Size Distribution Of Colloids Research Articles

Probing particle size distributions in natural surface waters from 15 nm to 2 μm by a combination of LIBD and single-particle counting

We present a technique for measuring colloid size distributions between 15 nm and 2 μm at concentrations relevant to natural surface waters. Two particle-measuring methods are combined: laser-induced breakdown detection (LIBD), which allows the quantification of colloid size distributions below 400 nm, and a commercial single-particle counter that extends the accessible size range up to two μm. Centrifugation was used in order to separate micrometer sized particles for the LIBD measurement. The feasibility is demonstrated on water of Lake Brienz (Switzerland) and the River Pfinz (Germany) and the particle size distributions follow Pareto's law even down to 15 nm in both cases.

Fluorescence variability of marine and terrestrial colloids: Examining size fractions of chromophoric dissolved organic matter in the Damariscotta River estuary

Marine chromophoric dissolved organic matter (CDOM) imparts highly variable optical signatures in surface waters over short spatial and temporal scales, but the cause of that variability is poorly understood. A major fraction of dissolved organic matter in seawater is colloidal in size and can cycle quite rapidly, potentially contributing to the observed variability in CDOM. The relationship between marine colloids and CDOM optical variability was examined using flow field-flow fractionation (FlFFF) to partition the colloidal organic phase into a continuum of molecular sizes for optical characterization by excitation emission matrix spectroscopy (EEMS). Colloidal organic matter in surface seawater of the Damariscotta River estuary showed 2 major peaks in apparent abundance, spanning at ∼ 1–5 kDa and ∼ 15–150 kDa in size, respectively. The relative magnitude of these peaks changed systematically with the phase of phytoplankton blooms during 2003 and 2004, implying a relationship between colloid size distribution and bloom dynamics. Of the two colloidal sizes, the 1–5 kDa fraction was far more variable in apparent abundance than the larger colloidal matter. EEMS results reveal a compositional partitioning of protein-like and humic-like fluorescence between size fractions. Protein-like materials occurred primarily in the smallest colloid size fraction while humic-type materials resided mainly in the larger colloidal phase. These findings suggest that the fluorescence signature of bulk dissolved organic matter results from a collage of chromophores having optical characteristics that differ according to size of the molecular constituents. The colloidal-sized fluorescence characteristics of marine derived CDOM were contrasted with bulk CDOM to provide fundamental information on the distribution and forms of CDOM in Maine coastal waters. The findings here indicate that colloidal processes will have significant effects on the character and variability in the optical signature of surface seawaters.

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.

Particle‐Size and Element Distributions of Soil Colloids

Transport of colloids (diameter < 1 μm) through soil has implications for both horizon development and contaminant mobility. Colloid physical properties (size, shape), mineralogy, and surface chemistry are known to influence transport and deposition. Sedimentation field‐flow fractionation‐inductively coupled plasma–mass spectrometry (Sd FFF‐ICP–MS) was used to examine size and element composition distributions of colloids collected from the profile of a texture‐contrast soil located in South Australia. The morphology of the colloids was also examined by transmission electron microscopy (TEM). Colloids collected from the soil matrix, the source of mobile colloids, had significant differences in the size distributions among the three horizons sampled. These differences were consistent with long‐term soil formation processes. Colloids mobilized by rainfall, which were collected from overland flow and infiltration through the soil profile, all showed very similar size distributions. This is consistent with the presence of preferential flow paths and suggests that colloids, and colloid‐associated contaminants, can be transported rapidly through the vadose zone with minimal interaction with the soil matrix. The Sd FFF‐ICP–MS analysis showed variation in element ratios (Fe/Al, Mg/Al), which were used to detect changes in surface coatings and mineralogy over the colloid size range. The study demonstrated the utility of Sd FFF‐ICP–MS for examining the influence of colloid size on element composition and on elucidating colloid transport processes in soils.

