A microfluidic chip-based capillary zone electrophoresis-mass spectrometry method for measuring adenosine 5'-Triphosphate and its similar nucleotide analogues

BACKGROUND

Extracellular ATP is involved in disorders that cause inflammation of the airways and cough, thus limiting its release has therapeutic benefits. Standard luminescence-based ATP assays measure levels indirectly through enzyme degradation and do not provide a simultaneous readout for other nucleotide analogues. Conversely, mass spectrometry can provide direct ATP measurements, however, common RPLC and HILIC methods face issues because these molecules are unstable, metal-sensitive analytes which are often poorly retained. These difficulties have traditionally been overcome using passivation or ion-pairing chromatography, but these approaches can be problematic for LC systems. As a result, more effective analytical methods are needed.

RESULTS

Here, we introduce a new application that uses microfluidic chip-based capillary zone electrophoresis-mass spectrometry (μCZE-MS) to measure ATP and its analogues simultaneously in biofluids. The commercially available ZipChip Interface and a High-Resolution Bare-glass microchip (ZipChip, HRB, 908 Devices Inc.) coupled to a Thermo Scientific Tribrid Orbitrap, were successfully used to separate and detect various nucleotide standards, as well as ATP, ADP, AMP, and adenosine in plasma and BALF obtained from naïve Brown Norway rats. The findings demonstrate that this approach can rapidly and directly detect ATP and its related nucleotide analogues, while also highlighting the need to preserve these molecules in biofluids with chelators like EDTA. In addition, we demonstrate that this μCZE-MS method is also suitable for detecting a variety of metabolites, revealing additional potential future applications.

SIGNIFICANCE

This innovative μCZE-MS approach provides a robust new tool to directly measure ATP and other nucleotide analogues in biofluids. This can enable the study of eATP in human disease and potentially contribute to the creation of ATP-targeting therapies for airway illnesses.

Ion mobility in gas and liquid phases: How much orthogonality is obtained in capillary electrophoresis-ion mobility-mass spectrometry?

Ion mobility-mass spectrometry (IM-MS) is an ever-evolving tool to separate ions in the gas phase according to electrophoretic mobility with subsequent mass determination. CE is rarely coupled to IM-MS, possibly due to similar separation mechanisms based on electrophoretic mobility. Here, we investigate the orthogonality of CE and ion mobility (IM) by analyzing a complex peptide mixture (tryptic digest of HeLa proteins) with trapped ion mobility mass spectrometry (TIMS-MS). Using the nanoCEasy interface, excellent sensitivity was achieved by identifying thousands of peptides and achieving a peak capacity of 7500 (CE: 203-323 in a 150 cm long capillary, IM: 27-31). Plotting CE versus mass and CE versus (inverse) mobility, a clear grouping in curved striped patterns is observed according to the charge-to-size and mass-to-charge ratios. The peptide charge in the acidic background electrolyte can be estimated from the number of basic amino acids, with a few exceptions where neighboring effects reduce the positive charge. A surprisingly high orthogonality of CE and IM is observed, which is obviously caused by solvation effects leading to different charges and sizes in the liquid phase compared to the gas phase. A high orthogonality of CE and ion mobility is expected to be observed for other peptide samples as well as other substance classes, making CE-IM-MS a promising tool for various applications.

Investigating the Merits of Microfluidic Capillary Zone Electrophoresis-Mass Spectrometry (CZE-MS) in the Bottom-Up Characterization of Larger RNAs

Established bottom-up approaches for the characterization of nucleic acids (NAs) rely on the strand-cleavage activity of nucleotide-specific endonucleases to generate smaller oligonucleotides amenable to gas-phase sequencing. The complexity of these hydrolytic mixtures calls for the utilization of a front-end separation to facilitate full mass spectrometric (MS) characterization. This report explored the merits of microfluidic capillary zone electrophoresis (CZE) as a possible alternative to common liquid chromatography techniques. An oligonucleotide ladder was initially employed to investigate the roles of fundamental analyte features and experimental parameters in determining the outcome of CZE-MS analyses. The results demonstrated the ability to fully resolve the various rungs into discrete electrophoretic peaks with full-width half-height (FWHH) resolution that was visibly affected by the overall amount of material injected into the system. Analogous results were obtained from a digestion mixture prepared by treating yeast tRNAPhe (75 nt) with RNase T1, which provided several well-resolved peaks in spite of the increasing sample heterogeneity. The regular shapes of such peaks, however, belied the fact that most of them contained sets of comigrating species, as shown by the corresponding MS spectra. Even though it was not possible to segregate each species into an individual electrophoretic peak, the analysis still proved capable of unambiguously identifying a total of 29 hydrolytic products, which were sufficient to cover 96% of the tRNAPhe's sequence. Their masses accurately reflected the presence of modified nucleotides characteristic of this type of substrate. The analysis of a digestion mixture obtained from the 364 nt HIV-1 5'-UTR proved to be more challenging. The electropherogram displayed fewer well-resolved peaks and significantly greater incidence of product comigration. In this case, fractionating the highly heterogeneous mixture into discrete bands helped reduce signal suppression and detection bias. As a result, the corresponding MS data enabled the assignment of 248 products out of the possible 513 predicted from the 5'-UTR sequence, which afforded 100% sequence coverage. This figure represented a significant improvement over the 36 total products identified earlier under suboptimal conditions, which afforded only 57% coverage, or the 83 observed by direct infusion nanospray-MS (72%). These results provided a measure of the excellent potential of the technique to support the bottom-up characterization of progressively larger NA samples, such as putative NA therapeutics and mRNA vaccines.

