Nucleopore filter

For aqueous samples, time and temperature studies report that, at higher concentrations (0.27 p M), immediate storage of filtered [0.45 pm polycarbonate filters (nucleopore)] and acidified [to 1% with HC1 (supra-pure)] natural waters at about 5°C can preserve As(III) and As(V) concentrations for about 30 days.57 It is advisable that samples with lower As concentrations be kept in the dark at 4°C.58... 

Multilamellar liposomes were prepared by standard methods (6), and prior to incorporation into the delivery systems, were passed through a 0.8 pm filter (Nucleopore, Pleasanton, CA) to remove very large structures and/or aggregates. 

With the use of a quartz filter in front of the PUF22 the possible presence of dust in the test chambers was investigated. 50 m chamber air were sucked through the filter. The filter was weighed before and after under the same climate conditions and no dust was found gravimetrically. Even on a special gold-plated filter (nucleopore) which is normally used for determination of asbestos in air there was no detection of dust particles with an electron microscope. 

PUF22 Quartz filter Nucleopore filter Sum PUF13... 

The suspending media employed were isotonic saline containing 0.05% w/v of formalin distilled water isopropyl alcohol 5% w/v NH4SCN in isopropyl alcohol. All suspending media were filtered using 0.8 pm and subsequently 0.45 pm MF filters (MILLIPORE CORP., USA-Bedford,MASS.) for aqueous media and 0.8-0.4 pm polycarbonate filters (Nucleopore, USA-Pleasanton, CA.) for organic media. 

Freeing a solution from extremely small particles [e.g. for optical rotatory dispersion (ORD) or circular dichroism (CD) measurements] requires filters with very small pore size. Commercially available (Millipore, Gelman, Nucleopore) filters other than cellulose or glass include nylon, Teflon, and polyvinyl chloride, and the pore diameter may be as small as 0.01 micron (see Table 6). Special containers are used to hold the filters, through which the solution is pressed by applying pressure, e.g. from a syringe. Some of these filters can be used to clear strong sulfuric acid solutions. 

Air (particulate and organolead) Collection of particulate matter collected onto nucleopore filters filtered gases cryogenically trapped and thermally desorbed XRF (particulate) GC/GFAAS (gaseous) 0.3 pg/m3 0.2 ng/m3 46->90 90-100 De Jonghe et al. 19 ... 

Cranston and Murray [171,188] took the samples in polyethylene bottles that had been precleaned at 20 °C for 4 days with 1% distilled hydrochloric acid. Total chromium (CrVI) + Cr111 + Crp (particulate chromium) was coprecipitated with iron (II) hydroxide, and reduced chromium (Cr111 + Crp) was coprecipitated with iron (III) hydroxide. These coprecipitation steps were completed within minutes of sample collection to minimise storage problems. The iron hydroxide precipitates were filtered through 0.4 pm nucleopore filters and stored... 

The collection behaviour of chromium species was examined as follows. Seawater (400 ml) spiked with 10-8 M Crm, CrVI, and Crm organic complexes labelled with 51Cr was adjusted to the desired pH by hydrochloric acid or sodium hydroxide. An appropriate amount of hydrated iron (III) or bismuth oxide was added the oxide precipitates were prepared separately and washed thoroughly with distilled water before use [200]. After about 24 h, the samples were filtered on 0.4 pm nucleopore filters. The separated precipitates were dissolved with hydrochloric acid, and the solutions thus obtained were used for /-activity measurements. In the examination of solvent extraction, chromium was measured by using 51Cr, while iron and bismuth were measured by electrothermal atomic absorption spectrometry. The decomposition of organic complexes and other procedures were also examined by electrothermal atomic absorption spectrometry. 

An aliquot of the diatom sample is brought down onto a Nucleopore filter (2.0 pm pore size will work for most diatoms) using a hand pump or light vacuum filter system. 

Figure 2. Membrane-separated culture apparatus, modified for anaerobic operation, M, nucleopore membrane O, overflow S, magnetic stirrers E, extension tubes F, millipore filters.

Millipore filters have twisted, interconnecting pores that are much more complex than those in Nucleopore filters. They are available in different materials such as Teflon, polycarbonate, quartz, silver, and cellulose acetate. 

Atomospheric deposition (snow) determination in soluble (chromium(VI)) and particulate (chromium(lll)) part The melted snow filtered through Nucleopore filter the filtrate acidified with HN03 and dried by freeze-drier residue dissolved in HN03 this preconcentrated solution placed in plastic tubes both plastic tube and Nuclepore filter irradiated with protons PIXE 2 pg/L (soluble portion) 26 pg/L (snow particle) No data Jervis et al. 1983 Landsberger et al. 1983... 

