Band broadening in size-exclusion chromatography of polydisperse samples

Improved Performance of UHPLC–MS Hyphenated Systems

An ultrahigh-pressure liquid chromatography–mass spectrometry (UHPLC–MS) research prototype instrument was built to improve the resolution power and the usability of conventional LC–MS hyphenated instruments for routine analyses in pharmaceutical applications. The improved characteristics of this UHPLC–MS system include: 1) the dramatic reduction of post-column sample dispersion; 2) the adoption of vacuum jacketed columns (VJC) for the reduction of undesirable radial temperature gradients across the column diameter; and 3) the presence of a column outlet end nut heater to refocus the distorted peaks prior to analyte ionization. The benefits of each of these added features are analyzed with a rigorous approach from a peak broadening perspective. A 2x improvement in peak capacities recorded with this prototype UHPLC–MS system compared to a standard system (Acquity UHPLC I-class/Xevo TQ-S) is illustrated for the gradient separation of seven small pharmaceutical compounds using a 2.1 mm x 100 mm column packed with sub-2-μm core-shell particles (1.6 μm Acquity UHPLC Cortecs C18 column).

A general model for the ideal chain length distributions of polymers made with reversible deactivation

A general model is developed for the distribution of polymers made with reversible deactivation. The model is applied to a range of experimental systems including RAFT, cationic and ATRP.

Fourier transformation liquid chromatography: increasing sensitivity by a factor of 50

To turn liquid chromatography into a Fourier transformation technique a continuous sinusoidal sample concentration profile is developed, which increases the sensitivity. The analytes can be characterized by evaluating the phase angle and magnitude.

Online μSEC2-nRPLC-MS for Improved Sensitivity of Intact Protein Detection of IEF-Separated Nonhuman Primate Cerebrospinal Fluid Proteins

Proteoform-resolved information, obtained by top-down (TD) "intact protein" proteomics, is expected to contribute substantially to the understanding of molecular pathogenic mechanisms and, in turn, identify novel therapeutic and diagnostic targets. However, the robustness of mass spectrometry (MS) analysis of intact proteins in complex biological samples is hindered by the high dynamic range in protein concentration and mass, protein instability, and buffer complexity. Here, we describe an evolutionary step for intact protein investigations through the online implementation of tandem microflow size-exclusion chromatography with nanoflow reversed-phase liquid chromatography and MS (μSEC2-nRPLC-MS). Online serial high-/low-pass SEC filtration overcomes the aforementioned hurdles to intact proteomic analysis through automated sample desalting/cleanup and enrichment of target mass ranges (5-155 kDa) prior to nRPLC-MS. The coupling of μSEC to nRPLC is achieved through a novel injection volume control (IVC) strategy of inserting protein trap columns, pre- and post-μSEC columns, to enable injection of dilute samples in high volumes without loss of sensitivity or resolution. Critical characteristics of the approach are tested via rigorous investigations on samples of varied complexity and chemical background. Application of the platform to cerebrospinal fluid (CSF) prefractionated by OFFGEL isoelectric focusing drastically increases the number of intact mass tags (IMTs) detected within the target mass range (5-30 kDa) in comparison to one-dimensional nRPLC-MS with approximately 100× less CSF than previous OFFGEL studies. Furthermore, the modular design of the μSEC2-nRPLC-MS platform is robust and promises significant flexibility for large-scale TDMS analysis of diverse samples either directly or in concert with other multidimensional fractionation steps.

Molecular Exchange Kinetics in Complex Coacervate Core Micelles: Role of Associative Interaction

Molecular exchange dynamics between spherical complex coacervate core micelles (C3Ms) are documented using time-resolved small-angle neutron scattering measurements (TR-SANS), and the effects of salt concentration, type of charges, and core block polydispersity to the chain exchange are quantified. Isotopically labeled block copolyelectrolytes were prepared by postpolymerization modification of two nearly identical poly(ethylene oxide-b-allyl glycidyl ether), one with normal and the other with deuterated PEO blocks (i.e., hPEO-PAGE and dPEO-PAGE). The observed rates at multiple salt concentrations are consolidated using time-salt superposition shift factors representing chain exchange rates and analyzed. Our comprehensive analytical relaxation function based on the sticky-Rouse model and the thermodynamic barrier for core block extraction successfully describes the molecular exchange kinetics between the isotopically labeled C3Ms. We believe this work provides fundamental design criteria for C3Ms with engineered chain exchange dynamics.

