Field-flow Fractionation Analysis Research Articles

Implications of Free and Occluded Fine Colloids for Organic Matter Preservation in Arable Soils.

Colloidal organo-mineral associations contribute to soil organic matter (OM) preservation and mainly occur in two forms: (i) as water-dispersible colloids that are potentially mobile (free colloids) and (ii) as building units of soil microaggregates that are occluded inside them (occluded colloids). However, the way in which these two colloidal forms differ in terms of textural characteristics and chemical composition, together with the nature of their associated OM, remains unknown. To fill these knowledge gaps, free and occluded fine colloids <220 nm were isolated from arable soils with comparable organic carbon (Corg) but different clay contents. Free colloids were dispersed in water suspensions during wet-sieving, while occluded colloids were released from water-stable aggregates by sonication. The asymmetric flow field-flow fractionation analysis on the free and occluded colloids suggested that most of the 0.6-220 nm fine colloidal Corg was present in size fractions that showed high abundances of Si, Al, and Fe. The pyrolysis-field ionization mass spectrometry revealed that the free colloids were relatively rich in less decomposed plant-derived OM (i.e., lipids, suberin, and free fatty acids), whereas the occluded colloids generally contained more decomposed and microbial-derived OM (i.e., carbohydrates and amides). In addition, a higher thermal stability of OM in occluded colloids pointed to a higher resistance to further degradation and mineralization of OM in occluded colloids than that in free colloids. This study provides new insights into the characteristics of subsized fractions of fine colloidal organo-mineral associations in soils and explores the impacts of free versus occluded colloidal forms on the composition and stability of colloid-associated OM.

The concentration and size distribution of iron‐rich colloids in pore waters are related to soil organic matter content and pore water calcium concentration

AbstractIron (Fe)‐rich colloids in the environment have a high surface reactivity and facilitate transport of oxyanions and trace metal cations in soil. This study was set up to help identify the soil properties that might affect the concentrations of colloidal Fe and its size distribution in pore waters of soils. The pore water was isolated by centrifugation from a collection of 97 topsoils with contrasting properties and land use. The total Fe concentration in the pore waters ranged between 0.2 and 26 μM (10th–90th percentile) and was largest at low soil solution calcium (Ca) and high dissolved organic carbon (DOC), indicating that enhanced colloidal stability determines total Fe in solution. The colloidal size distribution (&lt;100 nm) of Fe in the pore waters of 11 soils was determined with flow field flow fractionation (FlFFF‐UV‐ICP‐MS), which yielded three different fractions that varied strikingly among soils. The smallest fraction (&lt;5 nm) of Fe co‐eluted with high DOC and copper (Cu), suggesting mononuclear Fe‐organic carbon (OC) complexes. This fraction increased with an increasing DOC/Fe ratio in pore waters. The 5–50‐nm fraction of Fe prevailed in soils with &gt;3.5% organic carbon (%OC), whereas the 50–100‐nm fraction was dominant in soils with low %OC content. This suggests that natural organic matter inhibits crystallization and growth of mineral Fe particles. The elemental ratios of mineral colloids (&gt;5 nm) indicated the presence of clay minerals and Fe oxyhydroxides, which was confirmed by scanning electron microscopy (SEM) analysis. This study thus identified soil %OC and Ca in soil solution as the dominant factors predicting both the concentration and size of pore water Fe colloids, with the smallest and, potentially, most mobile Fe colloids occurring in OC‐rich soils.Highlights Pore water iron concentrations in topsoils are governed by colloid stability Flow field flow fractionation analysis allows characterization of iron colloids in the low nanometre range Iron colloid size and composition vary strikingly among soils Small iron colloids prevail in organic carbon‐rich soils due to colloid growth inhibition

Treatment of membrane concentrated leachate by two-stage electrochemical process enhanced by ultraviolet radiation: Performance and mechanism