Capillary electrophoresis-mass spectrometry for protein analyses under native conditions: Current progress and perspectives

Native mass spectrometry is a rapidly emerging technique for fast and sensitive structural analysis of protein constructs, maintaining the protein higher order structure. The coupling with electromigration separation techniques under native conditions enables the characterization of proteoforms and highly complex protein mixtures. In this review, we present an overview of current native CE-MS technology. First, the status of native separation conditions is described for capillary zone electrophoresis (CZE), affinity capillary electrophoresis (ACE), and capillary isoelectric focusing (CIEF), as well as their chip-based formats, including essential parameters such as electrolyte composition and capillary coatings. Further, conditions required for native ESI-MS of (large) protein constructs, including instrumental parameters of QTOF and Orbitrap systems, as well as requirements for native CE-MS interfacing are presented. On this basis, methods and applications of the different modes of native CE-MS are summarized and discussed in the context of biological, medical, and biopharmaceutical questions. Finally, key achievements are highlighted and concluded, while remaining challenges are pointed out.

Capillary electrophoresis in the analysis of therapeutic peptides-A review

Therapeutic peptides are a growing class of innovative drugs with high efficiency and a low risk of adverse effects. These biomolecules fall within the molecular mass range between that of small molecules and proteins. However, their inherent instability and potential for degradation underscore the importance of reliable and effective analytical methods for pharmaceutical quality control, therapeutic drug monitoring, and compliance testing. Liquid chromatography-mass spectrometry (LC-MS) has long time been the "gold standard" conventional method for peptide analysis, but capillary electrophoresis (CE) is increasingly being recognized as a complementary and, in some cases, superior, highly efficient, green, and cost-effective alternative technique. CE can separate peptides composed of different amino acids owing to differences in their net charge and size, determining their migration behavior in an electric field. This review provides a comprehensive overview of therapeutic peptides that have been used in the clinical environment for the last 25 years. It describes the properties, classification, current trends in development, and clinical use of therapeutic peptides. From the analytical point of view, it discusses the challenges associated with the analysis of therapeutic peptides in pharmaceutical and biological matrices, as well as the evaluation of CE as a whole and the comparison with LC methods. The article also highlights the use of microchip electrophoresis, nonaqueous CE, and nonconventional hydrodynamically closed CE systems and their applications. Overall, the article emphasizes the importance of developing new CE-based analytical methods to ensure the high quality, safety, and efficacy of therapeutic peptides in clinical practice.

MS-based glycomics and glycoproteomics methods enabling isomeric characterization

Glycosylation is one of the most significant and abundant posttranslational modifications in mammalian cells. It mediates a wide range of biofunctions, including cell adhesion, cell communication, immune cell trafficking, and protein stability. Also, aberrant glycosylation has been associated with various diseases such as diabetes, Alzheimer's disease, inflammation, immune deficiencies, congenital disorders, and cancers. The alterations in the distributions of glycan and glycopeptide isomers are involved in the development and progression of several human diseases. However, the microheterogeneity of glycosylation brings a great challenge to glycomic and glycoproteomic analysis, including the characterization of isomers. Over several decades, different methods and approaches have been developed to facilitate the characterization of glycan and glycopeptide isomers. Mass spectrometry (MS) has been a powerful tool utilized for glycomic and glycoproteomic isomeric analysis due to its high sensitivity and rich structural information using different fragmentation techniques. However, a comprehensive characterization of glycan and glycopeptide isomers remains a challenge when utilizing MS alone. Therefore, various separation methods, including liquid chromatography, capillary electrophoresis, and ion mobility, were developed to resolve glycan and glycopeptide isomers before MS. These separation techniques were coupled to MS for a better identification and quantitation of glycan and glycopeptide isomers. Additionally, bioinformatic tools are essential for the automated processing of glycan and glycopeptide isomeric data to facilitate isomeric studies in biological cohorts. Here in this review, we discuss commonly employed MS-based techniques, separation hyphenated MS methods, and software, facilitating the separation, identification, and quantitation of glycan and glycopeptide isomers.

