Influence of particle properties on the wall region in packed capillaries

A logarithmic law for the velocity- and retention-dependency of the eddy dispersion in chromatographic columns

Applying the recently introduced patchwork model for porous media, we present a new step forward in the modelling of eddy dispersion in chromatographic columns. The logarithmic law describing the velocity dependency emerging from this patchwork model is supplemented with a retention factor dependency via first principles modelling of the variations in flow resistance and retention capacity caused by the packing disorder. Furthermore, it is shown the derived expression is also able to fit the eddy dispersion originating from the wall effect on the packing. When applied to literature data of eddy dispersion, the newly introduced logarithmic law has a goodness of fit that is at least equal to that of Knox' empirical power law (R2>0.98). The main difference is that, whereas Knox' power law requires a separate fit for each component due to the retention factor dependency, the present model simultaneously fits all plate height curves measured on one chromatographic column, using only two parameters with a clear physical meaning.

Factors affecting therapeutic protein purity and yield during chromatographic purification

Therapeutic proteins are recombinant proteins generated through recombinant DNA technology and have attracted a great deal of interest in numerous applications, including pharmaceutical, cosmetic, human and animal health, agriculture, food, and bioremediation. Producing therapeutic proteins on a large scale, mainly in the pharmaceutical industry, necessitates a cost-effective, straightforward, and adequate manufacturing process. In industry, a protein separation technique based mainly on protein characteristics and modes of chromatography will be applied to optimize the purification process. Typically, the downstream process of biopharmaceutical operations may involve multiple chromatography phases that require the use of large columns pre-packed with resins that must be inspected before use. Approximately 20% of the proteins are assumed to be lost at each purification stage during the production of biotherapeutic products. Hence, to produce a high quality product, particularly in the pharmaceutical industry, the correct approach and understanding of the factors influencing purity and yield during purification are necessary.

Reversed-Phase Liquid Chromatography of Peptides for Bottom-Up Proteomics: A Tutorial

The performance of the current bottom-up liquid chromatography hyphenated with mass spectrometry (LC-MS) analyses has undoubtedly been fueled by spectacular progress in mass spectrometry. It is thus not surprising that the MS instrument attracts the most attention during LC-MS method development, whereas optimizing conditions for peptide separation using reversed-phase liquid chromatography (RPLC) remains somewhat in its shadow. Consequently, the wisdom of the fundaments of chromatography is slowly vanishing from some laboratories. However, the full potential of advanced MS instruments cannot be achieved without highly efficient RPLC. This is impossible to attain without understanding fundamental processes in the chromatographic system and the properties of peptides important for their chromatographic behavior. We wrote this tutorial intending to give practitioners an overview of critical aspects of peptide separation using RPLC to facilitate setting the LC parameters so that they can leverage the full capabilities of their MS instruments. After briefly introducing the gradient separation of peptides, we discuss their properties that affect the quality of LC-MS chromatograms the most. Next, we address the in-column and extra-column broadening. The last section is devoted to key parameters of LC-MS methods. We also extracted trends in practice from recent bottom-up proteomics studies and correlated them with the current knowledge on peptide RPLC separation.

The use of predictive models to develop chromatography-based purification processes

Chromatography is the workhorse of biopharmaceutical downstream processing because it can selectively enrich a target product while removing impurities from complex feed streams. This is achieved by exploiting differences in molecular properties, such as size, charge and hydrophobicity (alone or in different combinations). Accordingly, many parameters must be tested during process development in order to maximize product purity and recovery, including resin and ligand types, conductivity, pH, gradient profiles, and the sequence of separation operations. The number of possible experimental conditions quickly becomes unmanageable. Although the range of suitable conditions can be narrowed based on experience, the time and cost of the work remain high even when using high-throughput laboratory automation. In contrast, chromatography modeling using inexpensive, parallelized computer hardware can provide expert knowledge, predicting conditions that achieve high purity and efficient recovery. The prediction of suitable conditions in silico reduces the number of empirical tests required and provides in-depth process understanding, which is recommended by regulatory authorities. In this article, we discuss the benefits and specific challenges of chromatography modeling. We describe the experimental characterization of chromatography devices and settings prior to modeling, such as the determination of column porosity. We also consider the challenges that must be overcome when models are set up and calibrated, including the cross-validation and verification of data-driven and hybrid (combined data-driven and mechanistic) models. This review will therefore support researchers intending to establish a chromatography modeling workflow in their laboratory.