Detection and phenotyping of extracellular vesicles by size exclusion chromatography coupled with on-line fluorescence detection

New methods for quantifying extracellular vesicles (EVs) in complex biofluids are critically needed. We report the development of a new technology combining size exclusion chromatography (SEC), a commonly used EV purification technique, with fluorescence detection of specifically labelled EVs. The resulting platform, Flu-SEC, demonstrates a linear response to concentration of specific EVs and could form the basis of a system with phenotyping capability. Flu-SEC was validated using red blood cell derived EVs (REVs), which provide an ideal EV model with monodisperse size distribution and high EV concentration. Microfluidic Resistive Pulse Sensing (MRPS) was used to accurately determine the size distribution and concentration of REVs. Anti-CD235a antibody, specific to glycophorin A, and the more general wheat germ agglutinin (WGA), were selected to label REVs. The results show the quantitative power of Flu-SEC: a highly linear fluorescence response over a wide range of concentrations. Moreover, the Flu-SEC technique reports the ratio of EV-bound and free-antibody molecules, an important metric for determining optimal labelling conditions for other applications. Flu-SEC represents an orthogonal tool to single-particle fluorescent methods such as flow cytometry and fluorescent NTA, for the quantification and phenotyping of EVs.

Strengths and limitations of size exclusion chromatography for investigating single chain folding – current status and future perspectives

Synthetic approaches for Single-Chain Nanoparticles (SCNPs) developed rapidly during the last decade, opening a multitude of avenues for the design of functional macromolecular chains able to collapse into defined nanoparticles. However, the analytical evaluation of the SCNP formation process still requires critical improvements.

An optimized SEC-SAXS system enabling high X-ray dose for rapid SAXS assessment with correlated UV measurements for biomolecular structure analysis

A new optimized size exclusion chromatography small-angle X-ray scattering (SEC-SAXS) system for biomolecular SAXS at the Australian Synchrotron SAXS/WAXS beamline has been developed. The compact configuration reduces sample dilution to maximize sensitivity. Coflow sample presentation allows an 11-fold increase in flux on sample without capillary fouling, improving throughput and data quality, which are now primarily limited by the full flux available on the beamline. Multi-wavelength fibre optic UV analysis in close proximity to the X-ray beam allows for accurate concentration determination for samples with known UV extinction coefficients and thus estimation of the molecular weight of the scattering particle from the forward X-ray scattering intensity. Fast-flow low-volume SEC columns provide sample throughput competitive with batch concentration series measurements, albeit with a concomitant reduction of potential resolution relative to lower flow rates and larger SEC columns. The performance of the system is demonstrated using a set of model proteins, and its utility to solve various challenges is illustrated with a diverse suite of protein samples. These developments increase the quality and rigor of SEC-SAXS analysis and open new avenues for biomolecular solution SEC-SAXS studies that have been challenged by low sample yields, temporal instability, radiation sensitivity and complex mixtures.

Quantifying the Heterogeneity of Chemical Structures in Complex Charged Polymers through the Dispersity of Their Distributions of Electrophoretic Mobilities or of Compositions

The complexity of synthetic and natural polymers used in industrial and medical applications is expanding; thus, it becomes increasingly important to improve and develop methods for their molecular characterization. Free-solution capillary electrophoresis is a robust technique for the separation and characterization of both natural and synthetic complex charged polymers. In the case of polyelectrolytes, free-solution capillary electrophoresis is in the "critical conditions" (CE-CC): it allows their separation by factors other than molar mass for molar masses typically higher than 20000 g/mol. This method is thus complementary to size-exclusion chromatography (SEC). SEC is widely used to determine molar mass distributions and their dispersities. Utilizing CE-CC, an analogous calculation of dispersity based on the distributions of electrophoretic mobilities was derived and the heterogeneity of composition or branching in different polysaccharides or synthetic polymers was obtained in a number of experimental cases. Calculations are based on a ratio of moments and could therefore be compared to simulations of polymerization processes, in analogy to the work performed on molar mass distributions. Among four possible types of dispersity, the most precise values were obtained with the calculation analogous with the dispersity of molar mass distribution Mw/Mn. In addition, the dispersity value allows conclusions based on a single value: the closer the dispersity is to 1, the more homogeneous the polymer is in terms of composition or branching. This approach allows the analysis of dispersity of important molecular attributes of polymers other than molar mass and aims at improving the overall molecular characterization of both synthetic and natural polymers. The dispersity can also be monitored online while performing a chemical reaction within the CE instrument.

