Recent developments in microcolumn liquid chromatography

Nano liquid chromatography, an updated review

Low flow chromatography has a rich history of innovation but has yet to reach widespread implementation in bioanalytical applications. Improvements in pump technology, microfluidic connections, and nano-electrospray sources for mass spectrometry have laid the groundwork for broader application, and innovation in this space has accelerated in recent years. This article reviews the instrumentation used for nano-flow liquid chromatography , the types of columns employed, and strategies for multi-dimensionality of separations, which is key to the future state of the technique to the high-throughput needs of modern bioanalysis. An update of the current applications where nano-LC is widely used, such as proteomics and metabolomics, is discussed. But the trend towards biopharmaceutical development of increasingly complex, targeted, and potent therapeutics for the safe treatment of disease drives the need for ultimate selectivity and sensitivity of our analytical platforms for targeted quantitation in a regulated space. The selectivity needs are best addressed by mass spectrometric detection, especially at high resolutions, and exquisite sensitivity is provided by nano-electrospray ionization as the technology continues to evolve into an accessible, robust, and easy to use platform.

Dissolved organic matter in the deep TALDICE ice core: A nano-UPLC-nano-ESI-HRMS method

Trace organic compounds in deep ice cores supply important paleoclimatic information. Untargeted analyses of dissolved organic matter provide an overview of molecular species in ice samples however, sample volumes usually required for these analyses are generally not available from deep ice cores. Here, we developed an analytical method using a nano-UPLC-nano-ESI-HRMS to detect major molecular species in ice cores. Samples (4 µL) from the TALos Dome Ice CorE (TALDICE), allowed investigating molecular species across a range of depths including during glacial and interglacial periods. We detected 317 chemical species that were tentatively assigned to fatty acids, hydroxy fatty acids and their degradation products (oxo-fatty acids and dicarboxylic acids), as well as oxidation byproducts of isoprene and monoterpenes. These compounds indicate that the main sources of the organic fraction are microbes as well as primary and secondary aerosols. Interglacial samples encompass a wide range of species including compounds from the oxidation of isoprene and monoterpenes as well as unsaturated fatty acids, while the glacial samples contained less diverse species. This difference may be due to decreased temperatures during the glacial period inhibiting terrestrial vegetation growth and increasing the sea ice extent, thereby weakening the emission sources.

Nano-liquid chromatography for enantiomers separation of baclofen by using vancomycin silica stationary phase

The chiral separation of baclofen (Bac) was obtained by nano-liquid chromatography tandem mass spectrometry (nano-LC-MS/MS) using a 100 μm I.D. fused silica capillary column packed with silica particles chemically modified with vancomycin. Various experimental parameters, such as composition (buffer concentration, water content, organic modifier) and pH of the mobile phase and sample solvent were investigated for method optimization. In order to increase the sensitivity an on-column focusing procedure was applied. Acceptable separation of Bac enantiomers was obtained in less than 11 min eluting in isocratic mode, with 90:10 MeOH/water (v/v) containing 10 mM ammonium acetate at pH 4.5. These optimized experimental conditions were applied to the analysis of human plasma samples spiked with racemic mixture of Bac. The use of a Buckypaper disc as sorbent membrane allows one to recover both enantiomers with yields ≥ 65%. The method was fully validated, following the identification criteria of the European Commission Decision 2002/657/EC.

Development and evaluation of silica-based lectin microcolumns for glycoform analysis of alpha1-acid glycoprotein

Silica-based lectin microcolumns were developed and optimized for the separation and analysis of glycoform fractions in alpha₁-acid glycoprotein (AGP) based on both the degree of branching and level of fucosylation. Concanavalin A (Con A) and Aleuria Aurantia lectin (AAL) were immobilized onto HPLC-grade silica by reductive amination and packed into 2.1 mm i.d. × 5.0 cm microcolumns. Factors examined for these microcolumns include their protein content, binding capacity, binding strength and band-broadening under isocratic conditions (Con A) or step elution conditions (AAL) and in the presence of various flow rates or temperatures. These factors were examined by using experiments based on frontal analysis, zonal elution, peak profiling and peak decay analysis. Up to 200 μg AGP could be loaded onto a Con A microcolumn and provide linear elution conditions, and 100 μg AGP could be applied to an AAL microcolumn. The final conditions for separating retained and non-retained AGP glycoform fractions on a Con A microcolumn used a flow rate of 50 μL min^-1 and a temperature of 50 °C, which gave a separation of these fractions within 20 min or less. The final conditions for an AAL microcolumn included a flow rate of 0.75 mL min^-1, a temperature of 50 °C, and the use of 2.0 mM l-fucose as a competing agent for elution, giving a separation of non-retained and retained AGP glycoforms in 6 min or less. The inter-day precisions were ±0.7-4.0% or less for the retention times of the AGP glycoforms and ±2.2-3.0% or less for their peak areas.

