Nuclepore

Fig. 27. Scanning electron micrograph (a) and cross-sectional comparison (b) of screen and depth filters both having a nominal particulate cut-off of 0.4 flm. The screen filter (a Nuclepore radiation track membrane) captures particulates at the surface. The phase-inversion ceUulosic membrane traps the...

These effects were enhanced in a modification (44) in which a set of many more and smaller schlieren apertures is prepared by placing a Nuclepore filter with 8-p.m pores on a coversHp and evaporating a metal onto the filter, perpendicular to it. The metal then coats and renders opaque the top of the... 

After the stipulated leaching period, the waters were sampled before and after filtration through 0.05 ym Nuclepore filters and the oxidation-state distribution of plutonium in the filtrates was determined as follows PrF3 carrier precipitation for Pu(III) and (IV), PrF3 precipitation following NaHS03 reduction for total plutonium, and thenoyltrifluoroacetone (TTA) extraction... 

With a syringe and firm pressure, pass 5 to 7 ml of blood through a 5-/rm Nuclepore filter held in a Swinney adapter. 

The spectral ratios (S.R.) given in Tables II and III show that Nuclepore filters and copper discs have the highest S.R., indicating that less degradation of the spectra, and hence, highest energy resolution, occurs. It should be noted, that except for cotton cloth (Table II), there seems to be a correlation between the S.R. and the activity plated-out on the material. 

While nuclepore polycarbonate membranes (0.4 ]im) were preferred as backup filters when sulfate was to be measured, glass-fiber filters had to be used in the HVI measurements. 

Adsorption Isotherms. The adsorption isotherms were determined using the serum-replacement adsorption or desorption methods (7). For the adsorption method, the latex samples (50 or 100 cm 2% solids) containing varying amounts of PVA were equilibrated for 36 hours at 25°C, placed in the serum replacement cell equipped with a Nuclepore membrane of the appropriate pore size, and pressurized to separate a small sample of the serum from the latex. For the desorption method, the latex samples (250 cm 2.5% solids) were equilibrated for 36 hours at 25°C and subjected to serum replacement with DDI water at a constant 9-10 cm /hour. The exit stream was monitored using a differential refractometer. The mean residence time of the feed stream was ca. 25 hours. It was assumed that equilibrium between the adsorbed and solute PVA was maintained throughout the serum replacement. For both methods, the PVA concentration was determined using a An-C calibration curve. 

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 [43]. After about 24 h, the samples were filtered on 0.4 jtm Nuclepore filters. The separated precipitates were dissolved with hydrochloric acid and the solutions 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 AAS (EAAS). The decomposition of organic complexes and other procedures were also examined by EAAS. 

Pores with a very regular, linear shape can be produced by the track-etch method (Quinn et al. 1972). Here a thin layer of a material is bombarded with highly energetic particles from a radioactive source. The track left behind in the material is much more sensitive to an etchant in the direction of the track axis than perpendicular to it. So etching the material results in straight pores of uniform shape and size with pore diameters ranging between 6 nm and 1200 nm. To avoid overlap of pores only 2-5% of the surface can be occupied by the pores. This process has been applied on polymers (e.g. Nuclepore membranes) and on some inorganic systems like mica. Membranes so obtained are attractive as model systems for fundamental studies. 

The extruder (Northern Lipids) is assembled with two polycarbonate filters (Nuclepore polycarbonate membranes Whatman) with pore size of 0.1 pm and diameter of 25 mM, and connected to a circulating water bath equilibrated at 65°C. The lipid emulsion is extruded 10 times through the filters under a pressure of approximately 400 psi. For larger LUVs (200-400 nm), lower pressures will be adequate (100-200 psi). After each pass, the sample is cycled back to the extruder. It is important to start at a low pressure and gradually increase until each pass takes less than one minute. 

Figure 1. Cross-section of Type A asymmetric UF membrane from a Nuclepore...

Figure 19. Nuclepore Type A UF hollow-fiber showing the direction of flow...

Figure 21. Nuclepore hollow-fiber module end potting...

Prior to joining Beckman Coulter, he served in several technical management roles including R D director at BioProbe International, R D director at Costar-Nuclepore, and R D group leader, chemistry, at BioRad Laboratories. 

The Nuclepore membranes used for this work were standard polyester membranes 25 mm in diameter. The pore number, N, is calculated from the pore density and the effective flowing area of... 

The fine particle airstream from the cyclone was sampled by two total filters in parallel. A Millipore Fluoropore 47 mm diameter Teflon filter with a 1 pm pore size was used for the first seven samples. Subsequent samples were obtained with a 0.4 pm pore size 47 mm Nuclepore polycarbonate filter because particle absorption measurements and elemental analysis by particle induced X-ray emission (PIXE) were easier and more accurate using the Nuclepore filters. In parallel with the Nuclepore filter, a TWOMASS tape sampler collected aerosol using a Pallflex Tissuequartz tape. The aerosol deposit area was 9.62 cm on the Nuclepore and Millipore filters and 0.317 cm on the Tissuequartz tape. The flow rate was 16-20 1pm through the Nuclepore and Millipore filters and 10 1pm through the Tissuequartz tape. Each Millipore or Nuclepore filter was placed in a labeled plastic container immediately after collected, sealed with Parafilm, enclosed in a ziplock bag, and placed in a refrigerator in the trailer. The tape in the TWOMASS sampler was advanced between samples. The tape sample was removed about once every 8-10 weeks and stored similarly to the Nuclepore filters. The TWOMASS was cleaned at that time. All samples were stored in an ice chest during the return trip to Caltech. Field blanks were handled identically to the samples. Of approximately 100 filter samples collected in 1979, 61 were selected for analysis. The 61 were chosen to span the variation in bjp and to obtain representative seasonal and diurnal samples. Sample times varied from 6 to 72 hours, with an average of 20.1 hours. 

The aerosol mass on each Nuclepore filter sample was determined gravimetrically. Field blanks were obtained at Zilnez Mesa by drawing 50 X. of filtered air through preweighed Nuclepore... 

Elemental mass concentration - One-third of each Nuclepore filter was sent to Crocker Nuclear Laboratory, University of California, Davis, for elemental analysis by particle induced X-ray emission (PIXE)(14). Masses of many elements from A1 to Pb were determined with this technique, including Si, S, K, Ca,... 

SOZ, NO3, NH4 mass concentration - One-half of each Nuclepore filter was analyzed by Environmental Research and Technology, Inc. (ERT), Westlake Village, California. Their laboratory determined the masses of aerosol sulfate and nitrate on each filter by liquid ion chromatography and ammonium by colorimetry. Based on duplicate analysis of samples and standards the uncertainty in the various determinations per filter were ... 

Filter substrates were chosen that were suited for subsequent determinations of aerosol mass, total carbon, elemental carbon, trace metals and aerosol light absorption coefficient The three filter assemblies contained, a 47 mm Pallflex Tissuquartz filter (2500 QAO), a 47 mm Nuclepore polycarbonate filter (0.40 ym pore size) and a 13 mm Pallflex Tissuquartz filter (2500 QAO). 

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