High resolution ICPMS as an on-line detector for flow field-flow fractionation; multi-element determination of colloidal size distributions in a natural water sample

Results are described from the first application of high resolution ICPMS coupled to flow field-flow fractionation (FlFFF–HR ICPMS), for the elemental characterization of small colloidal material (1–50 nm hydrodynamic diameter) in a natural freshwater sample. Detection limits for a 45 mL preconcentrated sample were 200 ng L −1 to 5 μg L −1 for major elements, 1–30 ng L −1 for most of the first row transition elements and <1 ng L −1 for rare earth elements. R.S.D. of the concentrations determined in five replicate measurements were less than 10% for 42 of the elements quantified. In total, 45 elements could be quantified, 15 more than were quantified in an earlier study performed with a quadrupole ICPMS. Direct on-channel preconcentration was used and the degree of preconcentration necessary was examined. The linearity between sample volume and calculated colloidal concentrations was good, but possible indications of sample losses were observed. Peak deconvolution analysis was carried out on some elements in order to obtain an estimate of the distribution of elements between organic carbon- and iron-rich colloids. Among the elements not previously studied, P, V and Ti were shown to associate strongly to iron-rich colloids, Br and I were exclusively bound to organic carbon colloids while As and Cd were equally distributed between the two. Sc corresponded to the pattern of lanthanides and Cr to the pattern of the other first row transition elements.

Measuring multimodal size distributions of aquatic colloids at trace concentrations

Many applications in research as well as industry require a highly sensitive detection of particulate matter in water or process liquids. We present a technique to measure the distribution of colloid sizes between 20 and 100nm in situ at ultratrace concentrations. The method is based on laser-induced breakdown detection, which has been applied for trace detection of colloids and determination of the weighted mean size. Using a refined method of data evaluation, we are now able to measure the number density of inorganic colloids in six size classes between 20 and 100nm simultaneously below ppb concentration.

Physical investigations of a ferrofluid based on hydrocarbons

Since in future the applications of the magnetic fluids will focus more toward the biological uses, where the ultra-fine ferrophase is particularly important for the penetration of the cell structures, the size distribution of the magnetic colloids remains a major problem, as in the case of the ferrofluid analyzed here. The electron microscopy, the thermogravimetric investigation and the infrared spectral analysis evidenced some of the physical features that are essential for its small diameter size.

The feasibility of inert colloidal processing of silicon nanoparticles

Silicon nanoparticles have important applications, including nonvolatile floating-gate memory devices. To prevent device performance variations, particle size and oxide thicknesses need to be controlled with a high degree of precision. Additionally, producing well-ordered, two-dimensional arrays of nanoparticles may require the exploitation of self-assembly techniques and colloidal forces, which in turn requires that silicon nanoparticles first come into contact with liquids. Until recently, aerosol silicon nanoparticle collection into liquid was assumed to be an inert process. Once formed, the silicon nanoparticle colloid was assumed to be inert. In fact, silicon nanoparticles produced in the aerosol phase by dilute silane pyrolysis and size classified with a differential mobility analyzer undergo a size reduction upon collection in ethylene glycol, water, and ethanol. Unclassified polydisperse silicon aerosol nanoparticles with an average diameter of 11 nm become monodisperse when collected in a colloid and have a final particle diameter of 2–5 nm. Further evidence suggests that silicon nanoparticles collected in ethanol react with the ethanol to produce tetraalkylorthosilicate-like species. Collections of aerosol silicon nanoparticles in degassed water do not show measurable differences between the aerosol and colloidal size distributions. This reduced reactivity to the solvent indicates that the presence of dissolved oxygen in the solvent may be responsible for the reactivity between the silicon nanoparticles and the solvent.