Membrane systems are widely used for advanced leachate treatments in municipal waste incineration (MSWI) plants, resulting in the production of membrane concentrated leachate containing a high content of pollutants, especially refractory organics and salts. In this study, a two-stage electrochemical (TSE) process enhanced by ultraviolet (UV) radiation was applied to treat coagulated reverse osmosis concentrated leachate. Application of UV radiation throughout the TSE process produced remarkable results for pollutant removal because UV radiation promoted production of free radicals with strong oxidizing ability, which could function with active chlorine to oxidize pollutants, especially refractory organics. After the optimal UV-TSE (i.e., TSE process enhanced by UV radiation) treatment, the chemical oxygen demand, total organic carbon, light-absorbing substances (at 254 nm), ammonia nitrogen, and total nitrogen removal efficiencies were all more than 86%, and that of color, turbidity and chloride were more than 96%, which had better performance than TSE process. Following UV-TSE process, an obvious blue shift was observed in the UV–Vis spectra, with significant decrease in the absorbances in the UV region. The reduction in the intensity of peaks 1 and 2 in 3D fluorescence spectra was 87.37% and 88.90%, respectively. Flow field-flow fractionation analysis showed that the molecular weights of colored dissolved organic matter (DOM), humic-like DOM, and protein-like DOM deeply decreased. The UV-TSE treatment decomposed macromolecular organics into lower molecular organics more effectively and thoroughly, resulting in higher VOCs content in the treated sample, when compared with TSE-treated samples. These findings can shed light on the performance and organics removal mechanism of UV-TSE process, and provide a theoretical basis for the electrochemical treatment of membrane concentrated leachate from MSWI plants.

First Evidence of Acyl-Hydrolase/Lipase Activity From Human Probiotic Bacteria: Lactobacillus rhamnosus GG and Bifidobacterium longum NCC 2705.

Lactobacillus rhamnosus GG (ATCC 53103) and Bifidobacterium longum NCC 2705 are among the most studied probiotics. However, the first evidence of acyl hydrolase/lipase of two annotated proteins, one in each genome of these strains, is reported in this work. Signal peptide analysis has predicted that these proteins are exported to the extracellular medium. Both proteins were produced in Escherichia coli, purified and characterized. Molecular masses (without signal peptides) were 27 and 52.3 kDa for the proteins of L. rhamnosus and B. longum, respectively. Asymmetrical flow field-flow fractionation analysis has shown that both proteins are present as monomers in their native forms at pH 7. Both have shown enzymatic activity on pNP-laurate at pH 7 and 37°C. The enzyme from L. rhamnosus was characterized deeper, showing preference on pNP-esters with short chain fatty acids. In addition, a computational model of the 3D structure has allowed the prediction of the catalytic amino acids. The enzymatic activities using synthetic substrates were very low for both enzymes. The investigation of natural substrates and biological functions of these enzymes is still open.

Adsorption and molecular weight fractionation of dissolved organic matters with different origins on colloidal surface

Dissolved organic matter (DOM) adsorption on colloid surface occurred ubiquitously in aquatic ecosystems, while variations in molecular weight (MW) distribution during adsorption remained poorly understood. In this study, the adsorption and MW fractionation of aquatic DOMs with different origins (e.g., macrophyte- and algae-derived, MDOM and ADOM, respectively) on colloid surface were examined using total organic carbon, absorption and fluorescence spectroscopy, and flow field flow fractionation (FlFFF) analysis. Both the total organic carbon and spectroscopic results showed the predominant adsorption of DOMs within the first 45 min, which behaved not synchronously with MW fractionation. Quantitative FlFFF analysis further indicated that the organic ligands with different MWs exhibited different adsorption affinities on colloid surface. It was found that 5–15 kDa and 50 kDã0.45 μm were preferential adsorption fraction for humic- and protein-like MDOM, respectively, while 0.3–2 kDa and 0.3–50 kDa were preferential adsorption fraction for humic- and protein-like ADOM, respectively. Therefore, the MW fractionation of DOMs upon adsorption was highly dependent on DOM origins as well as specific components. Results obtained herein can enlarge our insights into adsorption and the resultant behavior and fate of DOMs that were highly related with the MW fractionation in aquatic environments.

