Fractionation of Humic Substances by Asymmetrical Flow Field-Flow Fractionation

Asymmetrical flow field-flow fractionation was used to investigate the effects of pH and ionic strength of the buffer, and the binding of polyaromatic hydrocarbons (PAHs) on the particle sizes of humic substances (HSs). Particle sizes were greater when HSs were present in acidic medium with phosphate buffer than when they were present in alkaline medium or in acidic medium with acetate buffer. The association of PAH did not lead to increase sizes of HSs. Bivalent calcium ion had a greater effect on the size than did monovalent sodium ion. Particle sizes in river water and seawater were mostly of the same magnitude of the standards HSs. Some larger particles (30–70 nm) were also found.Dedicated to Professor K. Jinno on the occasion of his 60^th birthday     

Separation and Dispersion in Sedimentation Field-Flow Fractionation

Abstract

Contributions of separation and dispersion to the total zone width of a polydisperse latex sample under various flow rates and retentions were studied. Both the direct flow and the reverse flow techniques were employed and the experimental results were compared with theoretical relationships. The results showed a good agreement between the theory and the experiment under different conditions. A good agreement between the mean particle diameters calculated from our experimental data and those given by the producer was found. The width of the particle size distribution characterized by the standard deviation was found about two fold higher than that given by the producer.     

Fractionation and Size Distribution of Water Soluble Polymers by Flow Field-Flow Fractionation

Abstract

Flow field-flow fractionation (flow FFF) is introduced as a chromatographic-like method with a potential for separating and characterizing water soluble polymers. The theory of the method is summarized, showing that one gets a size distribution curve based on the Stokes diameter, d. Problems in interpreting the elution profile in both flow FFF and gel permeation chromatography are discussed in the light of complications arising from electrostatic chain expansion in polyelectrolytes.

The experimental approach is described using a channel of 2.00 ml volume. Sulfonated polystyrenes of three different molecular weights are separated from one another with and without added salts. The dependence of retention on sample size is shown to be least in the salt solution, indicating that this is most suitable for analytical work.

The sodium salts of polyacrylic acid are also investigated. Distinct elution profiles are noted for two of these polydisperse polymers. Size distribution curves for the 2,000,000 MW sample curves are obtained from, the elution profiles and are shown to be independent of experimental variations. Finally, fractions are collected after separation and rerun through the coloumn, showing a reasonable confirmation of the expected fractionation effect.     

Thermal Field-Flow Fractionation as a Powerful Tool for the Fractionation of Complex Synthetic Polymers: A Perspective

Chromatographia - Synthetic polymers have complex molecular structures with distributions in molar mass, chemical composition, functionality and molecular topology. For the comprehensive analysis...     

Nonequilibrium and Polydispersity Peak Broadening in Thermal Field-Flow Fractionation

Abstract

New theoretical procedures and an expanded data base have been combined to yield improved calculations for nonequilibrium plate height and polydispersity contributions in field-flow fractionation (FFF). Five thermal FFF column systems having a fourfold range in column width and length were operated with four solutes to yield eleven distinct channel-solute systems. After data were corrected for relaxation effects, comparison of experimental plate height measurements with theory showed good overall agreement for nonequilibrium parameter X. Calculated values of polydispersity agreed reasonably well with supplier's values. Data reliability has been discussed in relationship to column dimensions and experimental parameters.     

Correction to: Thermal Field-Flow Fractionation as a Powerful Tool for the Fractionation of Complex Synthetic Polymers: A Perspective

Chromatographia - A correction to this paper has been published: https://doi.org/10.1007/s10337-021-04055-6     

Asymmetric Flow Field-Flow Fractionation: Current Status,Possibilities, Analytical Limitations and Future Trends

Chromatographia - The development and applications of asymmetric flow field-flow fractionation (AF4) are outlined in comparison with the older and better-known size exclusion chromatography. Recent...     