Stream-Subsurface Exchange of Zinc in the Presence of Silica and Kaolinite Colloids

The mobility of sorbing contaminants in surface waters often depends strongly on associations with sediments, including both fine suspended particles and stationary bed sediments. Hydrodynamic flow coupling causes an exchange of dissolved and suspended substances between streams and underlying pore waters (hyporheic exchange). As a result, the fate of many pollutants is expected to be greatly influenced bythe flux of colloids and contaminants across the stream-subsurface interface and the interactions of both types of substances with the bed sediments. Herein, we present experimental results on the stream-subsurface exchange of zinc in the presence of colloidal silica and kaolinite in a laboratory flume. We also apply a process-based theoretical model to predict the coupled transport of colloids and reactive solutes. Model input parameters were obtained using independent batch and column experiments. Zinc immobilization in the bed was found to be significantly greater in the presence of kaolinite than in the presence of colloidal silica. Model predictions indicated that there were two distinct reasons for the greater zinc immobilization in the presence of kaolinite: zinc sorbed more strongly to kaolinite than to silica, and kaolinite particles also deposited more readily in the streambed than did silica colloids. Model simulations were found to be highly dependent on the colloid size distribution. When the colloids had a bimodal distribution, colloidal-phase contaminant transport occurred primarily on the finer fraction, but bulk colloid deposition was dominated by removal of the coarser fraction.

The colloidal size spectrum of CDOM in the coastal region of the Mississippi Plume using flow field-flow fractionation

Chromophoric dissolved organic matter (CDOM) is a major component of the total dissolved organic matter in seawater, and it can interfere significantly with oceanographic remote sensing in nearshore waters. Coastal marine CDOM comprises an undefined, likely rapidly changing mixture of terrestrially and marine-derived substances. Flow Field-Flow Fractionation (FlFFF) offers a novel approach for separating the colloidal (high molecular weight) fraction of CDOM into broad size continuums that can offer insights to the characteristics and reactivity of CDOM constituents. FlFFF analyses of seawaters in and around the Mississippi Plume were performed during high and low flow conditions and the results compared to analyses of phytoplankton cultures and waters from a coastal estuary having low freshwater inputs. FlFFF fractograms displayed major differences in the size distribution of CDOM between offshore in the Gulf of Mexico (GOMex) and the Mississippi River plume. Colloidal size distributions in nearshore surface waters out of the immediate influence of the Mississippi Plume contained a mixture of features seen in offshore waters, plume waters, and in phytoplankton cultures. Plume waters had a high abundance of larger colloidal phases but continued dilution with coastal waters led to preferential losses of mid-sized colloidal matter. Colloidal size spectra in offshore waters of the GOMex during spring were similar to that observed in estuarine waters after the spring bloom. These preliminary findings suggest that the colloidal size spectrum of CDOM may provide information on its provenance and the relative mixtures of terrestrial and marine components.

Laser-induced breakdown detection combined with asymmetrical flow field-flow fractionation: application to iron oxi/hydroxide colloid characterization

The combination of asymmetrical flow field-flow fractionation (AsFlFFF) with the laser-induced breakdown detection (LIBD) is presented as a powerful tool for the determination of colloid size distribution at trace particle concentrations. Detection limits (Dl) of 1, 4, and 20 μg/L have been determined for a mixture of polystyrene reference particles with 20, 50, and 100 nm in size, respectively. This corresponds to injected masses of 1, 4, and 20 pg, which is lower than found in a previous study with the symmetrical FlFFF (SyFlFFF). The improvement is mainly due to the lower colloid background discharged from the AsFlFFF channel. The combined method of AsFlFFF–LIBD is then applied to the analysis of iron oxi/hydroxide colloids being considered as potential carriers for the radionuclide migration from a nuclear waste repository. Our LIBD arrangement is less sensitive for iron colloid detection as compared to reference polystyrene particles which results in a detection limit of ∼240 μg/L FeOOH for the AsFlFFF–LIBD analysis. This is superior to the detection via UV-Vis absorbance and comparable to ICP-MS detection. Size information (mean size 11–18 nm) for different iron oxi/hydroxide colloids supplied by the present method is comparable to that obtained by sequential ultrafiltration and dynamic light scattering. A combined on-line ICP-MS detection is used to gain insight into the colloid-borne main and trace elements.