Intriguing changes in molecular size and composition of dissolved organic matter induced by microbial degradation and self-assembly

Dissolved organic matter (DOM) is ubiquitous and plays an important role in regulating water quality, ecological function, and the fate and transport of trace elements and pollutants in aquatic environments. Both the colloidal precursors (i.e. <1 kDa) and bulk DOM collected from a freshwater estuary were incubated in the dark for 21 days to examine dynamic changes in molecular size and composition induced by microbial degradation and self-assembly. Results showed that the concentrations of total organic carbon, carbohydrates, and protein-like substances decreased by 11–30% during incubation, while those of humic- and fulvic-like substances remained relatively constant, indicating humic substances are more resistant to microbial utilization compared to carbohydrates and protein-like DOM. Despite the different extents in decline, these DOM components had a similar transformation pathway from the <1 kDa to colloids (1 kDa–0.45 μm) and further to microparticles (>0.45 μm). Overall, carbohydrates and protein-like substances, especially the high molecular weight components, were preferentially decomposed by microorganisms whereas humic- and fulvic-like DOM components significantly coagulated through abiotic self-assembly. The contrasting degradation/transformation pathways between the humic-like and protein-like substances along the size continuum, as also characterized by flow field-flow fractionation analysis, demonstrated that the dynamic transformation and degradation of DOM is regulated by both molecular size and organic composition. This finding provides new insights into the biogeochemical cycling pathways of heterogeneous DOM and its environmental fate and ecological role in aquatic systems.

Synthesis and Conjugation of Alkyne‐Functional Hyperbranched Polyglycerols

This study outlines the synthetic and purification process used to obtain hyperbranched polyglycerol (HPG) within a molecular weight range not previously obtainable. Purified fractions with low polydispersity are achieved via successive precipitations from acetone. Furthermore, the use of the initiator molecule 5‐hexyne‐1‐ol introduces alkyne functionality at the core of each HPG molecule. Alkyne‐azide cycloaddition chemistry in combination with NMR and field flow fractionation analysis is used to verify the availability of the alkyne core for bioconjugation across the range of molecular weights. image

IgG-loaded hyaluronan-based dissolving microneedles for intradermal protein delivery

Dissolving microneedles are an attractive approach for non-invasive delivery of drugs via the skin, particularly when the doses are in the microgram or low-milligram range. The aim of the study was to develop hyaluronan-based, monoclonal IgG-loaded microneedles for intradermal delivery enabling efficient penetration and rapid dissolution in the skin while preserving protein stability. Microscopic analysis showed successful preparation of sharp microneedles with the tip length of ~280μm and with up to 10% (w/w) of IgG content. The water content of the microneedles was ~12% and was not affected by the protein content. The protein distribution was uniform within microneedle tips and individual arrays but some array-to-array variation of IgG level within a single preparation batch was detected. After dissolution of microneedle arrays in PBS, >80% of protein was recovered and no conformational changes were detected by fluorescence spectroscopy. At submicron level, only weak and reversible interaction between HA and IgG was found by asymmetric flow field flow fractionation analysis after the dissolution of prepared microneedles. Although, the formation of insoluble micron-size particles was detected by flow imaging microscopy the IgG amount incorporated into these particles was negligible (<5%). Finally, microneedles were able to penetrate into the epidermis of ex vivo human skin followed by the rapid dissolution of the microneedle tips in the skin. After 10min of application, the majority of the original tip length was dissolved and IgG and hyaluronan were co-deposited until a depth of 150–200μm in the skin. In conclusion, developed hyaluronan-based dissolving microneedles allow rapid non-invasive intradermal protein delivery.