Using light scattering to evaluate the separation of polydisperse nanoparticles

The analysis of natural and otherwise complex samples is challenging and yields uncertainty about the accuracy and precision of measurements. Here we present a practical tool to assess relative accuracy among separation protocols for techniques using light scattering detection. Due to the highly non-linear relationship between particle size and the intensity of scattered light, a few large particles may obfuscate greater numbers of small particles. Therefore, insufficiently separated mixtures may result in an overestimate of the average measured particle size. Complete separation of complex samples is needed to mitigate this challenge. A separation protocol can be considered improved if the average measured size is smaller than a previous separation protocol. Further, the protocol resulting in the smallest average measured particle size yields the best separation among those explored. If the differential in average measured size between protocols is less than the measurement uncertainty, then the selected protocols are of equivalent precision. As a demonstration, this assessment metric is applied to optimization of cross flow (V(x)) protocols in asymmetric flow field flow fractionation (AF(4)) separation interfaced with online quasi-elastic light scattering (QELS) detection using mixtures of polystyrene beads spanning a large size range. Using this assessment metric, the V(x) parameter was modulated to improve separation until the average measured size of the mixture was in statistical agreement with the calculated average size of particles in the mixture. While we demonstrate this metric by improving AF(4) V(x) protocols, it can be applied to any given separation parameters for separation techniques that employ dynamic light scattering detectors.

Determination of the molecular weight of low-molecular-weight heparins by using high-pressure size exclusion chromatography on line with a triple detector array and conventional methods

The evaluation of weight average molecular weight (Mw) and molecular weight distribution represents one of the most controversial aspects concerning the characterization of low molecular weight heparins (LMWHs). As the most commonly used method for the measurement of such parameters is high performance size exclusion chromatography (HP-SEC), the soundness of results mainly depends on the appropriate calibration of the chromatographic columns used. With the aim of meeting the requirement of proper Mw standards for LMWHs, in the present work the determination of molecular weight parameters (Mw and Mn) by HP-SEC combined with a triple detector array (TDA) was performed. The HP-SEC/TDA technique permits the evaluation of polymeric samples by exploiting the combined and simultaneous action of three on-line detectors: light scattering detectors (LALLS/RALLS); refractometer and viscometer. Three commercial LMWH samples, enoxaparin, tinzaparin and dalteparin, a γ-ray depolymerized heparin (γ-Hep) and its chromatographic fractions, and a synthetic pentasaccharide were analysed by HP-SEC/TDA. The same samples were analysed also with a conventional HP-SEC method employing refractive index (RI) and UV detectors and two different chromatographic column set, silica gel and polymeric gel columns. In both chromatographic systems, two different calibration curves were built up by using (i) γ-Hep chromatographic fractions and the corresponding Mw parameters obtained via HP-SEC/TDA; (ii) the whole γ-Hep preparation with broad Mw dispersion and the corresponding cumulative distribution function calculated via HP-SEC/TDA. In addition, also a chromatographic column calibration according to European Pharmacopoeia indication was built up. By comparing all the obtained results, some important differences among Mw and size distribution values of the three LMWHs were found with the five different calibration methods and with HP-SEC/TDA method. In particular, the detection of the lower molecular weight components turned out to be the most critical aspect. Whereas HP-SEC/TDA may underestimate species under 2 KDa when present in low concentration, other methods appeared to emphasize their content.

Development of a chemically sensitive online SEC detector based on FTIR spectroscopy

A new FTIR–SEC coupling method provides correlated information about the molecular weight distribution and the chemical composition and has the potential to be applied as a standard SEC detector.

Size-Exclusion Chromatography for the Analysis of Protein Biotherapeutics and their Aggregates

In recent years, the use and number of biotherapeutics has increased significantly. For these largely protein-based therapies, the quantitation of aggregates is of particular concern given their potential effect on efficacy and immunogenicity. This need has renewed interest in size-exclusion chromatography (SEC). In the following review we will outline the history and background of SEC for the analysis of proteins. We will also discuss the instrumentation for these analyses, including the use of different types of detectors. Method development for protein analysis by SEC will also be outlined, including the effect of mobile phase and column parameters (column length, pore size). We will also review some of the applications of this mode of separation that are of particular importance to protein biopharmaceutical development and highlight some considerations in their implementation.