Rugged Large Volume Injection for Sensitive Capillary LC-MS Environmental Monitoring

A rugged and high throughput capillary column (cLC) LC-MS switching platform using large volume injection and on-line automatic filtration and filter back-flush (AFFL) solid phase extraction (SPE) for analysis of environmental water samples with minimal sample preparation is presented. Although narrow columns and on-line sample preparation are used in the platform, high ruggedness is achieved e.g., injection of 100 non-filtrated water samples did not result in a pressure rise/clogging of the SPE/capillary columns (inner diameter 300 μm). In addition, satisfactory retention time stability and chromatographic resolution were also features of the system. The potential of the platform for environmental water samples was demonstrated with various pharmaceutical products, which had detection limits (LOD) in the 0.05–12.5 ng/L range. Between-day and within-day repeatability of selected analytes were <20% RSD.

Recent advances in capillary ultrahigh pressure liquid chromatography

In the twenty years since its initial demonstration, capillary ultrahigh pressure liquid chromatography (UHPLC) has proven to be one of most powerful separation techniques for the analysis of complex mixtures. This review focuses on the most recent advances made since 2010 towards increasing the performance of such separations. Improvements in capillary column preparation techniques that have led to columns with unprecedented performance are described. New stationary phases and phase supports that have been reported over the past decade are detailed, with a focus on their use in capillary formats. A discussion on the instrument developments that have been required to ensure that extra-column effects do not diminish the intrinsic efficiency of these columns during analysis is also included. Finally, the impact of these capillary UHPLC topics on the field of proteomics and ways in which capillary UHPLC may continue to be applied to the separation of complex samples are addressed.

Rapid determination of nucleotides in infant formula by means of nano-liquid chromatography

A rapid method for the quantification of five ribonucleotides 5'- monophophates (adenosine, cytidine, guanosine, inosine, uridine, 5'-monophosphate), in infant formula, has been proposed using nano-LC. To separate the studied compounds, capillary columns packed with different C18-based stationary phases were investigated. All the columns tested were laboratory prepared. The experiments were performed in ion-pairing RP chromatographic mode using tetrabutylammonium hydroxide as ion-pairing reagent. The method was developed using a core-shell XB-C18 capillary column with a mobile phase consisting of 5% v/v methanol and 95% v/v 100 mM ammonium formate, pH 8, containing 20 mM tetrabutylammonium hydroxide. All compounds were baseline resolved in less than 5 min with a flow rate of 500 nL/min in isocratic elution mode. Nucleotides were detected at 260 nm. Analytical validation parameters were evaluated. The RSD values for intraday and interday repeatability for retention time and peak area were <2.4 and 4.2%, respectively. The method linearity was good (R(2) < 0.9995) for the studied compounds. LOD and limit of quantitation were 0.25 and 0.50 μg/mL, respectively. The method was applied to the determination of nucleotides in infant formula, subjected to a centrifugal ultrafiltration process, prior their analysis. The amounts found were in agreement to the labeled contents.

Ultrafast Polyphenol Metabolomics of Red Wines Using MicroLC-MS/MS

The taste and quality of red wine are determined by its highly complex mixture of polyphenols and many other metabolites. No single method can fully cover the full metabolome, but even for polyphenols and related compounds, current methods proved inadequate. We optimized liquid chromatography resolution and sensitivity using 1 mm i.d. columns with microLC pumps and compared data-dependent to data-independent (SWATH) MS/MS acquisitions. A high-throughput microLC-MS method was developed with a 4 min gradient at 0.05 mL/min flow rate on a Kinetex C18 column and Sciex TripleTOF mass spectrometry. Using the novel software MS-DIAL, we structurally annotated 264 compounds including 165 polyphenols in six commercial red wines by accurate mass MS/MS matching. As proof of concept, multivariate statistics revealed the difference in the metabolite profiles of the six red wines, and regression analysis linked the polyphenol contents to the taste of the red wines.

