Computer simulation of particle separation based on non-equilibrium swelling

Steric/hyperlayer field-flow fractionation (FFF) is an established analytical technique for separating and characterizing particles in the 1-100 microns diameter range. The separation can be based on differences in size, density, shape and mechanical properties of the particles. In the course of an analysis of the water transporter system of Chinese hamster ovary (CHO) cells and one of their high permeability mutants, the first successful attempt was made to use the steric/hyperlayer FFF system for the purpose of separating particles based on a time-dependent property, namely, the differential swelling of the two cell types. The present study was undertaken to simulate numerically the separation and suggest selection of operating conditions to minimize repetitive experiments. The computer simulation was developed using Maple V, a symbolic computing environment. It is shown that the model is able to predict an optimal velocity of carrier buffer that maximizes resolution. Predicted velocity/resolution pairs are in good agreement with available experimental data. Empirical models for the lift forces encountered in such FFF experiments, and for the zone broadening observed in work with cell sized particles, form the basis for this model.     

无固定相分离-电感耦合等离子体质谱法在环境中痕量金属纳米颗粒分析中的应用

环境中金属纳米颗粒的分析检测不仅需要关注其浓度和化学组成,还需要对其形状、粒径和表面电荷等进行表征。此外,环境中金属纳米颗粒的分析需要解决其低赋存浓度以及复杂基质干扰的难题。无固定相分离技术与电感耦合等离子体质谱(ICP-MS)的在线联用,具有较强的颗粒分离能力和较低的元素检出限,能够快速准确地提供金属纳米颗粒的粒径分布、化学组成等信息,在金属纳米颗粒的分离检测方面表现出极大的潜能。但这一联用技术尚无法获得金属纳米颗粒物的颗粒数浓度和单个颗粒的元素信息,难以判断金属纳米颗粒涂层厚度、纯度以及颗粒的均相/异相团聚行为等。新兴的单颗粒-电感耦合等离子体质谱(SP-ICP-MS)与无固定相分离技术的在线联用,可以获得金属纳米颗粒的流体动力学粒径、元素质量计算粒径和颗粒数浓度等信息,进而弥补无固定相分离与ICP-MS在线联用技术的不足。该文介绍了流体动力色谱、毛细管电泳和场流分离3种常用无固定相分离技术的分离机制和适用检测器,着重综述了无固定相分离技术与ICP-MS/SP-ICP-MS在线联用技术的特点及其在环境金属纳米颗粒分析中的应用。关于场流分离,主要介绍了可以与ICP-MS联用的沉降场流分离和流场流分离。该文还对流体动力色谱、毛细管电泳和流场流分离与ICP-MS在线联用技术的特点进行了比较。最后,该文对无固定相分离技术与ICP-MS/SP-ICP-MS在线联用技术的发展提出了展望。     

Separation of Water‐in‐Oil Emulsions Using Glass Fiber Media Augmented with Polymer Nanofibers

Water‐in‐oil emulsion separations are important to the petrochemical industry for product quality, safety, environmental, and economic reasons. Glass fiber filter media are often used to remove water droplets out of water‐in‐oil emulsions. The experimental results in this work show that 1% by mass of polyamide nanofibers with diameters of about 150 nm added to conventional micron‐sized glass fiber filter media improves the separation efficiency of the filter media from 71 to 84%. The addition of similar amounts of micron‐sized polyamide fibers to the glass fiber media do not improve filter capture efficiency.     

Asymmetrical flow field-flow fractionation technique for separation and characterization of biopolymers and bioparticles

Field-flow fractionation (FFF) is one of the most versatile separation techniques in the field of analytical separation sciences, capable of separating macromolecules in the range 10³–10¹⁵ g mol⁻¹ and/or particles with 1 nm–100 μm in diameter. The most universal and most frequently used FFF technique, flow FFF, includes three types of techniques, namely symmetrical flow FFF, hollow fiber flow FFF, and asymmetrical flow FFF which is most established variant among them. This review provides a brief look at the theoretical background of analyte retention and separation efficiency in FFF, followed by a comprehensive overview of the current status of asymmetrical flow FFF with selected applications in the field of biopolymers and bioparticles.     

