Polytetrafluoroethylene filter

Fig. 4.6.8. (Right) Example of the fixed column end fitting for glass columns, suitable for water and organic solvents (after Ref. 18). 1, inlet capillary 2, thrust screw 3, seal made of soft polytetrafluoroeth-ylene 4, end fitting body made of plastics or metal 5, polyamide or polytetrafluoroethylene filter 6, cap nut 7, seal ring made of polytetrafluoroethylene powder or powdered mixture of graphite and polytetrafluoroethylene 8, rubber rings 9, column.

The success of this and the other operations derives from the correct application of back-pulse filtration principles, in particular the back-pulse step itself in which the filter cloths are cleaned and made ready for further filtration. The properties of the GORE-TEX membrane, composed of expanded polytetrafluoroethylene, give rise to the desirable results of these brine filtrations, in particular ... 

The mobile phase is a solution of methanol acetonitrile water (53 23 24) containing 30 mM ammonium acetate adjusted to pH 5.6 with acetic acid this solution is filtered through polytetrafluoroethylene 0.45-pm filters. 

Combination Methods. Combination methods refer to those methods that employ both concentration and isolation methodologies. The modified parfait-distillation method that was evaluated used a series of adsorbents coupled with vacuum distillation to recover unadsorbed solutes (11). Porous polytetrafluoroethylene (PTFE) was used to adsorb the hydrophobic neutrals, and in field sampling it serves as a filter for particulate removal. Cation- and anion-exchange resins were then used to remove the ionized organic substances and to deionize the sample prior to the concentration of the nonadsorbed hydrophilic neutrals by vacuum distillation. Organic constituents were selectively... 

All the filters used must comply with the demands made by regulatory authorities. In sterilizable systems, hydrophobic diaphragm filters made of either polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE) with a diaphragm pore width of... 

Filters can be grouped on the basis of different characteristics. For example, they can be grouped on the basis of the design capacity of the filters according to the particle concentration or loading [Svarovsky, 1981] or they can be grouped on the basis of the materials of the filters, e.g., fabric or nonfabric [Cooper and Freeman, 1982], Most filters in use are bag filters, which are fabric. The common fabric materials include cotton, polyester, wool, asbestos, glass, acrylic, polytetrafluoroethylene (Teflon), poly (m-phenylene isophthalate) (Nomex), polycaprolactam (Nylon), and polypropylene. 

In developing a method that requires filtration, adsorption of the analyte onto the filter must be taken into account. For dilute solutions of adriamycin, >95% is adsorbed to cellulose ester membranes and about 40% to polytetrafluoroethylene membranes [19]. For more concentrated solutions, as would be encountered in bulk formulation testing, filter ad-... 

All samples were filtered with a 0.45pm polytetrafluoroethylene (PTFE) membrane filter before injection into the column. 

This kind of contamination was carefully evaluated by using various labware glass and quartz tubes, polytetrafluoroethylene (PTFE) vessels, fluorinated ethylene propylene (FEP) and perfluoroalkoxy (PFA) tubes. Ideally, all trace element determinations should be carried out in clean rooms in which the incoming air is filtered and special clothing is worn. 

Sample Preparation Transfer about 0.1 g of sample, accurately weighed, into a 4-dram vial. Add between 0.010 to 0.015 g of diphenyl ether, accurately weighed, 10 mL of toluene, and 5 drops of 10% sodium hydroxide solution cap the vial and shake well. Allow the vial to stand until the caustic layer settles to the bottom, and filter the neutralized sample through a 0.45-p.m polytetrafluoroethylene (PTFE) filter, or equivalent. 

One of the most successful industrial applications of polymeric catalytic membranes is the Remedia Catalytic Filter System to destroy toxic gaseous dioxins and furans from stationary industrial combustion sources by converting them into water, CO2, and HCl. The system consists of an expanded polytetrafluoroethylene (PTFE) microporous membrane, needle-punched into a scrim with a catalytically active PTFE felt. The catalyst is a V2O5 on a Ti02 support. The microporous membrane captures the dust but allows gases to pass to the catalyst where they are converted at temperatures as high as 260° C. 

Precursors and catalysts were characterized in ambient conditions by X-ray diffraction (XRD) on a Rigaku Powder Diffractometer using CuK radiation with a Ni filter. LiF was used as an internal standard for the activated catalysts. Laser Raman spectra (LRS) were collected using Ar ion laser excitation (514.5 nm) at a power of 25 mW at the sample. Spectra for the precursors were collected in ambient conditions, and reaction-used catalysts were characterized in-situ at 400°C in a 70 ml/min flow of C4H,(/02/He (0.99/10.2/88.81). Phosphorus to vanadium ratios (molar) were determined by inductively coupled plasma (ICP). Diffuse reflectance spectra (DRS) were collected in ambient conditions using polytetrafluoroethylene as a reference. 

Polymeric membranes are prepared from a variety of materials using several different production techniques. Table 5 summarizes a partial list of the various polymer materials used in the manufacture of cross-flow filters for both MF and UF applications. For microfiltration applications, typically symmetric membranes are used. Examples include polyethylene, polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) membrane. These can be produced by stretching, molding and sintering finegrained and partially crystalline polymers. Polyester and polycarbonate membranes are made using irradiation and etching processes and polymers such as polypropylene, polyamide, cellulose acetate and polysulfone membranes are produced by the phase inversion process.f Jf f ... 

Depending on the amount of compound available, replicate experiments should be carried out. After stirring or shaking, the solvent should be separated from the suspension by centrifugation or by filtration using polytetrafluoroethylene (PTFE) filters. The filtrate is then assayed preferably by HPLC however, UV-visible spectroscopy can also be used to determine the solubility, if compound stability or impurities are not an issue. This is termed the thermodynamic solubility. It is also useful to measure the pH of the filtrate and to analyze any undissolved material by DSC to detect any phase changes that may have occurred. 

For gas filtration, the membrane should be treated to make it hydrophobic if not already inherently so. Membranes made from polytetrafluoroethylene or polypropylene are already nonwetting, and wettable polymers are treated by the manufacturer to render them hydrophobic. If the gas filter is hydrophilic, water condensing on the filter or entrained by the gas will wet the pores and be retained by capillary action unless the differential pressure across the filter exceeds the "bubble-point" pressure. In this case, the filter is "blinded" by water and the flow is restricted considerably. 

Sterile filtration of liquids and gases is now virtually always done using mem brane filters. The first U.S. patent for membrane filters was filed in 1922 and pertained to cellulose acetate membranes. A wide range of membrane filter media are now commercially available to suit various applications cellulose esters, polyvinylidinefluoride, polytetrafluoroethylene (PTFE), and polyhexam-ethyleneadipamide (nylon 66), separately or as laminates with polyethylene, polypropylene, and polyester for more robust phy.sicai characteristics. 

Electrochemical studies of the electrocatalysts were carried out using the thin porous coating technique [12,13]. An amormt of 20 mg of the eletrocatalyst was added to a solution of 50 mL of water containing 3 drops of a 6% polytetrafluoroethylene (PTFE) suspension. The resulting mixture was treated in an ultrasound bath for 10 min, filtered and transferred to the cavity (0.30 mm deep and 0.36 cm area) of the working electrode. The quantity of electrocatalyst in the working electrode was determined with a precision of... 

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