An improved method for sensitive quantification of isoprenoid diphosphates in the astaxanthin-accumulating Haematococcus pluvialis

A sensitive method has been established to simultaneously determine the concentrations of isopentenyl pyrophosphate (IPP), geranyl diphosphate (GPP), farnesyl diphosphate (FPP) and geranylgeranyl diphosphate (GGPP) in H. pluvialis under different environments. This method increased the extraction efficiency of isoprenoid diphosphates through releasing isoprenoid diphosphates using Tissue Lyser. This is the first report on the efficient extraction method of metabolites in H. pluvialis cells, being suitable for all algae and plants with thick cell wall. The concentrations of isoprenoid diphosphates were measured on poroshell EC-C18 column by UHPLC-MS/MS with the LODs of 0.015, 0.027, 0.022 and 0.076 pmol for DMAPP, GPP, FPP and GGPP, respectively. It is the most sensitive method for the determination of isoprenoid diphosphates in any sample to date. Using this method, the profile of isoprenoid diphosphates was analyzed and cisoid isomers of FPP and GGPP, (Z, Z)-FPP and (Z, Z, Z-GGPP) were found firstly in H. pluvialis.

Investigation of stationary phases performance for eicosanoids profiling in RP-HPLC

Eicosanoids - oxidative derivatives from arachidonic acid - represent biologically active lipid mediators in inflammatory processes. Different analytical methods treat eicosanoid analysis. Among which, reverse phase liquid chromatography figures as the appropriate method for eicosanoid profiling. RP-HPLC for eicosanoid analysis is often conducted on C18 columns. Some studies focused on profiling one family of eicosanoids; others considered all eicosanoid families. In both cases, co-elution remained a major issue and detection in mass spectrometry partially resolves this problem. In fact, the mass transitions used to monitor eicosanoid species are not specific enough and many isobars can be listed. For this, optimizing the RP-HPLC separation remains important. Based on the parameter F_s - deriving from the hydrophobic-subtraction model - and radar plots, we chose columns with different selectivities. The hydrophobic-subtraction model guided our interpretation of molecular interactions between eicosanoids and stationary phases. We founded our approach for selectivity optimization on peak capacity per minute and time needed values. Herein, we screened seven stationary phases and evaluated their chromatographic performances in RP-HPLC. Stationary phases presented different chemistry, type of silica, length, and particle size. Superficially porous particle columns registered better chromatographic profiles than classical stationary phases; and columns with embedded polar group did not serve our purpose. The stationary phase Accucore C30 - even being the least retentive - revealed the best selectivity and efficiency, and recorded the shorter duration for eicosanoid analysis.

Segmented Microfluidics-Based Packing Technology for Chromatographic Columns

Nanoflow liquid chromatography-mass spectrometry (NanoLC-MS) has become the method of choice for the analysis of complex biological systems, especially when the available sample amount is limited. The preparation of high-performance capillary columns for nanoLC use is still a technical challenge. Here, we report a segmented microfluidic method for the preparation of packed capillary columns, where liquid segments were used as soft, dynamic, and well-dispersed slurry reservoirs for carrying and delivering micrometer packing particles. Based on this microfluidic packing technology, the column bed was assembled layer-by-layer at a 50 μm resolution, and ultralong capillary columns of 3, 5, and 10 m were fabricated in such a manner. The microfluidically packed columns demonstrated excellent separation efficiencies of 116 000 plates/m. The higher efficiencies obtained at higher slurry concentrations also indicate that a high-quality packed bed can be obtained without sacrificing the packing speed. Kinetic performance limit analysis shows that the microfluidic packed columns have higher peak capacity production efficiency in the high-resolution region, presenting an improved separation impedance of 2800, which is significantly better than columns packed with the conventional slurry packing method. In comparison with a commercial nanoLC column, a 5 m long microfluidic packed column was evaluated for proteomic analysis using a standard HeLa protein digest and presented 261% improvement in peptide identification capability, resulting in significantly enhanced protein identification confidence.

Insights into the intraparticle morphology of dendritic mesoporous silica nanoparticles from electron tomographic reconstructions

HYPOTHESIS

Although many synthetic pathways allow to fine-tune the morphology of dendritic mesoporous silica nanoparticles (DMSNs), the control of their particle size and mesopore diameter remains a challenge. Our study focuses on either increasing the mean particle size or adjusting the pore size distribution, changing only one parameter (particle or pore size) at a time. The dependence of key morphological features (porosity; pore shape and pore dimensions) on radial distance from the particle center has been investigated in detail.

EXPERIMENTS

Three-dimensional reconstructions of the particles obtained by scanning transmission electron microscopy (STEM) tomography were adapted as geometrical models for the quantification of intraparticle morphologies by radial porosity and chord length distribution analyses. Structural properties of the different synthesized DMSNs have been complementary characterized using TEM, SEM, nitrogen physisorption, and dynamic light scattering.