Field-flow fractionation of proteins, polysaccharides, synthetic polymers, and supramolecular assemblies

This review summarizes developments and applications of flow and thermal field-flow fractionation (FFF) in the areas of macromolecules and supramolecular assemblies. In the past 10 years, the use of these FFF techniques has extended beyond determining diffusion coefficients, hydrodynamic diameters, and molecular weights of standards. Complex samples as diverse as polysaccharides, prion particles, and block copolymers have been characterized and processes such as aggregation, stability, and infectivity have been monitored. The open channel design used in FFF makes it a gentle separation technique for high- and ultrahigh-molecular weight macromolecules, aggregates, and self-assembled complexes. Coupling FFF with other techniques such as multiangle light scattering and MS provides additional invaluable information about conformation, branching, and identity.     

Osmolarity effects on red blood cell elution in sedimentation field-flow fractionation.

Field-flow fractionation (FFF) is an analytical technique particularly suitable for the separation, isolation, and characterization of macromolecules and micrometer- or submicrometer-sized particles. This chromatographic-like methodology can modulate the retention of micron-sized species according to an elution mode described to date as "steric hyperlayer". In such a model, differences in sample species size, density, or other physical parameters make particle selective elution possible depending on the configuration and the operating conditions of the FFF system. Elution characteristics of micron-sized particles of biological origin, such as cells, can be modified using media and carrier phases of different osmolarities. In these media, a cells average size, density, and shape are modified. Therefore, systematic studies of a single reference cell population, red blood cells (RBCs), are performed with 2 sedimentation FFF systems using either gravity (GrFFF) or a centrifugational field (SdFFF). However, in all cases, normal erythrocyte in isotonic suspension elutes as a single peak when fractionated in these systems. With carrier phases of different osmolarities, FFF elution characteristics of RBCs are modified. Retention modifications are qualitatively consistent with the "steric-hyperlayer" model. Such systematic studies confirm the key role of size, density, and shape in the elution mode of RBCs in sedimentation FFF for living, micronsized biological species. Using polymers as an analogy, the RBC population is described as highly "polydisperse". However, this definition must be reconsidered depending on the parameters under concern, leading to a matricial concept: multipolydispersity. It is observed that multipolydispersity modifications of a given RBC population are qualitatively correlated to the eluted sample band width.     

Field-flow fractionation: Analytical and micropreparative methodology

Since the introduction of the general concept, field-flow fractionation (FFF) was developed to a complex of separation methods that differ by the fundamental processes underlying and accompanying the separation. In this review, the basic principles on which this separation methodology lies are presented, the most important methods and techniques applicable for analytical and preparative fractionations are described, the first approximation theoretical treatment of the separation processes is outlined, and typical applications for analytical and micropreparative purposes are demonstrated. The main goal is to show that FFF represents an interesting and competitive option of the separation methods applicable in analytical chemistry. The existence of some conflicting opinions concerning the theory as well as the experiments does not prohibit the analytical and preparative use of FFF. If not regarded only as a routine analytical tool, it should stimulate the research and development efforts. On the other hand, when used as an analytical tool, even if the approximate theoretical models are not fully supported by the experiments, the correct analytical result can be obtained from FFF (as well as from any other analytical separation method) by using a calibration procedure and an appropriate treatment and interpretation of the raw experimental data.     

Different elution modes and field programming in gravitational field-flow fractionation. IV. Field programming achieved with channels of non-constant cross-sections

Force field programming provided increased speed of separation with an improved resolution and detection capability in many field-flow fractionation (FFF) techniques. Gravitational field-flow fractionation (GFFF) uses the Earth's gravitational field to cause the settlement of particles towards the channel accumulation wall. Although this field is constant and relatively weak, there are different ways to implement force field programming in GFFF. Because hydrodynamic lift forces (HLF) participate in the separation process in focusing (hyperlayer) elution mode, they can control the resulting force field acting on particles via changes in flow-velocity. These changes can be accomplished by a programmable pump or with channels of non-constant cross-sections. This work is focused on flow-velocity programming accomplished with channels of non-constant cross-sections. Three trapezoidal channels of decreasing breadth and two channels of decreasing height (along the longitudinal axis) are tested as tools for optimization of the separation of a model silica gel particle mixture. The trapezoidal channels yielded reduced separation times. However, taking into account both speed of separation and resolution, the optimization effect was lower compared with the flow-rate gradients generated by a programmable pump. The channels of non-constant height did not yield advantageous separations.     

