Filters silver membrane

PRO-TEK Colorimetric Air Monitoring Badge System Polyvinyl chloride filter Silver membrane filter Silica gel tube... 

Pass air through silver membrane filter. Silver membrane filters/ optical density measurements No data NR EPA 1978... 

Large volumes of water often need to be processed to obtain sufficient quantities of aquatic humic substances filtration is the slowest step in this process. In a comparison of filter flow rates, Cranston and Buckley (1972) found filtering times for 47 mm (millimeter) diameter filters increased in this order glass-fiber filters < silver-membrane filters < organic-membrane filters (cellulose-acetate and cellulose-nitrate). They also report that substantial variation exists between different silver filters from the same manufacturer. This is caused by variation in permeability (number of pores per unit area), not pore size, and did not occur with the other filters studied. 

A Goldberg, W Higuchi. Improved method for diffusion coefficient determinations employing the silver membrane filter. J Pharm Sci 57 1583, 1968. 

Step 1. Filter sample through 0.45-/an silver-membrane filter and lower pH to 2.0 with HC1. 

Filters can be divided into two types membrane (screen) filters and depth filters. Membrane filters, such as silver membrane filters, physically screen and retain particles on their surfaces. These filters have uniform pore sizes and are rated for absolute retention all particles larger than the pore size are retained. Depth filters, such as glass-fiber filters, consist of a matrix of fibers that form a tortuous maze of flow channels. The particulate fraction becomes entrapped by this matrix. These filters do not have a uniform pore size, and it is not possible to rate them for absolute retention. They are rated according to nominal pore size, which is determined by the particle size that is retained by the filter to a predetermined percentage. This percentage is usually given as 98 retention however, it can be as low as 90. ... 

Figure 3. Variation of flow rate with filtration time for silver membrane and glass-fiber filters at 30 psi for Ogeechee River water. (Reproduced with permission from reference 11. Copyright 1985 John Wiley.)...

Free cyanide in aqueous solution can be determined indirectly by atomic absorption on the basis of its ability to dissolve silver as it passes through a porous silver membrane filter at pH 12.23... 

The analysis of particle bound PAH involves collection of PAH bound to dust particles on 0.8 pm glass fiber or silver membrane filters, desorption of PAH from the particles into a suitable organic solvent, and analysis of the extract by a capillary GC using an FID. Between 500 and 1000 L air at a flow rate of 120 L/h is recommended for sampling, which can give a detection limit of 0.15 to 0.50 pg/m3 for each compound (Riepe and Liphard, 1987). The method suggests the installation of an absorber resin, such as XAD-2 or Tenax, after the... 

Table I lists several XRD analytical methods recently developed in the NIOSH laboratories. For each analyte, the analytical range, detection limit and analytical precision are listed. The method numbers refer to the NIOSH Manual of Analytical Methods (2.). As indicated in the table, there are several NIOSH methods available for free silica analysis. Method No, P CAM 109 incorporates the internal standard approach as developed by Bumsted (3.), The other two methods S-315 and P CAM 259 are based on the substrate standard method. The major difference between the two is the direct sampling on silver membrane filters (S-315). This paper will address the various methods of quantitation, sample collection and procedures for matrix absorption corrections that have been used in this laboratory for the analysis of crystalline particulate contaminants in the workplace.

Eumstead ( ) chose native fluorite as an internal standard for the analysis of quartz in coal dust His procedure consisted of mixing 0 20 mg fluorite into each water suspension of standard and sample and depositing on silver membrane filters for a calibration curve (fluorite/quartz intensity ratio i[ . mg quartz) The application of this method to coal dust samples containing less than 1% quartz produced acceptable results relative standard deviation (RSD) was 18 2 ... 

Sampling procedures are often dependent on the method of sample preparation as well as the physical and chemical properties of the analyte For most analytes that are collected by the above method the usual procedure is to ash the filter in either a low temperature plasma asher or a muffle furnace, disperse the residue in a suitable liquid such as isopropanol using ultrasonic agitation, and filter the suspension through a silver membrane filter. In addition, if the internal standard method is used, the chosen standard must be added to the residue suspension prior to filtration ... 

The analytical procedure is as follows. Filter samples (both the glass fiber and the silver membrane) are placed in a screw-cap vial and five ml benzene (or alternative solvent) is added. The sample is extracted ultrasonically for 15 minutes. 

The extract is filtered through a 0.45 ym silver membrane filter and collected in an evaporator tube. The sample is extracted (2 ml solvent) two additional times and these extracts are collected in the evaporator tube. The combined extracts are concentrated to 1.0 ml under a stream of clean, dry nitrogen at 40 C. An appropriate aliquot of the extract is injected for HPLC analysis. Depending on the properties of the sample (e.g., analyte concentration), injection volumes may range from 1-50 yl. In our laboratory, samples are chromatographed utilizing the following conditions and parameters ... 

Figure 3. Chromatogram of HPLC analysis of an air sample from an aluminum reduction plant sample was collected on a glass fiber/silver membrane filter combination.

Porous glass has been available for transpon studies for several decades, but its use as a membrane material commercially started only in the early 1980s. Its uses have been mostly in the biotechnology area. Porous silver membranes were available in the mid-1960s in the form of tubes and later in the shape of a disk. The use of silver membranes, however, has been limited. Porous stainless steel membranes have been used for years as high-quality filters or supports for dynamic membranes. 

Silver membranes have been used as filters to collect clays or soils in a dispersion medium and then as an XRD substrate. In a typical analysis for mineral contents, a clay or soil is dispersed in water and vacuum filtered on the membrane. The silver membrane in this case has an advantage over ceramic membranes in that the XRD patterns of the minerals are distinctively different from that of silver. In conuast, the i>attems of the... 

The optimal mean filtration radius is an arithmetic average of pore radii measured on the surface of a membrane filter by means of electron microscopy and is used to characterize cellulose, nucleopore, and silver membrane filters. 

Filters can be divided into two types membrane (screen) filters and depth filters. Membrane filters, such as silver-membrane filters or cellulose-acetate and cellulose-nitrate filters, physically sieve and retain particles on their surfaces. These filters have uniform pore sizes and are rated for absolute... 

TABLE 3. Variation of Dissolved Organic Carbon Concentration as a Function of Filter Plugging for Silver-Membrane and Glass-Fiber Filters... 

This sample is not for the same data as silver-membrane filter sample. 

Filters can also sorb certain organic compounds possibly resulting in reduced recovery and fractionation of compounds of interest. Cranston and Buckley (1972) compared organic-membrane, glass-fiber, and silver-membrane filters for the sorption of humic acid. Organic-membrane filters sorbed 15%, glass-fiber filters 5%, and silver-membrane filters 3% of the humic acid in the solution passed through the filters. 

Silver-membrane and glass-fiber filters are recommended for studying particulate organic carbon, because organic contamination of the sample is avoided (Cranston and Buckley, 1972). These filters are also recommended for the isolation of aquatic humic substances, because interactions with the filter by dissolved organic compounds are minimized, and the potential for organic contamination of the sample is slight. 

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