Colloidal Size Range Research Articles

Continuous, free-flow electrophoresis: A modified approach

Electrophoresis is an exceptionally effective method for separating small particles or large molecules in the colloidal size range, and is widely used in biological and clinical studies to separate cells, viruses, and large proteins. It has become the standard analytical tool for detecting the presence of these materials. Despite the success of electrophoresis in analytical and research applications, there has been much less success in using electrophoresis in preparative-scale applications to separate large quantities of materials. A new or modified concept is described that eliminates some of the most serious problems that have arisen in adopting electrophoresis for preparative-scale separations. The new concept uses a narrow-gap flow system between the electrodes and eliminates or greatly reduces problems with thermal convection. In addition, the narrow gap can be a convenient annular region between two cylindrical electrodes. The electric potential is applied across the annulus (or across the narrow flow channel) and the potential applied to the electrodes is reversed periodically. Between the reversals of the electric field, the inner electrode (or one side of the narrow flow gap) is rotated periodically in different directions. This periodic motion and alternating of the applied field displaces charged particles in the angular direction. The rate of displacement depends on the electrophoretic mobility of the particles.

Fluid Extraction and Circulation in the Proventriculus of the Banana Prawn Penaeus merguiensis de Man

The morphology and gastric armature of the proventriculus of Penaeus merguiensis closely resembles that of predominantly macrophagous decapods. Two modes of gastric mill operation were observed, chewing and compression. Gastric mill activity typically began with several ventral compressions of the ossicles above the lateral teeth. This was followed by a single anterior chewing movement of the median tooth in conjunction with a shearing medial movement of the lateral teeth. Morphological examination and observations of fluid movements within the proventriculus of live specimens have added to a previous model of proventricular circulation. Fluids are drawn ventrally from the cardiac stomach through two filters, of which the first is coarser than the second. The gaps between the setules of the filter setae in the secondary filter indicate that only particles in the colloidal size range or smaller can enter the digestive gland. Fluids are removed from the digestive gland and pulled anteriorly through fully enclosed passageways to return to the cardiac stomach. This action is the result of suction created behind the median tooth as it swings anteriorly during normal gastric mill activity. The return of fluid to the cardiac stomach completes the circulation of proventricular fluids and would allow enzymes from the digestive gland to begin food digestion soon after it has been ingested. The chitinous muscular stomach of crus

Centrifugal SPLITT fractionation: new technique for separation of colloidal particles

A centrifugal SPLITT fractionation system has been assembled for the purpose of extending the capabilities of gravitational SPLITT fractionation to materials in the colloidal size range and to particles of low density. The integrity and capabilities of the system are examined using polystyrene and other latex beads. Fractionation is illustrated using a mixture of latex beads of two different diameters, 0.60 and 1.05 μm. In addition, palladium particles in the size range 0.03-0.3 μm are separated into small and large particle size fractions with diameters below and above 0.15 μm, respectively. Continuous fractionation is then carried out for periods ranging from 7h to 3 days using a polydisperse poly(vinyl chloride) latex material (0.2-2 μm, cut at 1.1 and 0.7 μm) and a polydisperse nematic curvilinear align phase liquid crystal emulsion (1-10 μm, cut at 2.8 μm). Fractionations is verified by electron microscopy and by size analysis using sedimentation field-flow fractionation. Throughputs are the order of 0.5-1.0 g/h; guidelines are provided to expand this level significantly

FLUID EXTRACTION AND CIRCULATION IN THE PROVENTRICULUS OF THE BANANA PRAWN PENAEUS MERGUIENSIS DE MAN

The morphology and gastric armature of the proventriculus of Penaeus merguiensis closely resembles that of predominantly macrophagous decapods. Two modes of gastric mill operation were observed, chewing and compression. Gastric mill activity typically began with several ventral compressions of the ossicles above the lateral teeth. This was followed by a single anterior chewing movement of the median tooth in conjunction with a shearing medial movement of the lateral teeth. Morphological examination and observations of fluid movements within the proventriculus of live specimens have added to a previous model of proventricular circulation. Fluids are drawn ventrally from the cardiac stomach through two filters, of which the first is coarser than the second. The gaps between the setules of the filter setae in the secondary filter indicate that only particles in the colloidal size range or smaller can enter the digestive gland. Fluids are removed from the digestive gland and pulled anteriorly through fully enclosed passageways to return to the cardiac stomach. This action is the result of suction created behind the median tooth as it swings anteriorly during normal gastric mill activity. The return of fluid to the cardiac stomach completes the circulation of proventricular fluids and would allow enzymes from the digestive gland to begin food digestion soon after it has been ingested.