Competition between iron- and carbon-based colloidal carriers for trace metals in a freshwater assessed using flow field-flow fractionation coupled to ICPMS

Flow field–flow fractionation (FlFFF) coupled to an inductively coupled plasma mass spectrometer (ICPMS) has been used to determine the chemical composition of colloids from a freshwater sample as a function of size. Organic carbon and iron are the most abundant colloidal components, and are considered as the major carrier phases for other chemical elements present. The size distribution of organic carbon colloids shows a single peak with an estimated hydrodynamic diameter between 1 and 1.5 nm, while the iron colloids show a more complex distribution centred at larger colloid sizes with estimated hydrodynamic diameters up to 5 nm. The association of 32 trace elements with these two carrier colloids has been quantified by deconvolution analysis, and the resulting distributions are shown to be chemically consistent. The observed distributions are also shown to be broadly consistent with predictions from speciation modelling for the subset of 8 elements for which appropriate stability constants are available.

Polymer-protected palladium nanoparticles. Morphologies and catalytic selectivities

Colloidal palladium nanocatalysts prepared by in situ reductions of palladium chloride were immobilized and protected by either of two water-soluble polymers. The particle sizes and size distributions of the palladium colloids were determined by transmission electron microscopy. Their selectivities as catalysts were determined by comparing the extents of hydrogenation of carefully chosen pairs of small-molecule olefins. There was found to be high hydrogenation selectivity with regard to cyclic vs. noncyclic olefins. Selectivity was relatively low, however, among olefins that differed only in size (such as hexene vs. octene), or olefins differing only with regard to the positions of the double bonds (such as 1-octene vs. 3-octene). Selectivity could be improved by careful choice of the immobilizing polymer, and by its use at relatively high concentrations.

Size distribution of colloidal silica in sodium silicate solutions investigated by dynamic light scattering and viscosity measurements

Three types of aqueous sodium silicate solutions characterized by molar SiO 2:Na 2O ratios of 2.2, 3.3, and 3.9 were investigated by dynamic light scattering and viscosity measurements. The solutions were prepared by diluting concentrated commercial products to SiO 2 content between 0.5 and 15 wt%. Dynamic light scattering (DLS) was used for the investigation of size distributions of colloids immediately after dilution. At least three size classes of colloidal particles were detected, which exist in parallel in the solutions. The respective radii are 0.4 to 0.6 nm, 2.5 to 13 nm, and 75 to 85 nm. The larger colloids dominate the mass distribution, whereas the smaller colloids control the surface area of the colloidal fraction. Material properties such as pH, viscosity, refractive index, and density were measured as a function of dilution. The evaluation of the viscosity data indicated that the colloids have a lower density than dense amorphous silica. Aging effects could be suppressed by measuring within 1 h after dilution.

Measurement of the size and structure of natural aquatic colloids in an urbanised watershed by atomic force microscopy

Atomic force microscopy (AFM) in tapping mode was used to determine the conformation of humic substances and aquatic colloids from rivers in an urban catchment in the West Midlands, U.K. Hurnie macromolecules were shown to have a size of about 1–3 nm in agreement with the literature, indicating that the preparation methods and the AFM were both performing satisfactorily. Three types of natural aquatic colloids were observed by AFM. Firstly, a surface coating about 1–5 nm thick, likely composed of organic and oxide material flattened by drying and interaction with the AFM tip. Secondly, small irregular, globular material between 1 and 70 nm in size, again most likely made of oxide and organic material. Lastly, fibrillar material was present which was 1–10 nm in diameter and 10–1000 nm in length. Most likely this material was microbially produced (muco-) polysaccharides. Size distributions of colloids from all samples, regardless of sample site and sample preparation, indicated colloids with a fairly low polydispersity and with particle numbers dominated by material < 10 nm.