Highly Efficient Separation of Ultratrace Radioactive Copper Using a Flow Electrolysis Cell

Preparing compounds containing the radioisotope ⁶⁴Cu for use in positron emission tomography cancer diagnostics is an ongoing area of research. In this study, a highly efficient separation method to recover ⁶⁴Cu generated by irradiating the target ⁶⁴Ni with a proton beam was developed by employing a flow electrolysis cell (FE). This system consists of (1) applying a reduction potential for the selective adsorption of ⁶⁴Cu from the target solution when dissolved in HCl and (2) recovering the ⁶⁴Cu deposited onto the carbon working electrode by desorbing it from the FE during elution with 10 mmol/L HNO₃, which applies an oxidation potential. The ⁶⁴Cu was selectively eluted at approximately 30 min under a flow rate of 0.5 mL/min from the injection to recovery. The newly developed flow electrolysis system can separate the femtomolar level of ultratrace radioisotopes from the larger amount of target metals as an alternative to conventional column chromatography.

Capillary Isoelectric Focusing: Mass Spectrometry Method for the Separation and Online Characterization of Monoclonal Antibody Charge Variants at Intact and Subunit Levels

Monoclonal antibodies (mAbs) are one of the most widely used types of protein therapeutics. Charge variants are important quality attributes for evaluating developability, activity, and safety for mAb therapeutics. Here, we report a novel online capillary isoelectric focusing-mass spectrometry (CIEF-MS) method for mAb charge variant analysis using an electrokinetically pumped sheath-flow nanospray ion source on a time-of-flight (TOF) MS with a pressure-assisted chemical mobilization. Key factors that enable online CIEF-MS include effective capillary electrophoresis-MS (CE-MS) interface with enhanced sensitivity, utilization of MS-friendly electrolytes, beneficial effects of glycerol that reduces non-CIEF electrophoretic mobility and limits band broadening, appropriate ampholyte type and concentration selection for balanced separation resolution and MS detection sensitivity, optimized sheath liquid composition to realize high-resolution CIEF separation and effective MS electrospray ionization, as well as judiciously selected CIEF running parameters. The fundamental premise of CIEF has been verified by the linear correlation between isoelectric point (pI) values and migration time using a mixture of pI markers. By achieving high separation resolutions that are similar as those obtained from imaged CIEF (iCIEF), this method successfully provides highly sensitive MS identification for intact mAb charge variants. Furthermore, a middle-up sample treatment workflow can be adopted to provide in-depth charge variant analysis at subunit level for mAbs with complex charge heterogeneity. The mAb subunit CIEF-MS reveals the source of charge variant with enhanced resolution on both CIEF separation and MS spectra. This novel CIEF-MS method is a valuable tool with distinct advantage for objective and accurate assessment of charge heterogeneity of protein therapeutics.

The Application of Metabolomics in Forensic Science with Focus on Forensic Toxicology and Time-of-Death Estimation

Recently, the diagnostic methods used by scientists in forensic examinations have enormously expanded. Metabolomics provides an important contribution to analytical method development. The main purpose of this review was to investigate and summarize the most recent applications of metabolomics in forensic science. The primary research method was an extensive review of available international literature in PubMed. The keywords “forensic” and “metabolomics” were used as search criteria for the PubMed database scan. Most authors emphasized the analysis of different biological sample types using chromatography methods. The presented review is a summary of recently published implementations of metabolomics in forensic science and types of biological material used and techniques applied. Possible opportunities for valuable metabolomics’ applications are discussed to emphasize the essential necessities resulting in numerous nontargeted metabolomics’ assays.

CE-MS for Proteomics and Intact Protein Analysis

This chapter aims to explore various parameters involved in achieving high-end capillary electrophoresis hyphenated to mass spectrometry (CE-MS) analysis of proteins, peptides, and their posttranslational modifications. The structure of the topics discussed in this book chapter is conveniently mapped on the scheme of the CE-MS system itself, starting from sample preconcentration and injection techniques and finishing with mass analyzer considerations. After going through the technical considerations, a variety of relevant applications for this analytical approach are presented, including posttranslational modifications analysis, clinical biomarker discovery, and its growing use in the biotechnological industry.

