Nuclepore Membrane Filter Research Articles

PIXE analysis of heavy metals in water samples from a mining area in Mongolia

The affect of mining activity on the environment has been long of public concern. The present paper deals with chemical analysis of the Boroo River water samples collected in mining area of Mongolia focusing the determination of heavy metal contents by particle induced X-ray emission (PIXE) technique. The samples were prepared by preconcentration method (water samples treated to form metal–dibenzyldithiocarbamate (DBDTC) complexes and collected on a nuclepore track-etch membrane filter) and irradiated by 2.5MeV proton beam from the single-end type Van de Graaff accelerator. The accuracy of the results was proved by using certified river water samples. The total dispersions of experimental procedure were evaluated by variance analysis.

Pore Size Distribution Measurements of Nonwoven Fibrous Filter by Differential Flow Method

The differential flow method (DFM) test equipment was newly developed to measure the pore size distribution (PSD) of filter having relatively large pore size like nonwoven fibrous filter. The applicability of this equipment was investigated by using the Nuclepore membrane filters (PC membranes) having different pore size of 0.4, 0.8, 1.2 and 2.0μm and the stainless steel nonwoven fibrous filter having different fiber diameter and filter porosity. The fiber diameters of stainless steel were 2, 4 and 8μm and the range of filter porosity was 0.6-0.85. The PSD of PC membranes measured by DFM almost agreed with that measured by SEM observation and the mean flow pore size measured by DFM also agreed with the nominal one. The PSD was not influenced by the kind of wetting liquids used here, i.e. ethylene glycol, IPA and PorofilTM. The PSD of nonwoven fibrous filter depended on the kind of wetting liquids, although the maximum pore size evaluated by the bubble point was not influenced by them. The mean flow pore size measured by DFM in the nonwoven fibrous filter almost agreed with the mean pore size measured by liquid permeation method.

Comparison of different types of filters for atmospheric trace element analysis by three analytical methods

Different atmospheric aerosol samples were collected on three types of filters. From both of the loaded and clean areas of each kind of filter, different disks were cut and investigated by XRF, PIXE and scanning electron microscopy (SEM). The blank concentration values of the elements Al, Si, P, S, Cl, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Br and Pb in the three types of filter are discussed. It is found that for trace elemental analysis, the Nuclepore membrane filters are the most suitable for sampling. These filters have much lower blank element concentrations than the glass fiber and ash free filters. It was found also that PIXE is a more reliable analytical technique for atmospheric aerosol particles than the other methods used.

Photometric application of the Gram stain method to characterize natural bacterial populations in aquatic environments.

The Gram stain method was applied to the photometric characterization of aquatic bacterial populations with a charge-coupled device camera and an image analyzer. Escherichia coli and Bacillus subtilis were used as standards of typical gram-negative and gram-positive bacteria, respectively. A mounting agent to obtain clear images of Gram-stained bacteria on Nuclepore membrane filters was developed. The bacterial stainability by the Gram stain was indicated by the Gram stain index (GSI), which was applicable not only to the dichotomous classification of bacteria but also to the characterization of cell wall structure. The GSI spectra of natural bacterial populations in water with various levels of eutrophication showed a distinct profile, suggesting possible staining specificity that indicates the presence of a particular bacterial population in the aquatic environment.

A porous carbon film for the collection of atmospheric aerosol for transmission electron microscopy

This paper describes a method of direct sampling of fine urban aerosol using porous carbon films, to increase collection efficiency and retain the structural integrity of the aerosol. A nuclepore membrane filter was coated with carbon and washed with chloroform to leave a clean porous carbon film on a 200‐mesh transmission electron microscope copper grid. The grid was attached to a clean nuclepore filter using carbon cement. Sampling was conducted for 1 h at 1.9 L min−1 flow rate. The porous carbon grid with sample was then assayed using transmission electron microscopy, and negatives were suitable for image analysis. The collection of fine airborne particles using this method is appropriate for electron microscopy, with a minimum of interference to the structure of collected particles.

Investigation of different types of filters for atmospheric trace elements analysis by three analytical techniques

Different atmospheric aerosol samples were collected on three types of filters. Disks of both loaded and clean areas of each kind of filter were investigated by XRF, PIXE and Scanning Electron Microscope (SEM) methods. The blank concentration values of the elements Al, Si, P, S, Cl, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Br and Pb in the three types of fiters are discussed. It is found that for trace elemental analysis, the Nuclepore membrane filters are the most suitable for sampling. These have much lower blank element concentration values than the glass fibres and ash free filters. It was found also that the PIXE method is a more reliable analytical technique for atmospheric aerosol particles than the other methods.