Impact of Ionic Strength of Carrier Liquid on Recovery in Flow Field-Flow Fractionation

Asymmetrical flow field-flow fractionation (AF4) and hollow-fiber flow field-flow fractionation (HF5) are techniques widely used in analytical, industrial and biological analyses. The main problem in all AF4 and HF5 analyses is sample loss due to analyte–membrane interactions. In this work the impact of liquid carrier composition on latex nanoparticles (NPs) separation in water and two different concentrations of NH₄NO₃ was studied. In AF4, a constant trend of decreasing the size of 60 and 121.9 nm particles induced by the ionic strength of the carrier liquid has been observed. In contrast, an agglomeration effect of the biggest 356 nm particles was observed when increasing ionic strength, which induced a significant drop of recovery to 35%. H5F provides better resolution and intensified peaks of NPs, but careful optimisation of system parameters is mandatory to obtain good separation.     

Role of the shape of various bacteria in their separation by Microthermal Field-Flow Fractionation

The steady-state movement of the spherical and non-spherical particles, such as prolate or oblate rotational ellipsoids, cylinders, or parallelepipeds, suspended in a liquid and exposed to a unidirectional temperature gradient, is analyzed theoretically. The differences in the ratios of the rotational to translational diffusion coefficients of the non-spherical to spherical particles, the heterogeneity of thermal conductivity of the particle body, and the heterogeneity in surface chemical nature make possible to separate the particles according to differences in shape. Preliminary experimental separations of Gram-positive and Gram-negative, nearly spherical and rod-shaped bacteria performed by Microthermal Field-Flow Fractionation confirmed that the fractionation of the cells according to differences in shape is possible.     

Correction to: Asymmetric Flow Field-Flow Fractionation: Current Status,Possibilities, Analytical Limitations and Future Trends

Chromatographia - A correction to this paper has been published: https://doi.org/10.1007/s10337-021-04054-7     

Measurement Bias on Nanoparticle Size Characterization by Asymmetric Flow Field-Flow Fractionation Using Dynamic Light-Scattering Detection

In this work, we highlight the influence of the particle–particle interaction on the retention behavior in asymmetric flow field-flow fractionation (A4F) and the misunderstanding considering the size determination by a light-scattering detector (static and dynamic light scattering) by comparing fullerene nanoparticles to similar sized polystyrene nanoparticle standards. The phenomena described here suggest that there are biases in the hydrodynamic size and diffusion determination induced by particle–particle interactions, as characterized by their virial coefficient. The dual objectives of this paper are to (1) demonstrate the uncertainties resulting from the current practice of size determination by detectors coupled to an A4F system and (2) initiate a discussion of the effects of particle–particle interactions using fullerene nanoparticles on their characterization as well as their origins. The results presented here clearly illustrate that the simple diffusion coefficient equation that is generally used to calculate the hydrodynamic size of nanoparticles (NPs) cannot be considered for whole fractograms according to their size distribution. We tried to identify particle interactions that appear during fractionation and demonstrated using the fully developed diffusion coefficient equation. We postulate that the observed interaction-dependent retention behavior may be attributed to differences in the virial coefficient between NPs and between NPs and the accumulation wall (membrane surface) without quantifying it. We hope that our results will stimulate discussion and a reassessment of the size determination procedure by A4F-LS to more fully account for all the influential material parameters that are relevant to the fractionation of nanoscale particles by A4F.     

Sedimentation-Flotation Focusing Field-Flow Fractionation in Channels with Modulated Cross-Sectional Permeability. I. Theoretical Analysis

Abstract

A new-shaped cross-section of a channel with modulated permeability used in Sedimentation-Flotation Focusing Field-Flow Fractionation is proposed. The shape of the resulting velocity profile inside the channel is described as a function of the geometric channel characteristics. Basic separation parameters such as retention, efficiency and the related resolution are discussed. The principle of a channel with modulated permeability can also be applied to other subtechniques of Field-Flow Fractionation.     

Three-Dimensional Isoviscous Flow Velocity Profiles and Resolution in Channels with Modulated Cross-Sectional Permeability for Focusing Field-Flow Fractionation

Abstract

The form of the flow velocity profile developed in a carrier liquid flowing in separation channel for focusing field-flow fractionation can be controlled by manipulating the shape of the channel cross-section. The velocity profiles established in modulated cross-sectional permeability channels under the conditions of isoviscous flow were described previously by using the approximate solution of Navier-Stokes equation. In this paper, the previous approach is compared with an exact solution. The theoretical resolution is calculated for the actual trapezoidal cross-section channels and compared with the experimentally achieved resolutions. A fair agreement between the calculated and experimental resolutions was obtained.     