Peptidomics and Capillary Electrophoresis

Peptides play a crucial role in many vitally important functions of living organisms. The goal of peptidomics is the identification of the "peptidome," the whole peptide content of a cell, organ, tissue, body fluid, or organism. In peptidomic or proteomic studies, capillary electrophoresis (CE) is an alternative technique for liquid chromatography. It is a highly efficient and fast separation method requiring extremely low amounts of sample. In peptidomic approaches, CE is commonly combined with mass spectrometric (MS) detection. Most often, CE is coupled with electrospray ionization MS and less frequently with matrix-assisted laser desorption/ionization MS. CE-MS has been employed in numerous studies dealing with determination of peptide biomarkers in different body fluids for various diseases, or in food peptidomic research for the analysis and identification of peptides with special biological activities. In addition to the above topics, sample preparation techniques commonly applied in peptidomics before CE separation and possibilities for peptide identification and quantification by CE-MS or CE-MS/MS methods are discussed in this chapter.

Current applications of capillary electrophoresis-mass spectrometry for the analysis of biologically important analytes in urine (2017 to mid-2021): A review

Capillary electrophoresis coupled online with mass detection is a modern tool for analyzing wide ranges of compounds in complex samples, including urine. Capillary electrophoresis with mass spectrometry allows the separation and identification of various analytes spanning from small ions to high molecular weight protein complexes. Similarly to the much more common liquid chromatography‐mass spectrometry techniques, the capillary electrophoresis separation reduces the complexity of the mixture of analytes entering the mass spectrometer resulting in reduced ion suppression and a more straightforward interpretation of the mass spectrometry data. This review summarizes capillary electrophoresis with mass spectrometry studies published between the years 2017 and 2021, aiming at the determination of various compounds excreted in urine. The properties of the urine, including its diagnostical and analytical features and chemical composition, are also discussed including general protocols for the urine sample preparation. The mechanism of the electrophoretic separation and the instrumentation for capillary electrophoresis with mass spectrometry coupling is also included. This review shows the potential of the capillary electrophoresis with mass spectrometry technique for the analyses of different kinds of analytes in a complex biological matrix. The discussed applications are divided into two main groups (capillary electrophoresis with mass spectrometry for the determination of drugs and drugs of abuse in urine and capillary electrophoresis with mass spectrometry for the studies of urinary metabolome).

Investigating the position of the separation capillary and emitter tube tips in a nanoflow sheath-liquid CE-ESI-MS interface to decouple the ESI potential

Robust decoupling of the ESI potential from the separation potential in CE-ESI-MS interfaces is very important for the high performance of the CE-ESI-MS devices and their applications for highly sensitive analyses of ionogenic compounds. In this study, we utilize a nanoflow sheath-liquid CE-ESI-MS interface composed of a quartz emitter and a separation fused silica capillary treated by etching, which are threaded to cross coupling for sheath liquid and electrode connection. Specifically, we have tested the ability of the interface to decouple the ESI potential from the separation potential at different positions of the separation capillary and ESI emitter tube tips. The interface with the separation capillary tip protruding the emitter tip by 20 μm did not provide sufficient robustness. The real ESI potential (delivered as 2.0 kV from the independent high voltage power supply HV2) ranged from 2.1 kV to 4.5 kV depending on the applied separation voltage (12.0-20.0 kV, provided by the power supply HV1) and electric conductivity of the background electrolyte (BGE) used. The interface robustness was partially improved when the capillary tip was aligned with the emitter tip. However, the complete decoupling of the spray and separation potentials was achieved only when the capillary tip was retracted 20 μm inside the emitter. In this arrangement, the ESI potential was stable and independent of both the separation potential (voltage) and the BGE conductivity. Moreover, this setting provided better sensitivity for the CE-ESI-MS analysis of selected drugs and benzylpyridinium cations than the setup with the capillary tip aligned with or protruding the emitter tip.

Recent advances in isoelectric focusing of proteins and peptides

This review article describes the significant recent advances in Isoelectric Focusing from the period 2015-2020. The review highlights the principles and common challenges faced in Isoelectric Focusing as well as its applications. This review also details the recent advances in various modes of Isoelectric Focusing in various platforms and future directions for the technique.

Microfluidics for Peptidomics, Proteomics, and Cell Analysis

Microfluidics is the advanced microtechnology of fluid manipulation in channels with at least one dimension in the range of 1-100 microns. Microfluidic technology offers a growing number of tools for manipulating small volumes of fluid to control chemical, biological, and physical processes relevant to separation, analysis, and detection. Currently, microfluidic devices play an important role in many biological, chemical, physical, biotechnological and engineering applications. There are numerous ways to fabricate the necessary microchannels and integrate them into microfluidic platforms. In peptidomics and proteomics, microfluidics is often used in combination with mass spectrometric (MS) analysis. This review provides an overview of using microfluidic systems for peptidomics, proteomics and cell analysis. The application of microfluidics in combination with MS detection and other novel techniques to answer clinical questions is also discussed in the context of disease diagnosis and therapy. Recent developments and applications of capillary and microchip (electro)separation methods in proteomic and peptidomic analysis are summarized. The state of the art of microchip platforms for cell sorting and single-cell analysis is also discussed. Advances in detection methods are reported, and new applications in proteomics and peptidomics, quality control of peptide and protein pharmaceuticals, analysis of proteins and peptides in biomatrices and determination of their physicochemical parameters are highlighted.