Preconcentration of trace heavy metals in water by coprecipitation with magnesium oxinate for electrothermal atomic absorption spectrometry

Nanogram quantities of heavy metals in 200 ml of water were quantitatively preconcentrated by coprecipitation with magnesium oxinate at pH 9–9.5. The precipitate was collected on a 1-μm Nuclepore membrane filter and then dissolved in 5 ml of 1 mol/l nitric acid. After diluting to 10 ml with water, a 10- or 20-μl aliquot of the solution was directly analyzed by electrothermal atomic absorption spectrometry using deuterium background correction. The background absorption due to the collector magnesium oxinate was negligibly small. The optimized coprecipitation technique has been applied to the determination of cobalt, nickel, copper, cadmium and lead at the ppt level in river and seawater. The relative standard deviations were within 10% and the detection limits were 0.025 (for Co), 0.019 (for Ni), 0.006 (for Cu), 0.001 (for Cd) and 0.017 μg/l (for Pb). Blanks through the whole procedure were not detectable.

The preparation of ambient aerosol filter candidate reference materials for elemental analysis

Aerosol reference materials available today are discussed with respect to the requirements of X-ray analytical techniques. The lack of a proper reference material for this purpose, which would consist of real aerosol collected onto filter membranes, has to be ascertained. An aerosol sampling procedure is described, providing homogeneous aerosol deposits on filters large enough to be subdivided into filter pieces which could serve as units of a prospective reference material. The elemental uniformity of the dust deposits, assessed down to typical beam spot sizes of PIXE analysis, renders certification of such aerosol filters for elemental analysis feasible. An aerosol collection campaign has been started aiming at the production of candidate reference materials of three different aerosol matrices (urban, rural and marine) on cellulose nitrate and Nuclepore membrane filters.

Sources and composition of aerosol from Khartoum, Sudan

Aerosol sampling was carried out during December 1989 in Khartoum, Sudan, using Nuclepore membrane filters. Twenty-four aerosol samples were collected and analysed by X-ray fluorescence (XRF) spectrometry and particle-induced X-ray emission (PIXE). In addition, individual particle analysis was also performed on 19 samples using electron probe X-ray microanalysis (EPXMA). Good agreement between XRF and PIXE results was obtained for most of the elements. Enrichment factor calculations indicated that soil dispersion is the dominant source for most elements in the aerosol. However, certain elements showed high enrichment factors indicating the presence of anthropogenic sources. From a comparison with available literature data it appeared that the enrichment factors for the enriched elements in the Khartoum aerosol are among the lowest recorded values for urban aerosol. Absolute principal components analysis (APCA) was performed on the data and confirmed the findings from the enrichment factor calculations, i.e. a dominant soil dispersion source and an anthropogenic source for some of the elements. Because of the very limited number of impotant aerosol sources, the data set was reporduced by the APCA model with a reasonable degree of success. Single particle analysis also showed that most of the particles were soil dust. These particles could further be differentiated into alumino-silicates, quartz and CaCO 3 particles. Some of the particles were found to originate from combustion sources. EPXMA gave clues to the process of formation for some of the particles from combustion sources.

Studies on the mechanisms of active ion fluxes across alveolar epithelial cell monolayers

To investigate the cell physiologic and biological properties of the alveolar epithelium, we studied rat alveolar epithelial cell monolayers grown on permeable supports in primary culture. Type II alveolar epithelial cells were disaggregated using elastase, and partially purified on a discontinuous metrizamide gradient. These isolated cells were plated onto tissue culture-treated Nuclepore membrane filters at 1.5×106 cells/cm2 and maintained in a humidified incubator (5% CO2 in air, 37° C). After 2 days in culture, the bathing media on both sides of the cell monolayers were changed to fresh culture medium, thus removing nonadherent cells (mostly leukocytes). These monolayers exhibit a high transmonolayer resistance (>2000 Ω-cm2) and actively transport ions. Radionuclide flux studies indicate that Na+ is the predominant ionic species absorbed actively under baseline conditions, accounting for about 80% of the total active ion transport. Cl− seems to be passively transported across the epithelium. However, when the epithelium is exposed to a beta-agonist (terbutaline), active absorption of Na+ is increased and active absorption of Cl− occurs. Although it is clear that both active Na+ and Cl− transport are dependent on Na+/K+-ATPase activity, and that Na+ enters cells predominantly through channels, the specific mechanisms by which Cl− enters and exits the alveolar epithelial cells remain unclear. The stimulated reabsorption of Na+ and Cl− may be important in helping to remove excess fluid from alveolar air spaces in the lung.

Collection Efficiency of the Nuclepore Membrane Filter for Aerosol Sampling and Its Application to 218Po Measurement

An α spectrometry combined with a filter sampling method has been applied for the measurement of radioactive aerosols. The Nuclepore membrane filter was used for the aerosol sampling, and its collection efficiency was experimentally determined. Examples of measured 218Po concentrations in three rooms were given.