Low-capacity channel designed for particle separation with controlled electric fields and evaluation of involved forces

Electric field is one of the suitable physical fields applicable to particle separations. Although long rectangular channel is used for particle separation in usual electrical field flow fractionation (FFF), a short low-capacity channel can replace it if the field is precisely controlled. Several separation principles are proposed with this channel. The elution behavior of particles has revealed that the gravitational, diffusion, and hydrodynamic lift force (HLF) play important roles in the determination of the elution behavior of particles. The elution threshold voltage (V(th)) was defined and experimentally determined for various system configurations and particles. The electric force no longer overcomes the other forces, and particles are taken off the wall, when the applied voltage becomes lower than V(th). V(th) values have allowed us not only to estimate surface charge density of a particle but also to evaluate the hydrodynamic lift force against particle.     

Trends in Polymer and Particle Characterization by Microfluidic Field-Flow Fractionation Methods: Science or Business?

More than 45 years have passed since the invention of field-flow fractionation (FFF). During this time, several methods and techniques, differing mainly by the nature of the applied field, have been proposed and experimentally implemented. However, only few of them are currently in practical laboratory use. Recent trends of miniaturization of all separation techniques have also been followed in the development of FFF apparatus. The aim of this work is to give an overview of the advances that are important in the practical use of microfluidic FFF techniques. Another aim is a critical evaluation of the crucial characteristics of the most widespread FFF techniques performed in standard-size channels.     

Methods for continuous flow fractionation of microparticles: Outlooks and fields of application

The development of new methods for fractionating particles of a different nature is becoming more important in solving some scientific and technological problems. This paper presents a brief review in the theory and practice of the most common techniques for microparticle fractionation (0.1–100 μm). These are dry and wet sieving, elutriation, sequential filtration, split-flow thin fractionation (SPLITT system), field-flow fractionation (FFF), membrane filtration, and capillary electrophoresis. Special attention is paid to the FFF technique, which offers a unique potential for the separation of different materials, from biopolymers and microorganisms to colloidal and solid particles, and the estimation of their physical properties. An alternative version of sedimentation FFF is described, namely, the fractionation of microparticles in rotating coiled columns. The main advantages and limitations of the methods are revealed and their outlooks and fields of applications are envisaged.     

Photopolymerized sol–gel monoliths for separations of glycosylated proteins and peptides in microfluidic chips

Photopolymerized silica sol–gel monoliths, functionalized with boronic acid ligands, have been developed for protein and peptide separations in polydimethylsiloxane microfluidic devices. Pore size characterization of the monoliths was carried out with SEM, image analysis, and differential scanning calorimetry to evaluate both the micron‐sized macropores and the nanometer‐sized mesopores. Monoliths were functionalized with boronic acid using three different immobilization techniques. Batch experiments were conducted to determine the capacity of the monoliths and selectivity toward cis‐diol‐containing compounds. Conalbumin was used as a model glycoprotein, and a tryptic digest of the glycoprotein horseradish peroxidase was used as a peptide mixture to demonstrate proof‐of‐concept extraction of glycoproteins and glycopeptides by the monoliths formulated in polydimethylsiloxane microfluidic chips. For proteins, fluorescence detection was used, whereas the peptide separations employed off‐line analysis using MALDI‐MS.     

Analytical methods for separating and isolating magnetic nanoparticles

Despite the large body of literature describing the synthesis of magnetic nanoparticles, few analytical tools are commonly used for their purification and analysis. Due to their unique physical and chemical properties, magnetic nanoparticles are appealing candidates for biomedical applications and analytical separations. Yet in the absence of methods for assessing and assuring their purity, the ultimate use of magnetic particles and heterostructures is likely to be limited. In this review, we summarize the separation techniques that have been initially used for this purpose. For magnetic nanoparticles, it is the use of an applied magnetic flux or field gradient that enables separations. Flow based techniques are combined with applied magnetic fields to give methods such as magnetic field flow fractionation and high gradient magnetic separation. Additional techniques have been explored for manipulating particles in microfluidic channels and in mesoporous membranes. Further development of these and new analytical tools for separation and analysis of colloidal particles is critically important to enable the practical use of these, particularly for medicinal purposes.     

Cellular separations: a review of new challenges in analytical chemistry

The ability to generate a sample of cells of a given phenotype is a prerequisite for many cellular assays. In response to this growing need, numerous methods for cell separation have been developed in recent years. This Review covers recent progress in the field of cell separations and cell chromatography. Cell separation principles—such as size and affinity capture—are discussed, as well as conventional methods such as fluorescence-activated cell sorting and magnetic sorting. Planar flow cell arrays, dielectrophoresis, field-flow methods, and column separation devices are reviewed, as well as applications of these methods to medicine and biotechnology. Cell attachment and adhesion strategies and a comparison of techniques are also presented.     