Plastic in agricultural soils - A global risk for groundwater systems and drinking water supplies? - A review

The global plastic contamination is one of the major challenges facing mankind as plastic is ubiquitously present in all environmental compartments. In contrast to freshwater and marine environments, plastic contamination of agricultural soils was only recently subject to investigations although it represents a significant amount (14%) of the global plastic pollution. Of concern is the vertical migration of plastic particles in agricultural soils and plastic-induced enhancement of pesticide transport towards underlying groundwater systems. To assess the risk of the large plastic inventory in agricultural soils for groundwater systems and drinking water supplies, this review critically synthesizes the current knowledge of the plastic mobility and plastic-pesticide interactions in agricultural soils, identifies future research directions and evaluates associated analytical challenges. The reviewed studies provide consistent evidence for vertical migration of plastic in agricultural soils towards aquifer systems, especially for sub-micrometer sized plastic particles, analogously to the well-known migration of natural particles in the sub-micrometer range (colloids). The reviewed investigations also showed that plastic changes the sorption behavior of pesticides in agricultural soils and enhances their transport towards underlying groundwater systems. Hence, the deposited plastic in agricultural soils likely poses a major risk for underlying aquifers and drinking water supplies that rely on groundwater resources below farmlands to be contaminated by plastic and pesticides. This demonstrates that improved regulatory measures are necessary regarding the general usage of plastic in the farming process to protect aquifers and drinking water supplies from plastic and pesticide contamination and to avoid a potential human health hazard.

Recent Advances in Trace Bioanalysis by Capillary Electrophoresis

Recently, single cell analysis is becoming more and more important to elucidate cellular heterogeneity. Except for nucleic acid that can be amplified by PCR, the required technical level for single cell analysis is extremely high and the appropriate design of sample preparation and a sensitive analytical system is necessary. Capillary/microchip electrophoresis (CE/MCE) can separate biomolecules in nL-scale solution with high resolution, and it is highly compatible with trace samples like a single cell. Coupled with highly sensitive detectors such as laser-induced fluorescence and nano-electrospray ionization-mass spectrometry, zmol level analytes can be detected. For further enhancing sensitivity, online sample preconcentration techniques can be employed. By integrating these high-sensitive techniques, single cell analysis of metabolites, proteins, and lipids have been achieved. This review paper highlights successful research on CE/MCE-based trace bioanalysis in recent 10 years. Firstly, an overview of basic knowledge on CE/MCE including sensitivity enhancement techniques is provided. Applications to trace bioanalysis are then introduced with discussion on current issues and future prospects.

Electrospray ionization stability and concentration sensitivity in capillary electrophoresis-mass spectrometry using a flow-through microvial interface

Concentration sensitivity is a key performance indicator for analytical techniques including for capillary electrophoresis-mass spectrometry (CE-MS) with electrospray ionization (ESI). In this study, a flow-through microvial interface was used to couple CE with MS and improve the ESI stability and detection sensitivity. By infusing a peptide mixture through the interface into an MS detector at a typical flow rate for CE-MS analysis, the spatial region near the interface was mapped for MS signal intensity. When the sprayer tip was within a 6 × 6.5 × 5 mm region in front of the MS inlet, the ESI was stable with no significant loss of signal intensity for ions with m/z 239. Finite element simulations showed that the average electric field strength at the emitter tip did not change significantly with minor changes in emitter tip location. Experiments were conducted with four different mass spectrometer platforms coupled to CE via the flow-through microvial interface. Key performance indicators, that is, limit of detection (LOD) and linearity of calibration curves were measured for nine amino acids and five peptides. Inter- and intraday reproducibility were also tested. The results were shown to be suitable for quantification when internal standards were used.

Capillary Electrophoresis-Mass Spectrometry for Metabolomics: Possibilities and Perspectives

Capillary electrophoresis-mass spectrometry (CE-MS) is a very useful analytical technique for the selective and highly efficient profiling of polar and charged metabolites in a wide range of biological samples. Compared to other analytical techniques, the use of CE-MS in metabolomics is relatively low as the approach is still regarded as technically challenging and not reproducible. In this chapter, the possibilities of CE-MS for metabolomics are highlighted with special emphasis on the use of recently developed interfacing designs. The utility of CE-MS for targeted and untargeted metabolomics studies is demonstrated by discussing representative and recent examples in the biomedical and clinical fields. The potential of CE-MS for large-scale and quantitative metabolomics studies is also addressed. Finally, some general conclusions and perspectives are given on this strong analytical separation technique for probing the polar metabolome.