Properties of isolated extrachromosomal nucleoli from Tetrahymena pyriformis.

Extrachromosomal nucleoli were isolated from log phase cells of Tetrahymena pyriformis (amicronucleate strain) in a highly purified state. Nucleoli located at the periphery of the macronucleus were detached from the nucleoplasmic mass of isolated macronuclei with agitation and separated from macronuclei by filtration through a Nuclepore membrane filter (pore size 5 microm). The filtrate constitutes the crude nucleolar preparation, as judged by electron microscopy and DNA analysis. Further purification of the nucleoli was performed by isopycnic centrifugation of the filtrate in a Metrizamide density gradient. After this step, the purity of the nucleoli, as defined by rDNA content and measured by analytical CsCl centrifugation, was almost 100%. Electron microscopy of the purified nucleoli revealed structures that resemble those of an in situ nucleoli. Undegraded 35S pre-rRNA, together with 26S and 17S rRNA, could be isolated from purified nucleoli. In vitro RNA synthetic activity was associated with isolated nucleoli. This activity is insensitive to low and high concentrations of alpha-amanitin, indicating that the form I RNA polymerase is functioning.

Minimization of the Amount of Indium Carrier in Coprecipitation for the Determination of Cadmium by Graphite-Furnace Atomic Absorption Spectrometry

Nanogram quantities of cadmium in 100 ml of water are quantitatively (»precipitated with indium hydroxide (100 μg as indium) at pH 9.5. The precipitate is separated from the mother liquor by filtration with a 1-μn Nuclepore membrane filter and ultrasonically dissolved in 1 M nitric acid. The cadmium in the final solution (1 ml) is directly determined by graphite-furnace atomic absorption spectrometry without any serious background absorption due to indium. For the analysis of river water, coprecipitation is combined with sorption on a Sephadex A-25 anion exchanger for the separation of humic substances. The proposed method allows discrimination between negatively and positively charged cadmium species, with a detection limit as small as 2 ngCd I-1 of water.

Contact sensing in Candida albicans: a possible aid to epithelial penetration.

Hyphal development in the dimorphic pathogenic fungus Candida albicans is thought to facilitate the primary invasion of surface epithelia during superficial infections. When mycelia were grown on Nuclepore membrane filters that were placed over serum-containing agar, the hyphae grew over the membrane surface and through the pores thereby crossing to the other side of the membrane. Hyphae that did not contact the lip of a pore did not enter it. The response was likely to be due to contact guidance (thigmotropism) and not chemotropism towards the nutrients since hyphae growing on the underside of the membrane also entered the pores then grew away from the underlying nutrient agar. The response therefore seems to be due to sensation of the substrate topography, and tropic movement in relation to changes in contour. This behaviour may enable the hyphae to penetrate epithelia at microscopic wound sites, membrane invaginations and other foci where the integrity of the epithelium is weak.

Time-dependent charge in a dielectric membrane filter

Problems with electrostatic charge that appear when dealing with Nuclepore membrane filters in aerosol sampling are discussed. A simple method to measure directly the electric charge in a membrane is presented and applied to measure the charge of a Nuclepore filter during the filtration process and other situations. Results of measurements of the charge collected by the filter in the course of a normal atmospheric filtration operation are shown. Asymptotic charges as large as 4 nC, depending on relative humidity, were observed. Additional electrostatic effects due to filter manipulation and holding are also measured. Next, the loss rate of charge transferred by friction to the filter is evaluated, and a parametric equation for the charge as a function of time is proposed and fitted to the experimental data. This equation is composed of two exponential functions, representing fast and slow decay of charge. Furthermore, the charge decay of the filter was strongly affected by the presence of an ionizing radiative source. The decay parameters are used to determine a general formula describing the accumulation of charge during filtration. The electric charge in the filter may be studied as two different species: surface charges and bulk charges. Their time dependency is explained by a growth term and a loss term. The need to consider the electric charge in Nuclepore filters for a correct determination of the mass of the sample and for evaluation of filter efficiency in quantitative analysis, is discussed.

Calculation of the theoretical response of an optical particle counter and its practical usefulness

The response of an optical particle counter (OPC) was modelled from the Mie theory of light scattering and the built-in parameters of the counter. The model allowed the calculation of the output signal for any spherical particle, of a given complex refractive index, on a microcomputer. It was applied to a Royco 225 instrument. The simulation required a calibration with a reference aerosol. This calibration was carried out with monodisperse spherical particles of oleic acid obtained by a vibrating orifice aerosol generator (VOAG). The experimental values of the counter response obtained with monodisperse aerosols of oleic acid and methylene blue were then compared with the results obtained from the model. It was shown that the choice of the material used for generating monodisperse particles in order to calibrate the counter was not important. Particle size distributions were measured by the OPC for two polydisperse aerosols (coal and aluminium oxide particles), by using the response curve predicted from the model and the refractive index of the material, and then compared with those measured using a Coulter counter, after aerosol sampling onto a Nuclepore membrane filter. The comparison shows that the combination of optical measurements with the calculation of the response curve of the OPC yields accurate results when particle shape is close to the sphere, and for nonspherical particles when light absorption is high.

