Nuclepore® filter

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. 

A second way to achieve collection of coarse- and fine-mode particles onto filters is through tandem filtration through the stacked filter unit (SFU) (4, 5, 6). In these devices, the convenient filtration characteristics of filters (Nuclepore) allow a 2.5- xm cut point on the basis of pore size and the face velocity of the airstream. Such devices are very compact and inexpensive and have been heavily used in remote-area networks (7, 8, 9). Again, however, the limitations of the method limit the number and sharpness of the size cuts so that almost all units are operated at 2.5 xm and give coarse and fine fractions very much like those of the virtual impactor. Examples of the 2.5- xm cut points of VI, SFU, and impactors are shown in Figure 2. However, cyclones, virtual impactors, and stacked filter units cannot give the sharp, multiple cut points of impactors as shown in Figure 1. 

A Teflon-coated sampler (General Oceanics, 10-L Go-Flo) on a stainless steel hydrowire was used to obtain whole-water samples and samples for filtration from 16 points in the water column on each cruise. Samples were pressure filtered onboard ship, within a Class-100 laminar flow enclosure, in an all-Teflon column-filter holder (Savilex) through tared 0.4-pm track-etched filters (Nuclepore). Samples, both total P and total filtrable P, were acidified with high-purity HC1 (Ultrex) and immediately frozen. 

Filtration (12) of whole lake water from niskin casts and centrifugate from continuous-flow centrifuges was accomplished with track-etched filters (Nuclepore) of various pore sizes. For P, the fractionation protocol employed filters rated at 1.0, 0.4,... 

Membrane filter (Nuclepore Corp.) pore diameter 5-10 pm, pore density 4 x 105 pores/cm2. 

Pass the suspension though a stacked pair of polycarbonate 100-nm filters (Nuclepore) using an extruder. The suspension should be allowed to equilibrate for 5 min inside the extruder before pressure is applied in cases where the extrusion is performed above room temperature. 

Filters Nuclepore polycarbonate filters (Nuclepore,Track-GTCN Membrane, Whatman cat no. 110 GOS). The pore size routinely used is 0.1 pm (see Note 4). The filters are cut in half, washed in detergent, rinsed under running water for 2h and 10°— in distilled water, and stored in 70% ethanol... 

Displacement of the separated polymers from the tube through the detectors was accomplished by injecting a dense fluorocarbon chase solution into the bottom of the tube by means of a syringe pump. The chase solution displaced the tube contents upward out of the top of the tube through a filter (Nuclepore or Millipore), a flow-through UV detector, and finally, the LALLS detector. 

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. 

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. 

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). 

In a search for sources of alkaline materials in rural air and rain, we have sampled and performed multi-element analyses on ambient particulate matter and potential source materials. Ambient aerosols were sampled daily using single Nuclepore filters or Florida State University "streakers." Samples of soil and unpaved road materials were also collected and analyzed. The samples were analyzed by various multi-element methods, including ion-and proton-induced X-ray emission and X-ray fluorescence, as well as by atomic absorption spectrophotometry. Visual observations, as well as airborne elemental concentration distributions with wind direction and elemental abundances in aerosols and source materials, suggested that soil and road dust both contribute to airborne Ca. Factor analysis was able to identify only a "crustal" source, but a simple mass balance suggested that roads are the major source of Ca in rural central Illinois in summer. 

---