A Comparative Evaluation of Tools to Predict Metabolite Profiles From Microbiome Sequencing Data

Metabolomic analyses of human gut microbiome samples can unveil the metabolic potential of host tissues and the numerous microorganisms they support, concurrently. As such, metabolomic information bears immense potential to improve disease diagnosis and therapeutic drug discovery. Unfortunately, as cohort sizes increase, comprehensive metabolomic profiling becomes costly and logistically difficult to perform at a large scale. To address these difficulties, we tested the feasibility of predicting the metabolites of a microbial community based solely on microbiome sequencing data. Paired microbiome sequencing (16S rRNA gene amplicons, shotgun metagenomics, and metatranscriptomics) and metabolome (mass spectrometry and nuclear magnetic resonance spectroscopy) datasets were collected from six independent studies spanning multiple diseases. We used these datasets to evaluate two reference-based gene-to-metabolite prediction pipelines and a machine-learning (ML) based metabolic profile prediction approach. With the pre-trained model on over 900 microbiome-metabolome paired samples, the ML approach yielded the most accurate predictions (i.e., highest F1 scores) of metabolite occurrences in the human gut and outperformed reference-based pipelines in predicting differential metabolites between case and control subjects. Our findings demonstrate the possibility of predicting metabolites from microbiome sequencing data, while highlighting certain limitations in detecting differential metabolites, and provide a framework to evaluate metabolite prediction pipelines, which will ultimately facilitate future investigations on microbial metabolites and human health.

Two capillary approach for a multifunctional nanoflow sheath liquid interface for capillary electrophoresis-mass spectrometry

CE hyphenated to ESI-MS (CE-ESI-MS) is a well-established technique to analyze charged analytes in complex samples. Although various interfaces for CE-MS coupling are commercially available, the development of alternatives which combine sensitivity, simplicity, and robustness remains a topic of research. In this work, a nanoflow sheath liquid CE-MS interface with two movable capillaries inside a glass emitter is described. The setup enables a separation mode and a conditioning mode to guide the separation capillary effluent either into the electrospray or to the waste, respectively. This enables to exclude parts of the analysis from MS detection and unwanted matrix components reaching the mass spectrometer, comparable to divert valves in LC-MS coupling. Also, this function improves the overall robustness of the system by reduction of particles blocking the emitter. Preconditioning with electrospray interfering substances and even the application of coating materials for every analysis is enabled, even while the separation capillary is built into the interface with running electrospray. The functionality is demonstrated by analyses of heavy matrix bioreactor samples. Overall, this innovation offers a more convenient installation of the interface, improved handling with an extended lifetime of the emitter tips and additional functions compared to previous approaches, while keeping the higher sensitivity of nanoflow CE-MS-coupling.

Development of a novel sheathless CE-ESI-MS interface via a CO2 laser ablated opening

A new and easy to construct sheathless capillary electrophoresis electro spray ionization mass spectrometry (CE-ESI-MS) interface was developed that offers several advantages compared to traditional liquid junction interfaces. The fabrication of the device only requires a CO₂ laser engraver that most groups working with microfluids have access to. It only takes a few seconds to create a CO₂ laser ablated opening in the bare-fused silica capillaries and the opening can be placed as close as a few mm from the spray tip. The capillary is punctured through a silicone tube such that the opening is directly placed inside this tube, which also serves as a liquid reservoir for the make-up liquid. Electrical contact required for both CE separation and ESI is established via the liquid in this reservoir which is in contact with the electrode of an external high voltage power supply. The developed CE-ESI-MS interface is capable of analysing both small molecules and biomolecules such as peptides in physisorbed PEG polymer brush coated capillaries. Proof-of-principle of the interface was demonstrated by analysing a tryptic digest of BSA. Further, a range of drugs of abuse were also investigated. The examined small molecules (pethidine, nortriptyline, methadone, haloperidol and loperamide) have a quantification limit (LOQ) of 150 ng/mL and a detection limit (LOD) of 40 ng/mL (except for loperamide: LOD = 80 ng/mL). Finally, we used our novel CE-MS interface for the analysis of the Aβ40 peptide. This is a member of the beta-Amyloid peptide family, involved in the development of Alzheimer's disease. A LOQ of 9 μg/mL was obtained for Aβ40, corresponding to 23 fmoles in a sample volume of 11 nL.