The iron status in colloidal matter from the Rio Negro, Brasil

Colloidal and particulate natural organic matter was size-fractionated and concentrated from the Rio Negro river using tangential-flow filtration (TFF). Flow field-flow fractionation (F-FFF), with UV absorbance detection (UVA), was used to investigate the molecular weight distributions of the organic colloids. To further characterize the nature of the Rio Negro colloids, the size distributions of the iron concentrations were determined by direct on-line coupling of the F-FFF to an inductively coupled plasma emission spectrometer (ICP-AES). The size distributions obtained by both F-FFF-UVA and F-FFF-ICP-AES were considerably smaller than expected from the stated pore size of the TFF membranes. These results demonstrate that care must be taken in using TFF to classify the size distribution of organic colloids and associated elements present in rivers. The iron distribution is more closely correlated to the organic matter distribution in the colloidal fraction than in the particulate fraction, but it is shifted towards heavier molecular weights for both fractions. The combination of electron paramagnetic resonance spectroscopy (EPR) and transmission electron microscopy (TEM) reveals the presence of iron occurring as: specific complexes with organic functional groups, as Fe-oxide/oxihydroxide phases, or as structurally incorporated component in kaolinite. Particulate and colloidal fractions are differentiated from each other with respect to the iron forms, which is in qualitative agreement with the F-FFF-ICP-AES results.

Use of single particle counters for the determination of the number and size distribution of colloids in natural surface waters

Abstract Particle size distribution (PSD) is a fundamental physical property, which should be measured to understand the role of the colloids in the biogeochemical cycle of aquatic contaminants. The single particle counter (SPC) is an instrument designed to precisely determine sub-micron PSD. The advantages of this system are: to give an absolute colloid number concentration, to measure without bias highly polydispersed samples, to avoid artefacts resulting from sample pre-concentration, to be transportable, allowing on-site measurements. This study presents the results of the methodological work done on our SPC, a 2-counter (one monitor and spectrometer) based system including a precision pump for sample injection and dilution. This system is able to count and size colloids from 50 nm to 2 μm into 19 size classes. Calibration work was performed with standard latex beads and natural samples from various surface waters. The quantification limit on the colloid number concentration for the smallest (50–100 nm), the medium (400–500 nm) and the largest (>2 μm) size classes are 1.0×104, 1.1×102 and 18 ml−1, respectively. Instrument saturation occurs at 8×108 ml−1 for the 50–100 size class, and at 2×103 ml−1 for medium and highest size classes. The relative repeatability varies between 7 and 29% for the different size classes in a synthetic, polydispersed sample reproducing typical environmental colloid concentration. These values are not significantly different from the with-in replicates variability. The verification of the factory calibration shows that measured concentrations are between 27 and 106% of the nominal concentration of standards. In conclusion, the presented SPC system gives reliable results of colloid number concentration and size distribution in a wide range of natural surface waters and offers new opportunities for on-site studies.

Aquatic colloids relevant to radionuclide migration: characterization by size fractionation and ICP-mass spectrometric detection

The application of the flow-field flow fractionation (FFFF) combined with on-line ICP-mass spectrometry (ICP-MS) to the characterization of aquatic colloids is described. The capabilities and drawbacks of the technique are discussed with the aid of two examples. (1) The size distribution of smectitic colloids dispersed from a natural bentonite is determined by FFFF and laser light scattering (LLS) and compared with the size information obtained by ICP-MS detection. Due to the pronounced size dependency of the scatter light intensity, the LLS detection tends to overestimate the larger sized particles. Therefore, the FFFF-ICP-MS fractogram delivers more reliable size information. (2) Groundwater humic/fulvic colloids and the humic matter extracted from the corresponding sediment, both taken from the Gorleben aquifer (Lower Saxony, Northern Germany), are analysed by FFFF-ICP-MS. The location of REE, U, Th and Ca in different colloid size fractions appears to be very similar in both samples. The element specific fractograms suggest in agreement with earlier studies the location of Th and the REE mainly in inorganic colloids>17 nm containing also Fe and/or Al. U and Ca appear to be distributed between larger colloids and the fulvic/humic acid fraction with a size <3 nm. The results demonstrate that even in groundwater/sediment systems with high humic/fulvic content, inorganic colloids may play an important role as carrier for polyvalent metal ions. The consequences of this finding on the applicability of in-situ K d values for U, Th and REE, taken as naturally abundant representatives of the nuclear waste derived actinides, for the assessment of laboratory sorption data is discussed.