Influence of carrier solution ionic strength and injected sample load on retention and recovery of natural nanoparticles using Flow Field-Flow Fractionation

Natural nanoparticles, including both natural organic matter (NOM) and inorganic mineral-like phases, have been broadly characterized using Flow Field-Flow Fractionation (FlowFFF). Calibration with polystyrene sulfonate (PSS) standards was generally carried out in order to determine the molecular weight distribution of the NOM, however if the analyzed sample has a different charge density compared to the PSS standards, the resulting molecular weight distribution may become meaningless. The presented study therefore investigates and compares the influences of ionic strength and sample load on the retention time and recovery of both PSS standards and natural nanoparticles from a variety of sources. The minimum ionic strength in the carrier solution and the maximum injected sample load required for satisfactory separation depend on the molecular weight of the PSS standards and on the nature of the NOM. The degree to which results depend on conditions and parameters within the FlowFFF varies significantly between the different natural nanoparticle samples. We found that it may be necessary to calibrate the channel under different conditions from the actual sample runs. Under well controlled and documented conditions this could represent an important move away from the paradigm of "same conditions for standards and sample". From all conditions tested, the most reliable molecular weight calibrations were obtained at elevated ionic strengths in the carrier solution (>0.04 M) and low injected mass of PSS. However, even under these optimized conditions variations of up to 20% occur in the calculated molecular weights, and the recovery of NOM falls by up to 50% at high ionic strengths. Many applications aim for both correct molecular weight distribution and the measurement of low concentrations of elements bound to natural nanoparticles. We conclude, however, that finding conditions that are equally optimal for both of these analytical tasks is not always feasible.     

Tutorial: Capillary Electrophoresis

In recent years a number of exciting developments have emerged in the area of scientific computational tools for classroom use. Computer Algebra Systems (CASs), for example, Maple, are at the forefront of this arena. Such tools have been long sought by teachers of physical chemistry, inherently a mathematics intensive subject. With a CAS at hand, students can look forward to taking college science courses, like physical chemistry, without the usual mathematics anxiety. These tools can be used to do numerical and symbolic mathematics including calculus and linear algebra. In addition, they have wonderful graphics capabilities that include three-dimensional plots, contour plots, and animations. This paper describes the implementation of Maple in two junior-level physical chemistry courses. The materials used for beginning workshops are presented here and additional examples of Maples graphic and algebraic capabilities are described.     

Pre-apoptotic sub-population cell sorting from diosgenin apoptosis induced 1547 cells by Sedimentation Field-Flow Fractionation. The effect of channel thickness on sorting performance

Apoptosis is one of the most important phenomena in cell biology. Pre-apoptotic cells, defined as cells engaged in early stages of apoptosis, could be used as a cellular tool to study apoptosis pathways. The human 1547 osteosarcoma cell line and diosgenin (a plant steroid) association was selected as an in vitro cellular apoptosis model. In a previous study, using this model, we demonstrated that SdFFF monitored apoptosis induction as early as 6h after incubation. In this study, we investigated the capacity of Sedimentation Field-Flow Fractionation (SdFFF) to sort an enriched population of pre-apoptotic cells from 1547 cells incubated for 6 h with 40 microM diosgenin. In that way, two different separation devices which differed especially in channel thickness, 125 and 175 microm, were used and compared. Results showed, for the first time, that SdFFF is an effective method to obtain an enriched pre-apoptotic sub-population. These results suggest, as a new application, that SdFFF could be an included tool in the study of apoptotic mechanisms or the kinetic action of apoptotic drugs.     

Application of a high-performance liquid chromatography fluorescence detector as a nephelometric turbidity detector following Field-Flow Fractionation to analyse size distributions of environmental colloids

A new operation mode for HPLC-type fluorescence detectors is presented and evaluated using synthetic and environmental particles in the colloidal size range. By applying identical wavelengths for excitation and emission a nephelometric turbidity or single angle light scattering detector is created which can be easily coupled to flow or sedimentation Field-Flow Fractionation (Flow FFF or Sed FFF) for the analysis of colloidal dispersions. The results are compared with standard UV-vis detection methods. Signals obtained are given as a function of particle size and selected detection wavelength. Conclusions can be drawn which affect the current practice of FFF but also for other techniques as groundwater sampling and laboratory column experiments when turbidity is measured in nephelometric mode and in small sample volumes or at low flow rates.