Quantitative online sheath-flow surface enhanced Raman spectroscopy detection for liquid chromatography

Sheath-flow surface-enhanced Raman spectroscopy (SERS) was used for online detection and quantification of small molecules separated by liquid chromatography.

Evolution in miniaturized column liquid chromatography instrumentation and applications: An overview

The purpose of this article is to underline the miniaturized LC instrumental system and describe the evolution of commercially available systems by discussing their advantages and drawbacks. Nowadays, there are already many miniaturized LC systems available with a great variety of pump design, interface and detectors as well as efficient columns technologies and reduced connections devices. The solvent delivery systems are able to drive the mobile phase without flow splitters and promote gradient elution using either dual piston reciprocating or syringe-type pumps. The mass spectrometry as detection system is the most widely used detection system; among many alternative ionization sources direct-EI LC-MS is a promising alternative to APCI. In addition, capillary columns are now available showing many possibilities of stationary phases, inner diameters and hardware materials. This review provides a discussion about miniaturized LC demonstrating fundamentals and instrumentals' aspects of the commercially available miniaturized LC instrumental system mainly nano and micro LC formats. This review also covers the recent developments and trends in instrumentation, capillary and nano columns, and several applications of this very important and promising field.

Nano-LC in proteomics: recent advances and approaches

In proteomics, nano-LC is arguably the most common tool for separating peptides/proteins prior to MS. The main advantage of nano-LC is enhanced sensitivity, as compounds enter the MS in more concentrated bands. This is particularly relevant for determining low abundant compounds in limited samples. Nano-LC columns can produce peak capacities of 1000 or more, and very narrow columns can be used to perform proteomics of 1000 cells or less. Also, nano-LC can be coupled with online add-ons such as selective trap columns or enzymatic reactors, for faster and more automated analysis. Nano-LC is today an established tool for research laboratories; but can nano-LC-based systems soon be ready for more routine settings, such as in clinics?

MicroQuEChERS-nanoliquid chromatography-nanospray-tandem mass spectrometry for the detection and quantification of trace pharmaceuticals in benthic invertebrates

Due to industrialization and the use of chemical products in everyday life, various types of drugs and pesticides are present in our environment, which threaten and cause negative impacts on aquatic ecosystems. The consequences of these pollutants are gradually becoming visible. Recent evidence confirms that long term exposure to environmental pharmaceutical concentrations can induce adverse effects in aquatic vertebrates and invertebrates such as reproductive impairments and collapse wild populations. Consequently, one of the challenges of environmental science is to evaluate the associated risks. In this context, a new methodology has been developed using nano-LC-nano-ESI MS/MS to quantify traces of two pharmaceuticals (a neuropharmaceutical drug, fluoxetine, and an anticonvulsant drug, carbamazepine) in two molluscs, Potamopyrgus antipodarum and Valvata piscinalis, which are both prosobranch gastropods. A simple and quick extraction method was developed based on a modified and miniaturized version of the QuEChERS method. The procedure involves the extraction of approximately 10 mg of wet mollusc tissue by 500 µL of a mixture of acetonitrile/water/hexane (50/20/30) and 100 mg of buffer salt. Thus, the extraction step was carried out on an individual scale. The sensitivity of this method allowed for the detection of levels as low as 18 ng/g and 128 ng/g for carbamazepine and fluoxetine, respectively, with recoveries of greater than 85% for the two targeted compounds. This method was then applied to both gastropod species exposed to fluoxetine under laboratory conditions. The results provide evidence of bioaccumulation in both P. antipodarum and V. piscinalis and reveal the inter-species differences.