A gold foil covered fused silica capillary tip as a sheathless interface for coupling capillary electrophoresis-mass spectrometry

A method for the preparation of an on-column ESI emitter used as the sheathless interface for coupling capillary electrophoresis (CE) with mass spectrometry (MS) was developed. The emitter was directly fabricated at the outlet end of the separation capillary which was etched with HF solution to a symmetrical tip. The tip was covered with a small piece of gold foil which was fixed by epoxy resin glue for electrical contact. Such a prepared ESI emitter can produce a stable ESI signal over the wide range of flow rate from 50 nL/min to 800 nL/min. The performance of the CE-MS with the sheathless interface was evaluated by using the separation of four alkaloids. It was found that the strong electroosmotic flow produced by the multiple polyelectrolyte coating on the capillary is necessary for maintaining a stable MS signal. Effect of the running buffer composition, concentration and the CE separation voltages on the ESI signal strength were investigated. The absolute detection limits for the alkaloids was determined as fmol level. Moreover, the CE-MS was applied for the analyses of trypsin digestion of cytochrome C and small molecular organic anions. The emitter performed very stable with a lifetime of at least 180 h.

Advances in the Analysis of Veterinary Drug Residues in Food Matrices by Capillary Electrophoresis Techniques

In the last years, the European Commission has adopted restrictive directives on food quality and safety in order to protect animal and human health. Veterinary drugs represent an important risk and the need to have sensitive and fast analytical techniques to detect and quantify them has become mandatory. Over the years, the availability of different modes, interfaces, and formats has improved the versatility, sensitivity, and speed of capillary electrophoresis (CE) techniques. Thus, CE represents a powerful tool for the analysis of a large variety of food matrices and food-related molecules with important applications in food quality and safety. This review focuses the attention of CE applications over the last decade on the detection of different classes of drugs (used as additives in animal food or present as contaminants in food products) with a potential risk for animal and human health. In addition, considering that the different sample preparation procedures have strongly contributed to CE sensitivity and versatility, the most advanced sample pre-concentration techniques are discussed here.

Recent trends of capillary electrophoresis-mass spectrometry in proteomics research

Progress in proteomics research has led to a demand for powerful analytical tools with high separation efficiency and sensitivity for confident identification and quantification of proteins, posttranslational modifications, and protein complexes expressed in cells and tissues. This demand has significantly increased interest in capillary electrophoresis-mass spectrometry (CE-MS) in the past few years. This review provides highlights of recent advances in CE-MS for proteomics research, including a short introduction to top-down mass spectrometry and native mass spectrometry (native MS), as well as a detailed overview of CE methods. Both the potential and limitations of these methods for the analysis of proteins and peptides in synthetic and biological samples and the challenges of CE methods are discussed, along with perspectives about the future direction of CE-MS. @ 2019 Wiley Periodicals, Inc. Mass Spec Rev 00:1-16, 2019.

Corona Isolation Method Matters: Capillary Electrophoresis Mass Spectrometry Based Comparison of Protein Corona Compositions Following On-Particle versus In-Solution or In-Gel Digestion

Increased understanding of the role of the nanomaterial protein corona in driving nanomaterial uptake into, and impacts on, cells and organisms, and the consequent need for characterization of the corona, has led to a flourishing of methods for isolation and analysis of the constituent proteins over the past decade. However, despite over 700 corona studies to date, very little is understood in terms of which methods provide the most precise and comprehensive characterization of the corona. With the increasing importance of the modeling of corona formation and its correlation with biological impacts, it is timely to properly characterize and validate the isolation approaches used to determine the protein corona. The current work introduces Capillary Electrophoresis with Electro Spray Ionization Mass Spectrometry (CESI-MS) as a novel method for protein corona characterizations and develops an on-particle tryptic digestion method, comparing peptide solubilization solutions and characterizing the recovery of proteins from the nanomaterial surface. The CESI-MS was compared to the gold standard nano-LC-MS for corona analysis and maintained a high degree of reproducibility, while increasing throughput by >3-fold. The on-particle digestion is compared to an in-solution digestion and an in-gel digestion of the protein corona. Interestingly, a range of different protein classes were found to be recovered to greater or lesser extents among the different methods. Apolipoproteins were detected at lower concentrations when a surfactant was used to solubilize peptides, whereas immunoglobulins in general have a high affinity for nanomaterials, and thus show lower recovery using on-particle digestion. The optimized on-particle digestion was validated using 6 nanomaterials and proved capable of recovering in excess of 97% of the protein corona. These are important factors to consider when designing corona studies and modeling corona formation and impacts, highlighting the significance of a comprehensive validation of nanomaterial corona analysis methods.