Physical factors affecting the transport and fate of colloids in saturated porous media

Saturated soil column experiments were conducted to explore the influence of colloid size and soil grain size distribution characteristics on the transport and fate of colloid particles in saturated porous media. Stable monodispersed colloids and porous media that are negatively charged were employed in these studies. Effluent colloid concentration curves and the final spatial distribution of retained colloids by the porous media were found to be highly dependent on the colloid size and soil grain size distribution. Relative peak effluent concentrations decreased and surface mass removal by the soil increased when the colloid size increased and the soil median grain size decreased. These observations were attributed to increased straining of the colloids; i.e., blocked pores act as dead ends for the colloids. When the colloid size is small relative to the soil pore sizes, straining becomes a less significant mechanism of colloid removal and attachment becomes more important. Mathematical modeling of the colloid transport experiments using traditional colloid attachment theory was conducted to highlight differences in colloid attachment and straining behavior and to identify parameter ranges that are applicable for attachment models. Simulated colloid effluent curves using fitted first‐order attachment and detachment parameters were able to describe much of the effluent concentration data. The model was, however, less adequate at describing systems which exhibited a gradual approach to the peak effluent concentration and the spatial distribution of colloids when significant mass was retained in the soil. Current colloid filtration theory did not adequately predict the fitted first‐order attachment coefficients, presumably due to straining in these systems.

Laser induced breakdown detection for the assessment of colloid mediated radionuclide migration

Colloids play an important role in the transport of pollutants in the environment. Harmful substances can undergo transport over large distances if bound to colloids in aqueous surrounding. One important example is the migration of Pu(IV) at unexpectedly high rates over several miles at a Nevada nuclear detonation test site. For long term safety assessments of radioactive waste repositories, it is hence crucial to know about the amount, size distribution and chemical composition of colloids in the ground water. Standard methods (e.g. light scattering) can be applied for high concentrations and large sizes of particles. Colloids smaller than 50 nm, however, are detected with very low efficiency. Laser induced breakdown detection (LIBD) can fill this gap. A new instrumentation is presented, which as compared to previous instruments, opens up a much wider operational dynamic range, now covering three orders of magnitude in size (5–1000 nm) and seven orders of magnitude in particle concentration (1 ppt – several ppm). The technique is based on plasma formation on colloidal particles inside the focus of a pulsed laser. The plasma plume is detected by three-dimensional optical observations and by means of its shock wave with a piezo-detector. For mathematical modelling, detailed knowledge on the photon fluence distribution in the focal region is indispensable. For the first time a true Gaussian TEM00 mode has been achieved in the focus of a LIBD apparatus and great care has been taken to guarantee long-term stability of the optical parameters. Automated control of the laser pulse energy and beam shape is introduced to allow routine reproducible measurement. The apparatus combines acoustic detection with three-dimensional optical monitoring of the focal region with two CCD cameras placed perpendicular to each other in order to gain additional size information. The breakdown events are systematically characterized with respect to the number density and size of aquatic colloids as a function of the laser pulse energy. Whereas the threshold energy (irradiance) only depends on the colloid size, the breakdown probability at higher pulse energies is a direct function of the number density of colloids. A correlation of the two facts allows the speciation of the colloidal size distribution.