Nano-LC-MS/MS for the quantitation of prostanoids in immune cells

Prostanoids, derivatives of arachidonic acid, are involved in inflammation and immune reactions. To understand the role of prostanoids produced by diverse immune cells, a highly sensitive quantitation method for prostaglandin E2 (PGE2), prostaglandin D2 (PGD2), 6-keto prostaglandin F1α (6-keto PGF1α), prostaglandin F2α (PGF2α), and thromboxane B2 (TXB2) by means of nano-liquid chromatography-tandem mass spectrometry has been developed. It was validated according to the guidelines of the Food and Drug Administration (FDA) in terms of linearity, precision, accuracy, recovery, stability, and lower limit of quantitation (LLOQ). The LLOQ were 25 pg/mL in the injected solution (75 fg on column (o.c.)) for PGE2 and PGD2 and 37.5 pg/mL (112.5 fg on column) for 6-keto PGF1α, PGF2α, and TXB2, respectively. It was successfully applied to murine mast cells isolated from paws after zymosan injection and to CD4(+) and CD8(+) T lymphocytes from blood of sensitized versus non-sensitized mice in context of a delayed type hypersensitivity model. About 5,000 (T cells) to 40,000 (mast cells) cells were sufficient for quantitation. In the mast cells, the production of PGE2 increased at a significantly higher extent than the synthesis of the other prostanoids. The T lymphocytes did not show any difference in prostanoid production, no matter whether they were obtained from sensitized mice or non-sensitized mice.

Incorporating high-pressure electroosmotic pump and a nano-flow gradient generator into a miniaturized liquid chromatographic system for peptide analysis

We integrate a high-pressure electroosmotic pump (EOP), a nanoflow gradient generator, and a capillary column into a miniaturized liquid chromatographic system that can be directly coupled with a mass spectrometer for proteomic analysis. We have recently developed a low-cost high-pressure EOP capable of generating pressure of tens of thousands psi, ideal for uses in miniaturized HPLC. The pump worked smoothly when it was used for isocratic elutions. When it was used for gradient elutions, generating reproducible gradient profiles was challenging; because the pump rate fluctuated when the pump was used to pump high-content organic solvents. This presents an issue for separating proteins/peptides since high-content organic solvents are often utilized. In this work, we solve this problem by incorporating our high-pressure EOP with a nano-flow gradient generator so that the EOP needs only to pump an aqueous solution. With this combination, we develop a capillary-based nano-HPLC system capable of performing nano-flow gradient elution; the pump rate is stable, and the gradient profiles are reproducible and can be conveniently tuned. To demonstrate its utility, we couple it with either a UV absorbance detector or a mass spectrometer for peptide separations.

Optimizing the selective recognition of protein isoforms through tuning of nanoparticle hydrophobicity

We demonstrate that ligand hydrophobicity can be used to increase affinity and selectivity of binding between monolayer-protected cationic gold nanoparticles and β-lactoglobulin protein isoforms containing two amino acid mutations.

Capillary liquid chromatography fraction collection and postcolumn reaction using segmented flow microfluidics

A challenge for capillary LC (cLC) is fraction collection and the manipulation of fractions from microscale columns. An emerging approach is the use of segmented flow or droplet technology to perform such tasks. In this work, a fraction collection and postcolumn reaction system based on segmented flow was developed for the gradient cLC of proteins. In the system, column effluent and immiscible oil are pumped into separate arms of a tee resulting in regular fractions of effluent segmented by oil. Fractions were generated at 1 Hz corresponding to 5 nL volumes. The fraction collection rate was high enough to generate over 30 fractions per peak and preserve chromatographic resolution achieved for a five-protein test mixture. The resulting fractions could be stored and subsequently derivatized for fluorescence detection by pumping them into a second tee where naphthalene dicarboxyaldehyde, a fluorogenic reagent, was pumped into a second arm and added to each fraction. Proteins were derivatized within the droplets enabling postcolumn fluorescence detection of the proteins. The experiments demonstrate that fraction collection from cLC by segmented flow can be extended to proteins. Further, they illustrate a potential workflow for protein analysis based on postcolumn derivatization for fluorescence detection.

Bioanalytical LC separation techniques for quantitative analysis of free amino acids in human plasma

The quantitative analysis of free amino acids in human plasma has become an important and essential analysis parameter in different areas of life sciences. Free amino acid concentrations in human plasma samples are generally determined by means of GC or LC after chemical derivatization followed by UV, fluorescent or MS detection of the amino acid derivatives. Derivatization of free amino acids is done either pre- or post-column, and the amino acid derivatives obtained posess improved chromatographic behavior, increased detection sensitivity and selectivity compared with non-derivatized free amino acids. This work gives an overview of different chemical derivatization methods applied and their liquid separation techniques in bioanalytical assays for quantitative free amino acid analysis in human plasma samples. Important plasma preparation procedures, pre- and post-column derivatization, and different LC separation techniques are presented.