Asymmetrical flow field-flow fractionation analysis of water suspensions of polymer nanofibers synthesized via RAFT-mediated emulsion polymerization

The aim of this work is to present a method based on asymmetric flow-field-flow-fractionation coupled on-line to a static light scattering (AF4-UV-SLS) detector to characterize self-assembled nanofibers (NFs). The method developed herein allows the determination of both the length distribution of the NFs as well as the distribution in terms of aggregation number per unit length (Agg). Given the remaining synthetic challenges of better controlling the structural homogeneity and particle dimensions, the NF length and aggregation number per unit length are becoming essential for the improvement and control of their chemical processes and a better understanding of their properties. The results obtained with this AF4-UV-SLS method indicate that a well-resolved NF length distribution characterization and Agg determination were attained. These results provide critical information concerning the physical properties of the investigated NFs and open the door to the characterization of new self-assembled polymers with various asymmetrical architectures.

Characterization of natural organic matters using flow field-flow fractionation and its implication to membrane fouling

ABSTRACT Transport and deposition characteristics of natural organic matter (NOM) are systematically investigated using flow field-flow fractionation (Fl-FFF) at various chemical and physical conditions. Humic acid (HA) was chosen as model organic foulants. Prior to Fl-FFF analysis, HA was fractionated by membranes with different molecular weight cut-offs. To elucidate physicochemical factors affecting the deposition and transport characteristics of organic foulants, various concentrations of NaCl (i.e. up to seawater level) and CaCl2 were employed as carrier solutions in Fl-FFF. Each fractionated NOM showed different transport and deposition characteristics with respect to the chemical and physical conditions employed during Fl-FFF analysis. When the total dissolved solids (TDS) concentration increased, there was more significant variation in the retention time for large NOM fractions compared with small NOM fractions. This means that the transport and deposition tendency of the larger NOM fractions vari...

Comparison of on-line detectors for field flow fractionation analysis of nanomaterials

Characterization of nanomaterials must include analysis of both size and chemical composition. Many analytical techniques, such as dynamic light scattering (DLS), are capable of measuring the size of suspended nanometer-sized particles, yet provide no information on the composition of the particle. While field flow fractionation (FFF) is a powerful nanoparticle sizing technique, common detectors used in conjunction with the size separation, including UV, light-scattering, and fluorescence spectroscopy, do not provide the needed particle compositional information. Further, these detectors do not respond directly to the mass concentration of nanoparticles. The present work describes the advantages achieved when interfacing sensitive and elemental specific detectors, such as inductively coupled plasma atomic emission spectroscopy and mass spectrometry, to FFF separation analysis to provide high resolution nanoparticle sizing and compositional analysis at the μg/L concentration level, a detection at least 10–100-fold lower than DLS or FFF–UV techniques. The full benefits are only achieved by utilization of all detector capabilities, such as dynamic reaction cell (DRC) ICP–MS. Such low-level detection and characterization capability is critical to nanomaterial investigations at biologically and environmentally relevant concentrations. The techniques have been modified and applied to characterization of all four elemental constituents of cadmium selenide–zinc sulfide core–shell quantum dots, and silver nanoparticles with gold seed cores. Additionally, sulfide coatings on silver nanoparticles can be detected as a potential means to determine environmental aging of nanoparticles.

The role of nanominerals and mineral nanoparticles in the transport of toxic trace metals: Field-flow fractionation and analytical TEM analyses after nanoparticle isolation and density separation

