only 15 min (including reequilibration time) was enabled using sub-2 μm particles and UHPLC. The method proved to be robust with excellent retention time stability (RSDs < 1%) and LODs in the fmol to pmol (absolute on column) range even in the presence of complex biological matrix such as human plasma. The presented high-resolution LC-MS/MS method leads to class-specific separation of polar lipids and separation of non-polar lipids which is lost in conventional HILIC separations. HILIC-RP-MS is a promising tool for targeted and untargeted lipidomics workflows as three interesting features are combined namely (1) the decreased run time of state of the art shotgun MS methods, (2) the elevated linear dynamic range inherent to chromatographic separation and (3) increased level of identification by separation of polar and non-polar lipid classes.

Comprehensive on-line two-dimensional liquid chromatography × supercritical fluid chromatography with trapping column-assisted modulation for depolymerised lignin analysis

Lignin depolymerisation produces a large variety of low molecular weight phenolic compounds that can be upgraded to value-added chemicals. Detailed analysis of these complex depolymerisation mixtures is, however, hampered by the lack of resolving power of traditional analysis techniques. In this study, a novel online comprehensive two-dimensional reversed-phase liquid chromatography (RPLC) × supercritical fluid chromatography (SFC) method with trapping column interface was developed for the separation of phenolic compounds in depolymerised lignin samples. The trapping capacities of different trapping columns were evaluated. The influence of large volume water-containing injection on SFC performance was studied. The relation between peak capacity and first dimension flow rate and gradient was investigated. The optimized method was applied for the analysis of a depolymerised lignin sample. The RPLC × SFC system exhibited high degree of orthogonality. Compared with traditional loop based interface, trapping column interface can significantly shorten the analysis time and offer higher detectability, with the disadvantage of more severe undersampling in the first dimension.

Optimizing separations in online comprehensive two-dimensional liquid chromatography

Online comprehensive two-dimensional liquid chromatography has become an attractive option for the analysis of complex nonvolatile samples found in various fields (e.g. environmental studies, food, life, and polymer sciences). Two-dimensional liquid chromatography complements the highly popular hyphenated systems that combine liquid chromatography with mass spectrometry. Two-dimensional liquid chromatography is also applied to the analysis of samples that are not compatible with mass spectrometry (e.g. high-molecular-weight polymers), providing important information on the distribution of the sample components along chemical dimensions (molecular weight, charge, lipophilicity, stereochemistry, etc.). Also, in comparison with conventional one-dimensional liquid chromatography, two-dimensional liquid chromatography provides a greater separation power (peak capacity). Because of the additional selectivity and higher peak capacity, the combination of two-dimensional liquid chromatography with mass spectrometry allows for simpler mixtures of compounds to be introduced in the ion source at any given time, improving quantitative analysis by reducing matrix effects. In this review, we summarize the rationale and principles of two-dimensional liquid chromatography experiments, describe advantages and disadvantages of combining different selectivities and discuss strategies to improve the quality of two-dimensional liquid chromatography separations.

Recent developments in capillary and microchip electroseparations of peptides (2015-mid 2017)

The review brings a comprehensive overview of recent developments and applications of high performance capillary and microchip electroseparation methods (zone electrophoresis, isotachophoresis, isoelectric focusing, affinity electrophoresis, electrokinetic chromatography, and electrochromatography) to analysis, microscale isolation, purification, and physicochemical and biochemical characterization of peptides in the years 2015, 2016, and ca. up to the middle of 2017. Advances in the investigation of electromigration properties of peptides and in the methodology of their analysis (sample preseparation, preconcentration and derivatization, adsorption suppression and EOF control, and detection) are described. New developments in particular CE and CEC methods are presented and several types of their applications to peptide analysis are reported: qualitative and quantitative analysis, determination in complex (bio)matrices, monitoring of chemical and enzymatical reactions and physical changes, amino acid, sequence and chiral analysis, and peptide mapping of proteins. Some micropreparative peptide separations are shown and capabilities of CE and CEC methods to provide important physicochemical characteristics of peptides are demonstrated.