FINDINGS

The successful independent tuning of particle and pore sizes of the DMSNs could be confirmed by conventional analysis methods. Unique morphological features, which influence the uptake and release of guest molecules in biomedical applications, were uncovered from analyzing the STEM tomography-based reconstructions. It includes the quantification of structural hierarchy, identification of intrawall openings and pores, as well as the distinction of pore shapes (conical vs. cylindrical).

Performance of nanoflow liquid chromatography using core-shell particles: A comparison study

Due to its unique structure, core-shell material has presented significantly improved chromatographic performance in comparison with conventional totally porous material. This has been well demonstrated in the analytical column format, e.g. 4.6 mm i.d. columns. In the proteomics field, there is always a demand for high resolution microseparation tools. In order to explore core-shell material's potential in proteomics-oriented microseparations, we investigated chromatographic performance of core-shell material in a nanoLC format, as well as its resolving power for protein digests. The results show core-shell nanoLC columns have similar van Deemter curves to the totally porous particle-packed nanoLC columns. For 100 µm i.d. capillary columns, the core-shell material does not have significantly better dynamics. However, both core-shell and totally porous particle-packed nanoLC columns have shown high efficiencies: plate heights of ~11 µm, equivalent to 90000 plates per meter, have been achieved with 5 µm particles. Using a 60 cm long core-shell nanoLC column, 72000 plates were realized in an isocratic separation of neutral compounds. For a 15 cm long nanoLC column, a maximum peak capacity of 220 has been achieved in a 5 hour gradient separation of protein digests, indicating the high resolving power of core-shell nanoLC columns. With a standard HeLa cell lysate as the sample, 2546 proteins were identified by using the core-shell nanoLC column, while 2916 proteins were identified by using the totally porous particle-packed nanoLC column. Comparing the two sets of proteomics data, it was found that 1830 proteins were identified by both columns, while 1086 and 716 proteins were uniquely identified by using totally porous and core-shell particle-packed nanoLC columns, respectively, suggesting their complementarity in nanoLC-MS based proteomics.

Fundamental to achieving fast separations with high efficiency: A review of chromatography with superficially porous particles

Types of particles have been fundamental to LC separation technology for many years. Originally, LC columns were packed with large-diameter (>100 μm) calcium carbonate, silica gel, or alumina particles that prohibited fast mobile-phase speeds because of the slow diffusion of sample molecules inside deep pores. During the birth of HPLC in the 1960s, superficially porous particles (SPP, ≥30 μm) were developed as the first high-speed stationary-phase support structures commercialized, which permitted faster mobile-phase flowrates due to the fast movement of sample molecules in/out of the thin shells. These initial SPPs were displaced by smaller totally porous particles (TPP) in the mid-1970s. But SPP history repeated when UHPLC emerged in the 2000s. Stationary-phase support structures made from sub-3-μm SPPs were introduced to chromatographers in 2006. The initial purpose of this modern SPP was to enable chromatographers to achieve fast separations with high efficiency using conventional HPLCs. Later, the introduction of sub-2-μm SPPs with UHPLC instruments pushed the separation speed and efficiency to a very fast zone. This review aims at providing readers a comprehensive and up-to-date view on the advantages of SPP materials over TPPs historically and theoretically from the material science angle.

Through-pore polymerization in polar high-performance liquid chromatography columns allowing scanning electron microscopy based imaging of the packing order

To allow an enhanced understanding of the order in packed HPLC columns, in this work a methodology for immobilizing native polar silica particles is developed based on the polymerization of a methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDMA) as a cross-linker in the interstitial pores of HPLC columns. Subsequent mechanical cutting then allows scanning electron microscopy (SEM) based imagery of cross-sections of the packed bed. In this way, the packing efficiency of home-made and commercial HPLC columns with 4.6 mm inner diameter and 150 mm length comprising the same packing material of 5 µm silica particles are compared. The methodology is developed for native silica used in e.g. hydrophilic interaction liquid chromatography (HILIC) and in normal phase LC. In order to confirm the feasibility of the developed methodology, the conventional methods for the evaluation of column, efficiency and porosity, are also employed. The obtained porosity information is compared and showed the same trend with the external porosity measurements obtained via inverse size exclusion approach, illustrating its potential application to study the micro-heterogeneity of packed HPLC columns and to guide the optimization of the packing process of HPLC columns.