Nanominerals and mineral nanoparticles from a mining-contaminated river system were examined to determine their potential to co-transport toxic trace metals. A recent large-scale dam removal project on the Clark Fork River in western Montana (USA) has released reservoir and upstream sediments contaminated with toxic trace metals (Pb, As, Cu and Zn), which had accumulated there as a consequence of more than a century and a half of mining activity proximal to the river’s headwaters near the cities of Butte and Anaconda. To isolate the high-density nanoparticle fractions from riverbed and bank sediments, a density separation with sodium polytungstate (2.8g/cm3) was employed prior to a standard nanoparticle extraction procedure. The stable, dispersed nanoparticulate fraction was then analyzed by analytical transmission electron microscopy (aTEM) and flow field-flow fractionation (FlFFF) coupled to both multi-angle laser light scattering (MALLS) and high-resolution, inductively coupled plasma mass spectrometry (HR-ICPMS). FlFFF analysis revealed a size distribution in the nano range and that the elution profiles of the trace metals matched most closely to that for Fe and Ti. aTEM confirmed these results as the majority of the Fe and Ti oxides analyzed were associated with one or more of the trace metals of interest. The main mineral phases hosting trace metals are goethite, ferrihydrite and brookite. This demonstrates that they are likely playing a significant role in dictating the transport and distribution of trace metals in this river system, which could affect the bioavailability and toxicity of these metals.

A study on the infl uence of ionic strength on the elution behaviour of membrane organic foulant using advanced separation tools

Although membrane technology has become a reliable and viable alternative for water and wastewater treatment, membrane fouling is a serious challenge. In this case study, we report application of different techniques to extract foulant from the hollow fibre membrane and characterize the foulant into various components of organic, inorganic and different fractions. The organic foulant was subjected to high-pressure size exclusion chromatography (HPSEC) and flow field-flow fractionation (FlFFF) analysis to study the influence of ionic strength on its elution behaviour using NaCl and CaCl2 as carrier solutions. It was observed that an increase in ionic strength delayed the elution time of both the organic foulant and the Na-salt of Polysterene sulphone (PSS) with HPSEC. However, no such effect was observed with FlFFF analysis. Such study is significant because the characteristics of the membrane organic foulant are believed to be influenced by the carrier ionic conditions and pH and, therefore their subsequent interaction with the membrane and membrane fouling process. However with FlFFF, whether the influence of carrier ionic strength is limited to certain type of ionic carriers or certain groups of natural organic matter is a scope for further research.

Size fractionation and optical properties of colloids in an organic-rich estuary (Thurso, UK)

The optical characteristics of a black water river estuary from the north coast of Scotland were examined in the filtered (0.4 µm), ultrafiltered (5 kDa) and colloid-enriched fractions of estuarine samples. The samples were collected over the full salinity range during a period when the pH was relatively constant (8.2–8.5) throughout the estuary, allowing the influence of salinity on estuarine colloidal processes to be distinguished. The properties examined in the bulk, the low molecular weight (LMW) and the colloidal fraction (HMW) were UV–visible absorption, 3-D fluorescence excitation–emission matrix (EEM) spectrum, inorganic and organic carbon, mean size (by dynamic light scattering), and size distribution by flow field-flow fractionation analysis (FlFFF). The combined results of these analyses support the view that river-borne, humic-rich colloids underwent two types of transformation upon mixing with the seawater end member. The first one resulted in an apparent increase in the abundance of LMW constituents and may be explained by coiling of the individual humic macromolecules. The second one resulted in an increase in the mean size measured in both the lower and higher colloidal size ranges, and may be explained by aggregation of colloids to form entities that were still mostly colloidal i.e., smaller than 0.4 µm. The LMW contribution to the bulk optical properties increased with increasing salinity. Very similar findings were obtained from simulated mixing experiments using a Nordic Reference NOM extract as a source of freshwater colloids. This indicates that changes in the molecular architecture and molar mass of river-borne colloids—not changes in their chemical nature—were responsible for the observed variations in the spectral characteristics of CDOM in this estuary.