Colloid size distributions in ion implanted glass

Ion implantation of silver ions at 60 keV into silicate glass produces metallic colloids. Colloid growth during implantation as recorded by in situ changes in optical reflectivity. Post implant analyses indluded optical absorption, Rutherford backscattering and transmission electron microscopy. The optical data imply there is a range of colloid sizes and the details of colloid size as a function of depth are determined by the TEM measurements of thinned samples. The factors influencing the changes in the optical data with ion dose and the depth dependence of the colloid size distribution are discussed.

Preparation of monodisperse ellipsoidal polystyrene particles

A method is described for the preparation of monodisperse ellipsoidal particles of polystyrene in the colloidal size range. Monodisperse polystyrene particles were dispersed in a solution of polyvinyl alcohol. This dispersion was then allowed to form, by evaporation, a thin film of polyvinyl alcohol containing spherical polystyrene particles. Strips of this film were clamped into a metal frame, heated rapidly in an oil bath to 200°C and stretched to a predetermined extent in order to convert the spherical particles into ellipsoids; the film was then cooled. A wide range of axial ratios for a variety of initial particle sizes was obtained by this method.

The Role of Colloid Interactions in Solid-Liquid Separation

Forces between particles in water become especially important when the particles are in the colloidal size range (less than a few mm). To a first approximation inter-particle forces or colloid interactions are linearly dependent on particle size and they become stronger, relative to external forces, as particle size decreases. The separation of fine particles from water by processes such as coagulation, filtration and flotation can be crucially dependent on the manipulation of colloid interactions, usually to promote attachment of particles to each other or to surfaces. The most important types of colloid interaction are briefly discussed. These include van der Waals forces, electrical interaction, hydration forces, hydrophobic interaction and effects associated with adsorbed polymers, such as steric repulsion and polymer bridging. These are all short-range interactions, which have little influence on the transport of particles but which can have a major effect on collision efficiencies and on the adhesion between particles. Some examples of solid-liquid separation processes in which colloid interactions are important are given.

Fractionation and concentration of suspended particulate matter in natural waters

AbstractA scheme for the fractionation and concentration of suspended particulate matter (SPM) from natural waters has been tested. This scheme involves the sequential use of three fractionation techniques—sieving, continuous flow centrifugation and tangential flow filtration to collect gram amounts of SPM over the entire particulate and colloidal size range. The separation scheme is able to process large samples (ca. 1001), within reasonable times (ca. 1 day) and the apparatus is portable. Reproducibility and potential artifacts introducing during the fractionation and concentration of SPM, particularly when tangential flow filtration is used, are discussed. It has been shown that there is a systematic increase in the content of organic carbon, Mg, Ca, Na, K, Cu and Zn with decreasing particle size, highlighting the importance of the colloidal ( < 1 μm) fraction.

Filtration of colloidal melanin from sea water by planktonic tunicates

PELAGIC tunicates of the genus Oikopleura produce, live in and pump water through mucous structures termed 'houses'. Because these houses contain filters with submicrometre pores, oikopleurids have been proposed as important consumers of participate organic carbon (POC) in the sea1. We present new evidence that they also consume 'dissolved' organic carbon (DOC) in the colloidal size range down to about 0.2 μm in diameter. Such colloids are more abundant in the sea than previously believed2,3, and have an important role in the global flux of carbon. Oikopleurid tunicates have the potential to filter a significant fraction of the water mass every day1,4, and to repack much of the colloidal DOC into their houses, faecal pellets and bodies. Oikopleurids are also known prey for several fish species5–7. Thus, we speculate the oikopleurid tunicates to mediate a substantial energy flow, from DOC through a two-step 'food-chain', to fish of commercial interest, by-passing energy-consuming respiration by bacteria and small planktonic protozoa.