Application of chiral chromatography in radiopharmaceutical fields: A review

Chiral column chromatography (CCC) is a revolutionary analytical methodology for the enantioseparation of novel positron emission tomography (PET) tracers in the primary stages of drug development. Due to the different behaviors of tracer enantiomers (e.g. toxicity, metabolism and side effects) in administrated subjects, their separation and purification is a challenging endeavor. Over the last three decades, different commercial chiral columns have been applied for the enantioseparation of PET-radioligand (PET-RL) or radiotracers (PET-RT), using high-performance liquid chromatography (HPLC). The categorization and reviewing of them is a vital topic. This review presents a brief overview of advances, applications, and future prospectives of CCC in radiopharmaceutical approaches. In addition, the effective chromatographic parameters and degravitation trends to enhance enantioseparation resolution are addressed. Moreover, the application and potential of chiral super fluidical chromatography (CSFC) as an alternative for enantioseparation in the field of radiopharmaceutical is discussed. Finally, the crucial application challenges of CCC are explained and imminent tasks are suggested.

Fundamental Properties of Packing Materials for Liquid Chromatography

The high performance of chemically-modified silica gel packing materials is based on the utilization of pure silica gels. Earlier silica gels used to be made from inorganic silica; however, nowadays, silica gels are made from organic silanes. The surface smoothness and lack of trace metals of new silica gels permits easy surface modifications (chemical reactions) and improves the reproducibility and stability. Sharpening peak symmetry is based on developing better surface modification methods (silylation). Typical examples can be found in the chromatography of amitriptyline for silanol testing and that of quinizarin for trace metal testing. These test compounds were selected and demonstrated sensitive results in the measurement of trace amounts of either silanol or trace metals. Here, we demonstrate the three-dimensional model chemical structures of bonded-phase silica gels with surface electron density for easy understanding of the molecular interaction sites with analytes. Furthermore, a quantitative explanation of hydrophilic and hydrophobic liquid chromatographies was provided. The synthesis methods of superficially porous silica gels and their modified products were introduced.

Cyclofructans as Chiral Selectors: An Overview

Cyclofructans are cyclic oligosaccharides made of β-2,1-linked fructofuranose units. They have been utilized as chiral selectors, usually after derivatization, with high-performance liquid chromatography (HPLC), gas chromatography (GC), capillary electrophoresis (CE), and supercritical fluid chromatography (SFC). The focus herein will be directed to their development and applications as chiral selectors in various chiral separation techniques. Discussion of their use in hydrophilic liquid interaction chromatography (HILIC) will be limited. Their use in liquid chromatography, especially their improvements with the use of superficially porous particles (SPPs) will be emphasized. Method parameters and future directions are also discussed.

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.

Bed morphological features associated with an optimal slurry concentration for reproducible preparation of efficient capillary ultrahigh pressure liquid chromatography columns

Column wall effects and the formation of larger voids in the bed during column packing are factors limiting the achievement of highly efficient columns. Systematic variation of packing conditions, combined with three-dimensional bed reconstruction and detailed morphological analysis of column beds, provide valuable insights into the packing process. Here, we study a set of sixteen 75μm i.d. fused-silica capillary columns packed with 1.9μm, C18-modified, bridged-ethyl hybrid silica particles slurried in acetone to concentrations ranging from 5 to 200mg/mL. Bed reconstructions for three of these columns (representing low, optimal, and high slurry concentrations), based on confocal laser scanning microscopy, reveal morphological features associated with the implemented slurry concentration, that lead to differences in column efficiency. At a low slurry concentration, the bed microstructure includes systematic radial heterogeneities such as particle size-segregation and local deviations from bulk packing density near the wall. These effects are suppressed (or at least reduced) with higher slurry concentrations. Concomitantly, larger voids (relative to the mean particle diameter) begin to form in the packing and increase in size and number with the slurry concentration. The most efficient columns are packed at slurry concentrations that balance these counteracting effects. Videos are taken at low and high slurry concentration to elucidate the bed formation process. At low slurry concentrations, particles arrive and settle individually, allowing for rearrangements. At high slurry concentrations, they arrive and pack as large patches (reflecting particle aggregation in the slurry). These processes are discussed with respect to column packing, chromatographic performance, and bed microstructure to help reinforce general trends previously described. Conclusions based on this comprehensive analysis guide us towards further improvement of the packing process.