Maleimide conjugation markedly enhances the immunogenicity of both human and murine idiotype-KLH vaccines

The collection of epitopes present within the variable regions of the tumor-specific clonal immunoglobulin expressed by B cell lymphomas (idiotype, Id) can serve as a target for active immunotherapy. Traditionally, tumor-derived Id protein is chemically conjugated to the immunogenic foreign carrier protein keyhole limpet hemocyanin (KLH) using glutaraldehyde to serve as a therapeutic vaccine. While this approach offered promising results for some patients treated in early clinical trials, glutaraldehyde Id-KLH vaccines have failed to induce immune and clinical responses in many vaccinated subjects. We recently described an alternative conjugation method employing maleimide–sulfhydryl chemistry that significantly increased the therapeutic efficacy of Id-KLH vaccines in three different murine B cell lymphoma models, with protection mediated by either CD8 + T cells or antibodies. We now define in detail the methods and parameters critical for enhancing the in vivo immunogenicity of human as well as murine Id-KLH conjugate vaccines. Optimal conditions for Id sulfhydryl pre-reduction were determined, and maleimide Id-KLH conjugates maintained stability and potency even after prolonged storage. Field flow fractionation analysis of Id-KLH particle size revealed that maleimide conjugates were far more uniform in size than glutaraldehyde conjugates. Under increasingly stringent conditions, maleimide Id-KLH vaccines maintained superior efficacy over glutaraldehyde Id-KLH in treating established, disseminated murine lymphoma. More importantly, human maleimide Id-KLH conjugates were consistently superior to glutaraldehyde Id-KLH conjugates in inducing Id-specific antibody and T cell responses. The described methods should be easily adaptable to the production of clinical grade vaccines for human trials in B cell malignancies.

Partitioning and stability of engineered ZnO nanoparticles in soil suspensions using flow field-flow fractionation

Environmental context. Nanoparticulate materials are increasingly being used as catalysts and lubricants, for pollution control and drug delivery, and in electronics, fabrics, cosmetics and sunscreens. In spite of this growth, information about the fate and toxicity of nanoparticles in the environment is limited, partly due to the lack of techniques capable of measuring nanoparticles in complex environmental matrices. One emerging tool, flow field-flow fractionation, can be used to determine the presence and particle size distribution of engineered nanoparticles, for example in soil pore waters, thereby enhancing our understanding of their environmental fate and impacts. Abstract. This paper reports preliminary results for the determination of engineered ZnO nanoparticles using flow field-flow fractionation (FlFFF). This separation technique was used to determine the particle size distributions (PSDs) of ZnO nanoparticles spiked in soil suspensions. Before FlFFF analysis, the soil was prepared in suspension form, shaken overnight and gravitationally settled to extract the &lt;1-µm fraction. The effect of aging was also investigated using soil samples incubated with known concentrations of ZnO nanoparticles for 7 and 14 days. The results show that FlFFF can be used to determine the PSD of engineered nanoparticles and monitor their partitioning and stability in soil suspensions.

Characterization of protein aggregation: The case of a therapeutic immunoglobulin

In this paper, a therapeutic immunoglobulin (Antibody A) has been characterized in two solutions: (1) 0.1% acetic acid containing 50 mM magnesium chloride, a solution in which the immunoglobulin is stable, and (2) 10 mM sodium phosphate buffer pH ∼ 7. The protein solutions were characterized by microscopy, asymmetrical flow field-flow fractionation (FFF), light scattering, circular dichroism, fluorescence and fluorescence lifetime spectroscopy. The results show that Antibody A dissolved in 0.1% acetic acid containing 50 mM magnesium chloride exists as 88% monomer, 2% low molecular weight aggregates and 10% high molecular weight aggregates (> 1 million Dalton). In phosphate buffer, Antibody A formed micrometre-sized aggregates that were best characterized by fluorescence microscopy. The aggregation of Antibody A in phosphate buffer was shown to be concomitant with conformational changes in amino acid residue side chains. The aggregates formed in phosphate buffer were easily disrupted during FFF analysis, indicating that they are formed by weak interactions. The combination of microscopy, asymmetrical flow field-flow fractionation (FFF) and spectroscopy allowed a reliable assessment of protein self association and aggregation.

Preferential adsorption of fluorescing fulvic and humic acid components on activated carbon using flow field-flow fractionation analysis.