Recent advances in single cell manipulation and biochemical analysis on microfluidics

Single cell analysis has become of great interest with unprecedented capabilities for the systematic investigation of cell-to-cell variation in large populations. Rapid and multi-parametric analysis of intercellular biomolecules at the single-cell level is imperative for the improvement of early disease diagnosis and personalized medicine. However, the small size of cells and the low concentration levels of target biomolecules are critical challenges for single cell analysis. In recent years, microfluidic platforms capable of handling small-volume fluid have been demonstrated to be powerful tools for single cell analysis. In addition, microfluidic techniques allow for precise control of the localized microenvironment, which yield more accurate outcomes. Many different microfluidic techniques have been greatly improved for highly efficient single-cell manipulation and highly sensitive detection over the past few decades. To date, microfluidics-based single cell analysis has become the hot research topic in this field. In this review, we particularly highlight the advances in this field during the past three years in the following three aspects: (1) microfluidic single cell manipulation based on microwells, micropatterns, droplets, traps and flow cytometric methods; (2) detection methods based on fluorescence, mass spectrometry, electrochemical, and polymerase chain reaction-based analysis; (3) applications in the fields of small molecule detection, protein analysis, multidrug resistance analysis, and single cell sequencing with droplet microfluidics. We also discuss future research opportunities by focusing on key performances of throughput, multiparametric target detection and data processing.

Capillary electrophoresis of small ions and molecules in less conventional human body fluid samples: A review

In recent years, advances in sensitive analytical techniques have encouraged the analysis of various compounds in biological fluids. While blood serum, blood plasma and urine still remain the golden standards in clinical, toxicological and forensic science, analyses of other body fluids, such as breast milk, exhaled breath condensate, sweat, saliva, amniotic fluid, cerebrospinal fluid, or capillary blood in form of dried blood spots are becoming more popular. This review article focuses on capillary electrophoresis and microchip electrophoresis of small ions and molecules (e.g. inorganic cations/anions, basic/acidic drugs, small acids/bases, amino acids, peptides and other low molecular weight analytes) in various less conventional human body fluids and hopes to stimulate further interest in the field.

Recent advances in capillary electrophoresis-mass spectrometry: Instrumentation, methodology and applications

Capillary electrophoresis (CE) offers fast and high-resolution separation of charged analytes from small injection volumes. Coupled to mass spectrometry (MS), it represents a powerful analytical technique providing (exact) mass information and enables molecular characterization based on fragmentation. Although hyphenation of CE and MS is not straightforward, much emphasis has been placed on enabling efficient ionization and user-friendly coupling. Though several interfaces are now commercially available, research on more efficient and robust interfacing with nano-electrospray ionization (ESI), matrix-assisted laser desorption/ionization (MALDI) and inductively coupled plasma mass spectrometry (ICP) continues with considerable results. At the same time, CE-MS has been used in many fields, predominantly for the analysis of proteins, peptides and metabolites. This review belongs to a series of regularly published articles, summarizing 248 articles covering the time between June 2016 and May 2018. Latest developments on hyphenation of CE with MS as well as instrumental developments such as two-dimensional separation systems with MS detection are mentioned. Furthermore, applications of various CE-modes including capillary zone electrophoresis (CZE), nonaqueous capillary electrophoresis (NACE), capillary gel electrophoresis (CGE) and capillary isoelectric focusing (CIEF) coupled to MS in biological, pharmaceutical and environmental research are summarized.

Coupling of CE-MS for protein and peptide analysis

The review is focused on the latest developments in the analysis of proteins and peptides by capillary electrophoresis techniques coupled to mass spectrometry. First, the methodology and instrumentation are overviewed. In this section, recent progress in capillary electrophoresis with mass spectrometry interfaces and capillary electrophoresis with matrix-assisted laser desorption/ionization is mentioned, as well as separation tasks. The second part is devoted to applications-mainly bottom-up and top-down proteomics. It is obvious that capillary electrophoresis with mass spectrometry methods are well suited for peptide and protein analysis (proteomic research) and it is described how these techniques are complementary and not competitive with the often used liquid chromatography with mass spectrometry methods.

Combination of liquid-based column separations with surface-enhanced Raman spectroscopy

Surface-enhanced Raman spectroscopy is a constantly developing analytical method providing not only high-sensitive quantitative but also qualitative information on an analyte. Thus, it is reasonable that it has been tested as a promising detection method in column separations. Although its implementation in analytical separations is not widespread, some surprising results, like enormous signal enhancement and demonstrations of single-molecule identifications, proved in only a few special examples, indicate the potential of the method. The high detection sensitivity and selectivity would be of paramount importance in trace analyses of biologically relevant molecules in complex matrices. However, the combination of surface-enhanced Raman spectroscopy with column separation methods brings two principal issues. Interactions of analytes with metal substrates can cause deteriorations of separations and the detection can be affected by background electrolytes or elution agents. Thus, in principle, this review is on the experimental and methodological solutions to these problems. First, theoretical and practical aspects of Raman scattering, and excitation of surface plasmon in colloid suspensions of nanoparticles and on planar nanostructured substrates are briefly explained. Advances in experimental arrangements of on-line and at-line couplings with column liquid phase separation methods, including microfluidic devices, are described together with chosen analytical applications.