Inorganic chemical approaches to pharmacognosy. VIII. Determination of selenium in crude drugs by energy-dispersive X-ray fluorescence spectrometry.

Energy-dispersive X-ray fluorescence spectrometry following sample decomposition and preconcentration was developed to determine selenium in crude drugs. Samples were decomposed with conc. HNO3 and conc. H2SO4 in a flask with a reflux condenser. Evaporation of HNO3 had to be avoided to prevent serious loss of this element. Selenium was preconcentrated from the digestion liquid by two-step reduction with 4M HCl and ascorbic acid, the elemental selenium formed was adsorbed on activated carbon and then collected on a Nuclepore membrane filter for direct irradiation in an X-ray spectrometer. This analytical method (detection limit, 0.03 ppm) was used to determine selenium in many kinds of crude drugs. The analytical results indicated vegetable drugs to be low in selenium content: more than 0.5 ppm in only a limited number of samples and less than detection limit (0.03 ppm) in nearly all the samples. Animal drugs contain selenium at higher levels, Lumbricus and Cantharis being 7.46 and 1.67 ppm, respectively.

Calcutta Pollutants: Part III. Toxic Metals in Dust and Characterisation of Individual Aerosol Particles

Abstract The concentration of eight heavy metals Cr, Mn, Co, Ni, Cu, Zn, Cd and Pb on dust of street, household, restaurant, top of leaves and five soil samples of Calcutta city are measured by Atomic Absorption Spectrometry (AAS) and Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). The available metals of dust samples in 0.07 N (HCl) are also measured by AAS. The Electron Probe Micro Analysis (EPMA) is also made to characterize individual aerosol particles collected on Nuclepore membrane filter.

Precise X-ray production cross-section measurements of medium Z elements by protons

The K a X-ray production cross sections of 53I, 55Cs, 56Ba and 57La for protons between 1.5 MeV and 3.0 MeV have been measured. Moreover, the K-shell ionization cross sections of 29Cu and 35 Br are reported. The targets are in the form of thin layers mounted on three different types of backings: nuclepore membrane filter, mylar, and thin carbon foil. The experimental results are compared with the most recent formulations of the perturbed stationary state model corrected for Coulomb deflection, relativistic and energy loss effects (ECPSSR), and of the relativistic plane wave Born approximation corrected for binding effect and Coulomb deflection (RPWBA-BC).

Conjunction of PIXE with the inertial spectrometer aerosol sampler to permit quantitative, contiguous, narrow resolution particle size measurement

We have developed a protocol using PIXE analysis whereby aerosol samples collected by an inertial spectrometer sampler can be simultaneously characterized for elemental concentration and aerodynamic particle size. Quantitative collection and analysis of ambient aerosols over a wide aerodynamic size range is possible, with an average of 0.08 μ mad size fractionation resolution. The inertial spectrometer sampler has a throat whose sides converge to a rectangular channel which bends through 90°. Clean air is drawn through the throat, and a thin ambient aerosol sheath is injected in front of the channel close to the inner wall of the throat. The surface past the bend consists of a Nuclepore membrane filter through which the air is drawn. Because of their curved path through the bend, the particles are separated according to their size and this separation is magnified by projection onto the filter. Exposed Nuclepore is analysed by PIXE in a He filled chamber. A pulsed proton beam from a Tandetron accelerator is homogenized by an X − Y sweep and collimated to 0.5 mm width using carbon slits. Nuclepore targets are placed at 45° and tracked in 0.9 mm steps across the beam using a directly coupled stepping motor. Position corresponds to particle size. Approximately 2 μC charge is collected at 1.58 MeV and 30 μC at 2.52 MeV with a polystyrene absorber at a 2 μA cm −2 beam current. The distribution of elemental concentrations with aerosol particle size for an urban indoor air samples is measured and the detail observed is demonstrated in examples given of calcium and iron concentrations obtained by 33 approximate 0.08 μ mad “steps” across a ≤ 0.30 μ mad- ≥ 8.0 μ mad particle size range. The sampling method may be extended into the sub-micrometer size range, further enhancing analytical versatility. Because of the sampling simplicity and the resolution and accuracy of analysis, this method can have widespread application.