Activated carbon treatment of drinking water is used to remove natural organic matter (NOM) precursors that lead to the formation of disinfection byproducts. The innate hydrophobic nature and macromolecular size of NOM render it amenable to sorption by activated carbon. Batch equilibrium and minicolumn breakthrough adsorption studies were performed using granular activated carbon to treat NOM-contaminated water. Ultraviolet (UV) absorption spectroscopy and flow field-flow fractionation analysis using tandem diode-array and fluorescence detectors were used to monitor the activated carbon sorption of NOM. Using these techniques, it was possible to study activated carbon adsorption properties of UV absorbing, fluorescing and nonfluorescing, polyelectrolytic macromolecules fractionated from the total macromolecular and nonmacromolecular composition of NOM. Adsorption isotherms were constructed at pH 6 and pH 9. Data were described by the traditional and modified Freundlich models. Activated carbon capacity and adsorbability were compared among fractionated molecular subsets of fulvic and humic acids. Preferential adsorption (or adsorptive fractionation) of polyelectrolytic, fluorescing fulvic and humic macromolecules on activated carbon was observed. The significance of observing preferential adsorption on activated carbon of fluorescing macromolecular components relative to nonfluorescing components is that this phenomenon changes the composition of dissolved organic matter remaining in equilibrium in the aqueous phase relative to the composition that existed in the aqueous phase prior to adsorption. Likewise, it changes the composition of dissolved organic matter remaining in equilibrium in the aqueous phase relative to the adsorbed phase. This research increases our understanding of NOM interactions with activated carbon which may lead to improved methods of potable water production.

Size analysis of automobile soot particles using field-flow fractionation.

Soot particles emitted from various automobile engines are analyzed for size distributions using field-flow fractionation (FFF). Soot samples are prepared for FFF analysis using a three-step procedure, where a layer of soot particles is focused between the layers of n-hexane and water, followed by dispersing of particles in water containing 0.05% Triton X-100. The mean diameters determined by FFF show similar trends with those obtained from dynamic light scattering (DLS) and scanning electron microscopy (SEM). Data from FFF are also compared with those from an on-line scanning mobility particle sizer (SMPS). SMPS size distributions extend further to larger size than those of FFF distributions, which indicates the three-step sample preparation procedure effectively disaggregates the agglomerated particles. Although the amount of particulate matter (PM) emitted from a heavy-duty diesel engine is much higher than that from a light-duty diesel engine, the size distributions of soot particles show no significant difference between heavy- and light-duty diesel engines. The engine-operating mode (engine speed and load rate) does not seem to affect significantly the size distribution of soot particles. It was found that the PM from a turbocharged diesel engine contains a higher percentage of particles smaller than 100 nm than an engine with a naturally aspirated (NA) air-inhalation system. As for gasoline engines, the PM collected after the catalytic converter has a narrower size distribution than those collected before and has a higher percentage of particles smaller than 100 nm.

Size Determination of Diesel Soot Particles Using Flow and Sedimentation Field-Flow Fractionation

The applicability of field-flow fractionation (FFF) was investigated for determination of size and size distribution of diesel soot particles. A sample preparation procedure was developed for FFF analysis where soot particles are recovered from filters in an ethanol bath sonicator, and then they are dispersed in water containing 0.05% Triton X-100 and 0.02% NaN(3). Mean diameters obtained from sedimentation FFF (SdFFF) and flow FFF (FlFFF) agree well with each other and are in good agreement with diameters obtained from photon correlation spectroscopy (PCS) and scanning electron microscopy. The relative error was less than 11%. Data show diesel soot particles have broad size distributions ranging from 0.05 up to ∼0.5 μm with the mean diameters between 0.1 and 0.2 μm. The use of FlFFF is more convenient as FlFFF fractograms can be converted directly to size distributions, while the conversion of the SdFFF fractogram needs the particle density information. The density needed for SdFFF analysis was obtained by combining the SdFFF retention data with the PCS size data. For samples whose density is known, SdFFF may be more useful as SdFFF provides a wider dynamic range than FlFFF under constant field strength.