The distribution of colloidal aluminum and organic carbon in coastal and open ocean waters off Nova Scotia

Cross-flow filtration has been used to study the size distribution of aluminum and organic carbon in an operationally defined colloidal size range (10,000 MW-0.45 μm; ~1–10 nm-0.45 μm) in coastal and open ocean waters off Nova Scotia. Colloidal aluminum was consistently <5% of the “dissolved” (0.45 μm filtered) fraction by direct measure and 15% of “dissolved” Al by difference (0.45 μm filtered minus 1–10 nm filtered). Concentrations of Al measured in the colloidal fraction were high in the surface waters of the shelf, 0.44–0.55 nM (3–4% of “dissolved”), and decreased to levels of 0.09–0.15 nM (~ 1% of “dissolved”) in deeper waters. The open ocean vertical distribution of colloidal Al was similar to that on the shelf, with elevated concentrations in surface waters, 0.16–0.19 nM (~ 1% of “dissolved”), decreasing to 0.01–0.08 nM (<0.5% of “dissolved”) in deep waters. Colloidal organic carbon was ~ <10–15% of “dissolved” organic carbon; however, we recognize that our organic carbon measurements may be underestimated by our analytical method which employs UV-photooxidation. Laboratory experiments, using 234Th tracer and several surface water samples, showed an increasing percentage of colloidal thorium from open ocean to nearshore waters; 234Th tracer was always slightly greater than Al in the colloidal size fraction. The relationship between the apparent distribution coefficient (K′d) for metals and particle concentration (Cp) for oceanic waters has been examined. Model predictions show that, for most of the global ocean, K′d will be independent of Cp. This result is in agreement with oceanic and laboratory K'd values determined for aluminum.

Crossflow filtration of colloids from baltic sea water

Samples of Baltic Sea water were processed by glass fiber filtration followed by crossflow filtration, resulting in a particulate and colloidal fraction. Crossflow filtration provided necessary filtration rates without contributing interfering contaminants. It is suggested that photo-oxidation, as employed herein, did not completely oxidize colloidal organic matter, thus underestimated its concentration. Percentages of organic carbon and aliphatic hydrocarbons in the colloidal size range were calculated, but should be viewed as semi-quantitative values due to observed inaccuracies introduced by the analytical procedures of filtration and organic carbon analyses.

Polydispersity effects in the small-angle scattering of concentrated solutions of colloidal spheres

Calculations are presented of the intensity of radiation scattered by a polydisperse system of spherical particles at finite concentrations where interparticle interference of the scattered waves becomes important. The results apply to small-angle (x-ray and neutron) scattering and to light scattering of a solution of particles in the colloidal size range. Use is made of a closed expression for the scattering of a multicomponent mixture of hard spheres recently derived by one of us. The derivation is based on Baxter’s solution of the Percus–Yevick approximation for hard sphere fluids.

Survey of Some Canadian Lakes for the Presence of Ultrastructurally Discrete Particles in the Colloidal Size Range

Water samples from nine Canadian lakes were centrifuged and the pellets were analyzed by transmission electron microscopy. The pellets included small organisms, organic colloids, and clay particles. In almost all the samples, colloids were the major component revealed following thin-section analysis. When viewed at high magnification, much of each pellet consisted of morphologically discrete particles, some of which were readily categorized. Electron-opaque fibrils of colloidal size were frequently encountered (1) at different depths, (2) as a coating on the surface of algae and bacteria, (3) overlaying the sediments, (4) as an apparent adhesive between a variety of particles, and (5) as a component of froth at the water–air interface. They were common at all times and in lakes of various trophic levels and sizes. Key words: water, colloids, fibrils, lakes, electron microscopy

Preferential Localization of Radiolabeled Liposomes in Liver

Liposome formulations were studied to achieve an efficient entrapment procedure for the production of liposomes of 99mTc-pentetic acid. The entrapment efficiency was studied by separation of the product using column chromatography. The particle-size range of the prepared liposomes was evaluated using electron microscopy. Entrapment techniques and separation procedures led to a liposome preparation with particles in the colloidal size range (0.001–0.5 pm). Dramatic differences in the organ distribution of the liposome preparation in mice were pro-duced when different particle-size ranges were injected. Liposomes eluted in the first fraction after the void volume led to a maximum uptake by the liver and spleen 10 min after intravenous injection. Liposomes from pooled fractions provided less than half of the activity in the liver, as did the narrow size range liposome preparation.