Evaluation of different extraction approaches for the determination of phenolic compounds and their metabolites in plasma by nanoLC-ESI-TOF-MS

Sample preparation is an important step for the determination of phenolic compounds in biological samples. Different extraction methods have been tested to determine phenolic compounds and their metabolites in plasma by nano-liquid chromatography coupled to electrospray ionisation-time-of-flight mass spectrometry (nanoLC-ESI-TOF-MS). The sample treatment optimisation was performed using commercial foetal bovine serum spiked with representative phenolic standards, namely naringenin, luteolin, verbascoside, apigenin, rutin, syringic acid and catechin. Different protein-precipitation conditions were evaluated as well as enzymatic digestion with trypsin and solid-phase extraction using different phases such as C-18, ABN and ENV+, working at different pH values. The optimum extraction procedure consisted of a previous protein-precipitation step using HCl 200 mmol/L in methanol for 2.5 h at 50 °C followed by a solid-phase extraction using C-18 cartridges at pH 2.5. This procedure was finally applied to the plasma of rats overfed with a phenolic-rich Lippia citriodora extract. These samples were analysed by nanoLC-ESI-TOF-MS, enabling the identification of five compounds previously found in the administered L. citriodora extract and one metabolite.

Microbore polypropylene capillary channeled polymer (C-CP) fiber columns for rapid reversed-phase HPLC of proteins

The performance of microbore columns with polypropylene (PP) capillary-channeled polymer (C-CP) fibers as the support/stationary phase for separation of macromolecules has been investigated. Polypropylene C-CP fibers (40 μm diameter) were packed in fluorinated ethylene propylene (FEP) tubing of inner diameter 0.8 mm and lengths of 40, 60, 80, and 110 cm. The performance of PP fiber packed microbore columns (peak width, peak capacity, and resolution) was evaluated for separation of a three-protein mixture of ribonuclease A, cytochrome c, and transferrin under reversed-phase gradient conditions. The low backpressure characteristics of C-CP fiber columns enable operation at high linear velocities (up to 75 mm s(-1) at 1.5 mL min(-1)). In contrast with the performance of other phases, such velocities enable enhanced resolution of the three-protein mixture, because peak widths decrease with velocity. Increased column length resulted in increased resolution, because the peak widths remained essentially constant, although retention times increased. In addition, it was found that the peak capacity increased with column length and linear velocity. Radial compression of the microbore tubing enhanced the homogeneity of the packing and, thereby, separation efficiency and resolution. Radial compression of columns resulted in a decrease in the interstitial fraction (~5%), but increased resolution of ~14% between ribonuclease A and cytochrome c. Even so, a linear velocity of 75 mm s(-1) required a backpressure of 9.5 MPa only. It is clear that the fluid and solute-transport properties of the C-CP fiber microbore columns afford far better performance than is obtainable by use of standard format columns. The ability to achieve high separation efficiencies, rapidly and with low volume flow rates, holds promise for high-capacity protein separations in proteomics applications.

An overview of recent advances in HPLC instrumentation

This review highlights the fundamentals and the most prominent advances in the field of HPLC instrumentation over the last decades. Fundamental aspects and practical considerations of column switching, conventional (heart-cut) and comprehensive two-dimensional LC are presented. Different aspects of microcolumn- and nanoliquid-chromatography are reviewed. Recent progress in column technology and the demands and developments in instrumentation and accessories for miniaturized LC are also discussed. In the field of miniaturization, particularly in chip-based nano-LC systems, some aspects on micro-fluidic chip fabrication, using particle-packed HPLC microchips or polymer-based monoliths, are addressed. An introduction to ultra performance LC (UPLC) is also presented.