Effect of pore-size optimization on the performance of polysaccharide-based superficially porous chiral stationary phases for the separation of enantiomers in high-performance liquid chromatography

Our earlier studies on the preparation of chiral stationary phases (CSP) based on superficially porous (or core-shell) silica (SPS) particles for the separation of enantiomers in HPLC have provided proof to the advantages of such sorbents. In particular, higher enantioselectivity was observed with the columns packed with superficially porous CSP compared to the columns packed with fully-porous (FP) silica-based CSPs at comparable content of chiral selector (polysaccharide derivative) in CSP. Also, less dependence of plate height on mobile phase flow rate and higher plate numbers and resolution calculated per unit time (i.e. speed of separation) were observed with SPS-based CSPs. Thirty years of CSP development have demonstrated that wide-pore silica has to be used as a support for large molecular weight chiral selectors such as the ones based on polysaccharides. In this study the effect of pore size of the core-shell silica support and of other experimental factors on column performance is demonstrated. Reduced plate heights in the range 1.4-1.5 were obtained, as well as highly effective baseline separations of enantiomers were observed with analysis times of less than 15s.

Larger voids in mechanically stable, loose packings of 1.3μm frictional, cohesive particles: Their reconstruction, statistical analysis, and impact on separation efficiency

Lateral transcolumn heterogeneities and the presence of larger voids in a packing (comparable to the particle size) can limit the preparation of efficient chromatographic columns. Optimizing and understanding the packing process provides keys to better packing structures and column performance. Here, we investigate the slurry-packing process for a set of capillary columns packed with C18-modified, 1.3μm bridged-ethyl hybrid porous silica particles. The slurry concentration used for packing 75μm i.d. fused-silica capillaries was increased gradually from 5 to 50mg/mL. An intermediate concentration (20mg/mL) resulted in the best separation efficiency. Three capillaries from the set representing low, intermediate, and high slurry concentrations were further used for three-dimensional bed reconstruction by confocal laser scanning microscopy and morphological analysis of the bed structure. Previous studies suggest increased slurry concentrations will result in higher column efficiency due to the suppression of transcolumn bed heterogeneities, but only up to a critical concentration. Too concentrated slurries favour the formation of larger packing voids (reaching the size of the average particle diameter). Especially large voids, which can accommodate particles from>90% of the particle size distribution, are responsible for a decrease in column efficiency at high slurry concentrations. Our work illuminates the increasing difficulty of achieving high bed densities with small, frictional, cohesive particles. As particle size decreases interparticle forces become increasingly important and hinder the ease of particle sliding during column packing. While an optimal slurry concentration is identified with respect to bed morphology and separation efficiency under conditions in this work, our results suggest adjustments of this concentration are required with regard to particle size, surface roughness, column dimensions, slurry liquid, and external effects utilized during the packing process (pressure protocol, ultrasound, electric fields).

Topological analysis of non-granular, disordered porous media: determination of pore connectivity, pore coordination, and geometric tortuosity in physically reconstructed silica monoliths

Different approaches are applied and compared, which are universally applicable to quantify pore coordination, pore and pore-throat connectivity, and geometric tortuosity.

Evaluation of 5 µm Superficially Porous Particles for Capillary and Microfluidic LC Columns

Large-size (4–5 µm) superficially porous particles yield lower plate heights (e.g., the minimal reduced plate height or h_min ≈ 1.5) than fully porous particles of a similar size when packed into large-bore columns. This property allows for better chromatographic performance without the higher pressures required for smaller particles. This study explores the use of such particles in microfluidic LC columns where materials and fitting pressure limits can constrain the size of particle used. The theoretically predicted performance improvements compared to fully porous particles were not demonstrated in capillary columns (with h_min ≈ 2 for both particle types), in agreement with previous studies that examined smaller superficially porous particles. Microfluidic columns were then compared to capillary columns. Capillary columns significantly outperformed microfluidic columns due to imperfections imposed by microfluidic channel asymmetry and world-to-chip connection at the optimal flow rate; however, superficially porous particles packed in microfluidic LC columns had flatter plate height versus flow rate curves indicating potential for better performance at high reduced velocities.

Gone in seconds: praxis, performance, and peculiarities of ultrafast chiral liquid chromatography with superficially porous particles

A variety of brush-type chiral stationary phases (CSPs) were developed using superficially porous particles (SPPs). Given their high efficiencies and relatively low back pressures, columns containing these particles were particularly advantageous for ultrafast "chiral" separations in the 4-40 s range. Further, they were used in all mobile phase modes and with high flow rates and pressures to separate over 60 pairs of enantiomers. When operating under these conditions, both instrumentation and column packing must be modified or optimized so as not to limit separation performance and quality. Further, frictional heating results in axial thermal gradients of up to 16 °C and radial temperature gradients up to 8 °C, which can produce interesting secondary effects in enantiomeric separations. It is shown that the kinetic behavior of various CSPs can differ from one another as much as they differ from the well-studied C18 reversed phase media. Three additional interesting aspects of this work are (a) the first kinetic evidence of two different chiral recognition mechanisms, (b) a demonstration of increased efficiencies at higher flow rates for specific separations, and