Size-separation characterization of starch and glycogen for biosynthesis-structure-property relationships

Starch and glycogen are highly branched polymers of glucose of great importance to humans in managing and mitigating nutrition-related diseases, especially diabetes and obesity, and in industrial uses, for example in food and paper-making. Size-separation characterization using multiple-detection size-exclusion chromatography (SEC, also known as gel-permeation chromatography, GPC) is able to furnish substantial amounts of information on the relationships between the biosynthesis, processing, structure, and properties of these biopolymers, and achieves superior characterization for use in industrial product and process improvements. Multi-detector SEC is able to give much more information about structure than simple averages such as total molecular weight or size; the detailed information yielded by this technique has already given new information on important biosynthesis-structure-property reactions, and has considerable potential in this field in the future. However, it must be used with care to avoid artifacts arising from incomplete dissolution of the substrate and shear scission during separation. It is also essential in interpreting data to appreciate that this size-separation technique can only ever give size distributions, never true molecular weight distributions. Other size-separation techniques, particularly field-flow fractionation, require substantial technical development to be used on undegraded native starches.

How much does band broadening adulterate results deduced from chromatograms measured by size-exclusion chromatography really?

A number of polystyrene samples and standards were measured with several column combinations which differed in their extent of band broadening, sigma(BB). Comparison of the derived chain length distributions showed in some cases good agreement even despite strong distinctions in the determined sigma(BB) values. The calculated number and weight averages of the samples were almost identical in most cases for the column combinations used. Furthermore, the points of inflection of the standards and of multimodale distributions composed of narrow (Poisson like) peaks in microemulsion were examined. When conferred with the theoretical values which were calculated for assumed Poisson distributions the respective deviations from the "true" ones were as high as 10% (almost reaching 20% in unfavorable cases). Simple (correction) procedures were tested in order to obtain the actual average values as well as the effective points of inflection of narrow distributions.

A graphical method for understanding the kinetics of peak capacity production in gradient elution liquid chromatography

A novel graphical method for assessing the compromise between conditional peak capacity and separation speed for packed bed columns under gradient conditions has been developed and applied to the separation of peptides. This approach is analogous to and complements the conventional "Poppe plot" used to study plate count in isocratic separations. The use of the new plot can assist the design of appropriate column formats (e.g. particle size and column length) for both dimensions in gradient elution two-dimensional liquid chromatography (2DLC). Particularly for the second dimension of 2DLC, we find that smaller particles provide faster separations even though fast separations based on particles smaller than 2 microm are practically limited by the required miniscule column length. We also find that high temperatures strongly enhance the kinetics of peak capacity production whereas higher pressures help achieve larger absolute peak capacities albeit at the cost of longer analysis time.

Characterization of polydisperse poly(vinyl chloride) by temperature gradient interaction chromatography

Temperature gradient interaction chromatography (TGIC) was employed to fractionate a commodity polymer, poly(vinyl chloride) (PVC) with wide molecular weight distribution (MWD). The TGIC fractionation was carried out with C18 bonded silica and dimethylformamide (DMF) as the stationary and mobile phase, respectively. TGIC exhibited a high resolution to fractionate the PVC into the fractions with a narrow MWD comparable to the anionically polymerized standards. In combination with light scattering detection, TGIC is able to characterize the polymers with wide MWD and shows a good potential to be further developed as a new preparative fractionation method of synthetic polymers.

Fluorescence-detection size-exclusion chromatography for precrystallization screening of integral membrane proteins

Formation of well-ordered crystals of membrane proteins is a bottleneck for structure determination by X-ray crystallography. Nevertheless, one can increase the probability of successful crystallization by precrystallization screening, a process by which one analyzes the monodispersity and stability of the protein-detergent complex. Traditionally, this has required microgram to milligram quantities of purified protein and a concomitant investment of time and resources. Here, we describe a rapid and efficient precrystallization screening strategy in which the target protein is covalently fused to green fluorescent protein (GFP) and the resulting unpurified protein is analyzed by fluorescence-detection size-exclusion chromatography (FSEC). This strategy requires only nanogram quantities of unpurified protein and allows one to evaluate localization and expression level, the degree of monodispersity, and the approximate molecular mass. We show the application of this precrystallization screening to four membrane proteins derived from prokaryotic or eukaryotic organisms.