Online nanoliquid chromatography-mass spectrometry and nanofluorescence detection for high-resolution quantitative N-glycan analysis

The characterization of the repertoire of glycans at the quantitative and qualitative levels on cells and glycoproteins is a necessary step to the understanding of glycan functions in biology. In addition, there is an increasing demand in the field of biotechnology for the monitoring of glycosylation of recombinant glycoproteins, an important issue with regard to their safety and biological activity. The enzymatic release followed by fluorescent derivatization of glycans and separation by normal phase high-performance liquid chromatography (HPLC) has proven for many years to be a powerful approach to the quantification of glycans. Characterization of glycans has classically been performed by mass spectrometry (MS) with external standardization. Here, we report a new method for the simultaneous quantification and characterization of the N-glycans on glycoproteins without the need for external standardization. This method, which we call glycan nanoprofiling, uses nanoLC-coupled electrospray ionization (ESI)-MS with an intercalated nanofluorescence reader and provides effective single glycan separation with subpicomolar sensitivity. The method relies on the isolation and coumaric derivatization of enzymatically released glycans collected by solid phase extraction with porous graphitized carbon and their separation over polyamide-based nanoHPLC prior to serial nanofluorescence and nanoelectrospray mass spectrometric analysis. Glycan nanoprofiling is a broadly applicable and powerful approach that is sufficient to identify and quantify many glycan oligomers in a single run. Glycan nanoprofiling was successfully applied to resolve the glycans of monoclonal antibodies, showing that this method is a fast and sensitive alternative to available methods.

Quantitative neuroproteomics: classical and novel tools for studying neural differentiation and function

Mechanisms underlying neural stem cell proliferation, differentiation and maturation play a critical role in the formation and wiring of neuronal connections. This process involves the activation of multiple serial events, which guide the undifferentiated cells to different lineages via distinctive developmental programs, forming neuronal circuits and thus shaping the adult nervous system. Furthermore, alterations within these strictly regulated pathways can lead to severe neurological and psychiatric diseases. In this framework, the investigation of the high dynamic protein expression changes and other factors affecting protein functions, for example post-translational modifications, the alterations of protein interaction networks, is of pivotal importance for the understanding of the molecular mechanisms responsible for cell differentiation. More recently, proteomic studies in neuroscience ("neuroproteomics") are receiving increased interest for the primary understanding of the regulatory networks underlying neuronal differentiation processes. Besides the classical two-dimensional-based proteomic strategies, the emerging platforms for LC-MS shotgun proteomic analysis hold great promise in unraveling the molecular basis of neural stem cell differentiation. In this review, recent advancements in label-free LC-MS quantitative neuroproteomics are highlighted as a new tool for the study of neural differentiation and functions, in comparison to mass spectrometry-based labeling approaches. The more commonly used protein profiling strategies and model systems for the analysis of neural differentiation are also discussed, along with the challenging proteomic approaches aimed to analyze the nervous system-specific organelles, the neural cells secretome and the specific protein interaction networks.

Analysis of anthocyanins in commercial fruit juices by using nano-liquid chromatography-electrospray-mass spectrometry and high-performance liquid chromatography with UV-vis detector

Nano-LC and conventional HPLC techniques were applied for the analysis of anthocyanins present in commercial fruit juices using a capillary column of 100 μm id and a 2.1 mm id narrow-bore C(18) column. Analytes were detected by UV-Vis at 518 nm and ESI-ion trap MS with HPLC and nano-LC, respectively. Commercial blueberry juice (14 anthocyanins detected) was used to optimize chromatographic separation of analytes and other analysis parameters. Qualitative identification of anthocyanins was performed by comparing the recorded mass spectral data with those of published papers. The use of the same mobile phase composition in both techniques revealed that the miniaturized method exhibited shorter analysis time and higher sensitivity than narrow-bore chromatography. Good intra-day and day-to-day precision of retention time was obtained in both methods with values of RSD less than 3.4 and 0.8% for nano-LC and HPLC, respectively. Quantitative analysis was performed by external standard curve calibration of cyanidin-3-O-glucoside standard. Calibration curves were linear in the concentration ranges studied, 0.1-50 and 6-50 μg/mL for HPLC-UV/Vis and nano-LC-MS, respectively. LOD and LOQ values were good for both methods. In addition to commercial blueberry juice, qualitative and quantitative analysis of other juices (e.g. raspberry, sweet cherry and pomegranate) was performed. The optimized nano-LC-MS method allowed an easy and selective identification and quantification of anthocyanins in commercial fruit juices; it offered good results, shorter analysis time and reduced mobile phase volume with respect to narrow-bore HPLC.