Separation of carbon nanotubes by frit inlet asymmetrical flow field-flow fractionation

Flow field-flow fractionation (flow FFF), a separation technique for particles and macromolecules, has been used to separate carbon nanotubes (CNT). The carbon nanotube ropes that were purified from a raw carbon nanotube mixture by acidic reflux followed by cross-flow filtration using a hollow fiber module were cut into shorter lengths by sonication under a concentrated acid mixture. The cut carbon nanotubes were separated by using a modified flow FFF channel system, frit inlet asymmetrical flow FFF (FI AFIFFF) channel, which was useful in the continuous flow operation during injection and separation. Carbon nanotubes, before and after the cutting process, were clearly distinguished by their retention profiles. The narrow volume fractions of CNT collected during flow FFF runs were confirmed by field emission scanning electron microscopy and Raman spectroscopy. Experimentally, it was found that retention of carbon nanotubes in flow FFF was dependent on the use of surfactant for CNT dispersion and for the carrier solution in flow FFF. In this work, the use of flow FFF for the size differentiation of carbon nanotubes in the process of preparation or purification was demonstrated.     

Liquid Crystal Emulsions

We review recent findings about the behavior of emulsions made of droplets suspended in liquid crystalline materials. By contrast to classical emulsions, which are usually made of isotropic oils and water, liquid crystal emulsions exhibit a variety of structures result in the ordering of the continuous phase. The droplets induce the formation of topological defects and distortions that lead to strong and anisotropic elastic forces between the particles. These elastic forces govern the stability and the ordering of the particles. This is observed in aqueous emulsions as well as in non-aqueous emulsions obtained from phase separation phenomena. It is shown that phase separations in liquid crystals can lead to the formation of highly ordered arrays of uniformly sized droplets. More generally, ordered structures seen in liquid crystal emulsions are of interest as examples of topologicallv-controlled organizations; they are also of potential practical importance as a novel way to control both the stability and the structures of colloidal particles.     

Separation and characterization of nanoparticles in complex food and environmental samples by field-flow fractionation

The thorough analysis of natural nanoparticles (NPs) and engineered NPs involves the sequence of detection, identification, quantification and, if possible, detailed characterization. In a complex or heterogeneous sample, each step of this sequence is an individual challenge, and, given suitable sample preparation, field-flow fractionation (FFF) is one of the most promising techniques to achieve relevant characterization.The objective of this review is to present the current status of FFF as an analytical separation technique for the study of NPs in complex food and environmental samples. FFF has been applied for separation of various types of NP (e.g., organic macromolecules, and carbonaceous or inorganic NPs) in different types of media (e.g., natural waters, soil extracts or food samples).FFF can be coupled to different types of detectors that offer additional information and specificity, and the determination of size-dependent properties typically inaccessible to other techniques. The separation conditions need to be carefully adapted to account for specific particle properties, so quantitative analysis of heterogeneous or complex samples is difficult as soon as matrix constituents in the samples require contradictory separation conditions. The potential of FFF analysis should always be evaluated bearing in mind the impact of the necessary sample preparation, the information that can be retrieved from the chosen detection systems and the influence of the chosen separation conditions on all types of NP in the sample. A holistic methodological approach is preferable to a technique-focused one.     

Sonication effect on cellular material in sedimentation and gravitational field flow fractionation

Sonication procedures are generally used prior to field flow fractionation (FFF) separation in order to produce suspensions without aggregates. Yeast cells manufactured in active dry wine yeast (ADWY) were placed in an ultrasound water bath in order to disrupt possible clumps and to obtain a single-cell suspension to be used in optimal conditions during fermentation processes. In order to determine whether this sample preparation procedure meets absolute needs, different yeast samples before and after sonication were analysed by two field flow fractionation techniques. It is shown that 2 min of sonication in the sample preparation process is sufficient to obtain an optimal dispersion of the yeast cells, that is, without critical percentage of aggregates. To demonstrate this effect, photographs of the yeast cell suspensions were performed with non-sonicated and sonicated yeast sample dispersion. The resulting data are compared with the elution profiles obtained from the two different FFF techniques. It is demonstrated that fractogram profiles prove the effectiveness of sonication methodologies.