A protocol for designing comprehensive two-dimensional liquid chromatography separation systems

In this paper a protocol is proposed for establishing suitable column dimensions (length and diameters), particle sizes, flow rates, and second-dimension injection volumes (i.e. loop sizes) in comprehensive two-dimensional liquid chromatography (LC x LC). The chromatographer should select the maximum allowable first-dimension retention time, which is approximately equal to the overall analysis time. Also, (s)he should define the maximum allowable pressure in both dimensions and the (minimum) diameter of the first-dimension column. The proposed protocol provides design parameters corresponding to the ideal (theoretically optimal) conditions or to realistic practical conditions. The protocol also allowed us to study the implications of contemporary developments in LC, such as the use of high temperatures (implying reduced viscosities and increased diffusion coefficients), monolithic columns (implying smaller flow-resistance factors), and ultra-high-pressure LC. The combination of (reversed-phase or normal-phase) liquid chromatography with size-exclusion chromatography (LC x SEC) is frequently employed for analysing complex polymers. The proposed protocol is used to design a suitable LC x SEC system under realistic conditions. The results resemble the systems that have been designed and implemented by expert chromatographers, but they also indicate how current practice can be improved.

Alternative approaches for the estimation of the band broadening parameters in single-detection size exclusion chromatography

New approaches for the determination of the extent of symmetric and asymmetric band broadening (BB) in size exclusion chromatography (SEC) are presented. For this purpose raw data was simulated by starting with either a theoretical Poisson number chain length distribution (NCLD), or a log-normal weight chain length distribution (WCLD). Each distribution was first converted to a BB-free mass chromatogram, as typically obtained from a standard differential refractive index detector. Then, the broadened (or "measured") chromatograms were simulated by convoluting the BB-free chromatograms with a BB function, which was assumed to follow symmetrical (Gauss) as well as unsymmetrical (exponentially modified Gauss) function. A broad range of BB parameters (standard deviation, sigma(BB), and exponential decay, tau(BB)) was used for the simulations. The approaches are based on the determination of the points of inflection belonging to the peak of the broadened chromatogram, and closed as well as empirically derived equations connecting the peak width, its variance, and the parameters sigma(BB) and tau(BB). The developed methods are applicable for Poisson distributions well above a peak chain length of 100.

Fast size-exclusion chromatography--theoretical and practical considerations

Fast SEC is a very interesting modification of conventional SEC. The need for it emerges from combinatorial chemistry and high-throughput experimentation, where high-speed analyses are required. The different approaches to change the speed of analysis are extensively described in this paper. Special attention is paid to the trade-off between analysis time and resolution and to the selection of optimal column lengths and flow rates. Simulations are used to design and to understand experiments. Integrity plots are constructed to judge the quality of various SEC systems. Fast separations in size-exclusion chromatography are found to be more favorable than suggested by conventional theory. The results are based on experimental data obtained for polystyrene using THF as mobile phase.

Comprehensive two-dimensional liquid chromatography for the characterization of functional acrylate polymers

Comprehensive two-dimensional liquid chromatography-size-exclusion chromatography (LC x SEC) was investigated as a tool for the characterization of functional poly(methyl methacrylate) (PMMA) polymers. Ultraviolet-absorbance and evaporative light-scattering detection (ELSD) were used. A simple method to quantify ELSD data is presented. Each data point from the ELSD chromatogram can be converted into a mass concentration using experimental calibration curves. The qualitative and quantitative information obtained on two representative samples is used to demonstrate the applicability of LC x SEC for determining the mutually dependent molar-mass distributions (MMD) and functionality-type distributions (FTD) of functional polymers. The influence of the molar mass on the retention behavior in LC was investigated using LC x SEC for hydroxyl-functional PMMA polymers. The critical conditions, at which retention is--by definition--independent of molar mass, were not exactly the same for PMMA series with different end-groups. Our observations are in close agreement with theoretical curves reported in the literature. However, for practical applications of LC x SEC it is not strictly necessary to work at the exact critical solvent composition. Near-critical conditions are often sufficient to determine the mutually dependent distributions (MMD and FTD) of functional polymers.