Multi-well modified Boyden chambers can be obtained from Neuro Probe Inc. (Gaithersburg, MD). Model AP48 has been widely used for endothelial cell chemotaxis assays. The apparatus consists of top and bottom acrylic plates, a silicon gasket and assembly screws. The bottom plate has 48 wells, each with 25 pL final volume. These correspond to holes on the top plate, and form the upper wells when the chamber is assembled. The filter (polycarbonate, 25 x 80 mm) is placed between the top and bottom plates, and a gasket is placed over the filter to create the seal. The apparatus can be purchased with a selection of accessories, such as curved forceps, filter clamps, and wipers. These are required to process the filters after use. Filters can also be obtained from Nucleopore Inc. (Pleasanton, CA) and Costar (Cambridge, MA). 

Soot samples were obtained by use of a nitrogen-quench, porous-walled probe and Nucleopore filters (7). Gas phase hydrocarbons were collected by the porous probe as batch samples and analyzed by standard FID gas chromatography. Thermal measurements included gas temperature by radiation-corrected bare wire thermocouple, and soot temperature by Kurlbaum reversal (9, 10) and two color pyrometry (11). 

After exposure of cells to radiation or oxidant treatment, between (2-4) x 105 cells are loaded at 40°C onto a Nucleopore 25 mm, 2 pm pore size, polycarbonate filter (Bio-Rad Laboratories) on a filter support. 

NBT (Sigma Chemical Co.) ninhydrin (Sigma Chemical Co.) nitric acid (70% spectrosil) (Merck) Nucleopore polycarbonate filter (Bio-Rad Laboratories) oxalic acid (Sigma Chemical Co.)... 

Lung tissue Dry to constant weight digest with sodium hyroxide (90 °C) ash residue collect on nucleopore filter TEM 0.1x10 f/g No data Wagner et al. 1982a... 

A 13-mm holder for Nucleopore filters equipped with a dual inlet valve (Nucleopore Co., Cambridge, MA) nucleopore filters, 13 mm, 10 /xm pore size fraction collector syringes (1 and 50 ml) ... 

Cell filterability is influenced by a variety of biological and technological factors (Nordt, 1983). Thus, in order to be reliable and reproducible, Nucleopore filtration techniques must fulfil certain criteria, and namely (1) the most part of the input cells must be recovered in the filtrate (2) cellular aggregation should be minimized by choosing conditions which permit relatively short filtration times (3) cell viability should be high and not lost on filtration (4) cell size distribution should not be influenced by filtration and (5) differences in cell to filter and cell to cell adhesion of different cell lines should not be responsible for differences in filterability. In order to fulfil these criteria, experimental parameters such as cell to pore ratio, filtration pressure and cell culmre conditions have to be standardized. The following optimal conditions have been established for filtration of B16 melanoma cells (mean cell diameter 17.4 0.21 /xm, mean diameter of cell nuclei 9.8 0.27/xm) 20 cm H2O driving pressure, cell-to-pore ratio 1 1, temperature 22°C (Ochalek et al., 1988). Care has to be taken to derive tumor cells from similar culture conditions, since cell density has been found to influence filterability. 

Nucleopore filters from the same lot should be used throughout the experiments. While pore diameter is uniform, there might be considerable variability in pore density. Therefore, filters should be checked before use by passing a certain amount of medium (20-50 ml), and measuring the time it takes to pass through this is proportional to the total pore area. Only filters giving similar flow values should be used in the experiments. 

Alternatively, measurement of cell filterability can be estimated by recording the passage time of cell suspensions at different concentrations, generating curves of filterability vs. cell concentration (Sato et al., 1977 Mittelman et al., 1994). The set up in this case consists of a Nucleopore filter holder which is loaded with the cell suspension, and to which a constant positive pressure (between 5 and 24 cm H2O) is applied (Fig. 3.6B). Filterability is then defined as the ratio between the filtration rate of the cell suspension (Vc) and the filtration rate of the same volume of medium alone (Vm). Since the input volume for different cell suspensions is the same, then filterability is proportional to the filtration time of the cell suspension (tc) vs. medium alone (tm) ... 

Since the filtration rate through a Nucleopore filter is sensitive to the ratio cell diameter/pore diameter (Kikuchi, 1991), such ratio should be maintained constant when comparing different cell lines which differ in size. 

Sato, H., Khato, J., Sato, T. and Suzuki, M. (1977). Deformability and filterabil-ity of tumor cells through nucleopore filter, with reference to viabiltiy and metastatic spread. GANN 20, 3-11. 

TuUberg, K. E. and Burger, M. M. (1985). Selection of B16 melanoma cells with increased metastatic potential and low intercellular cohesion using nucleopore filters. Invasion Metastasis 5, 1-15. 

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