Teflon filters

The particles most likely to cause adverse health effects are the fine particulates, in particular, particles smaller than 10 p and 2.5 mm in aerodynamic diameter, respectively. They are sampled using (a) a high-volume sampler with a size-selective inlet using a quartz filter or (b) a dichotomous sampler that operates at a slower flow rate, separating on a Teflon filter particles smaller than 2.5 mm and sizes between 2.5 mm and 10 mm. No generally accepted conversion method exists between TSP and PM,o, which may constitute between 40% and 70% of TSP. In 1987, the USEPA switched its air quality standards from TSP to PMk,. PM,q standards have also been adopted in, for example, Brazil, Japan, and the Philippines. In light of the emerging evidence on the health impacts of fine particulates, the USEPA has proposed that U.S. ambient standards for airborne particulates be defined in terms of fine particulate matter. 

Teflon filter A chemical-resistant hydro-phobic filter composed of polytetraf-louroethylene (PTFE) used for industrial hygiene sampling. 

Air samples can be analyzed by passing a known volume of air through a Teflon filter to catch air particulates followed by an activated charcoal filter to trap any gas-phase materials. The Teflon filters are extracted with hexane, concentrated, and analyzed by GC/MS. The charcoal traps are desorbed with carbon disulfide, concentrated, and analyzed by GC/MS. No performance data were reported (Dannecker et al. 1990). 

Air (particulates and gas) Sequential collection on Teflon filters and charcoal tubes solvent extraction with hexane (filters) and carbon disulfide (charcoal tubes) GC/MS Not specified Not specified Dannecker et al. 1990... 

Anhydrous Copolymerization of NIPAAM and N-Acryloxysuccinimide (NASI). In a modification of the procedure of Poliak et al., (4), NIPAAM (5 g, 44 mmol), NASI (0.372 g, 2.2 mmol) and 2,2 azobisisobutyronitrile (AIBN, 0.021 g, 0.13 mmol) were dissolved in 50 ml of dry tetrahydrofuran. The magnetically stirred solution was degassed, heated to 50 C for 24 hours under positive nitrogen pressure, and allowed to cool. The reaction mixture was filtered (0.45 i teflon filter) and the filtrate volume reduced by half. Ether was added with mixing to precipitate the copolymer. 

There is no need to degas solvents, but filtration using 0.45-pm Teflon filters is indispensable. 

The acceptor resin, in a syringe fitted with a Teflon filter, was washed with MeOH (5x) and CH2C12 (5x) and was dried under vacuum for 24 h. The donor imidate (5 equiv) and 4-A molecular sieves (ca. 2-mm beads) were added and the mixture dried in vacuo for 6 h. Dry CH2C12 (2.5 mL) was added and the mixture was stirred at rt under N2 for 1 h. Freshly distilled TMSOTf (0.15 equiv with respect to donor) was added and the reaction stirred for 2h (reaction time depended on the donor but, on average, all reactions were complete after 2 h). The resin was filtered off, washed successively with MeOH (5x) and CH2C12 (5x), and dried. 

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. 

TWOMASS, was used to collect ambient aerosol on Teflon filters (Ghia Corp, Pleasanton, CA). The aerosol inlet used was designed so that large particles did not reach this sampler. 

A total of 154 samples were collected on glass fiber filters during January and February 1978 June and July, 1979 August, 1979 and February and March, 1980. During the last period 24 samples were also collected on teflon filters. 

Filters. HN03 is efficiently trapped out on nylon filters. Typically, two or more filters are connected in series. A schematic of such a filter pack was shown in Fig. 11.22 (Anlauf et al., 1988). A Teflon filter first removes particles from the airstream and a nylon filter then removes gaseous HNO,. In this particular system, a third filter (Whatman 41 impregnated with an aqueous solution of glycerol and citric acid) was used to trap NH3. After sample collection, each of the filters is extracted separately and nitrate, ammonium, and additional particle components collected on the Teflon filter are measured by ion chromatography. The sensitivity of this method for nitric acid and the other species is determined in part by filter blank values (i.e., nitrate on unexposed filters) and by the total amount collected and hence the sampling time used. Times of... 

Potential interferences in the measurement of nitric acid using this method include removal of gaseous HN03 on the Teflon particle filter and/or volatilization of particle nitrate collected on this Teflon filter. As discussed in Chapter 7, NH4N03 is a common particle component, but exists in equilibrium with gas-phase NH3 and HN03 ... 

Scrubbers. Mist chamber scrubbers have also been used for HN03. The airstream passes through a Teflon filter to remove particles and then encounters a mist of water that scrubs the HN03 out of the air. The nitrate concentration is measured in the aqueous scrubbing solution using ion chromatography (Talbot et al., 1990). 

This method has been used to analyze both symmetrical (C.I. Direct Red 28 and C.I. Direct Blue 6) and unsymmetrical (C.I. Direct Black 38 and C.I. Direct Brown 95) benzidine-based dyes. Based on this work, the application of the method to other benzidine-based dyes should be straightforward. When field samples are submitted for benzidine-based dye analysis, bulk samples of the dyes present in the sample also should be submitted. With these bulk samples, the analyst should be able to determine if this method is applicable to the various dyes submitted and if any interferences are present. The method presently has not been tested on field samples. An existing sampling method (J 3) for azo dyes and diazonium salts should be directly applicable to this method with a change from a cellulose ester to a Teflon filter. This change is necessary to insure quantitative recovery of the sample from the filter. 

Resist compositions were prepared consisting of the step 2 product (80 g), the photoacid generator, triphenylsulfonium nonafluorobutanesulfonate, (4.4 g), the base, tri-(2-methoxymethoxyethyl)amine (0.94 g), and solvents 1-methoxyisopropyl acetate 560 g) and cyclohexanone (240). Compositions were filtered through a Teflon filter with a pore diameter of 0.2 pm and then heated to 50°C for 20 hours and cooled. A polymer having an Mn of 7200 Da was then isolated. 

Freeze-drying. For a 7000-fold concentration, 70 L of drinking water was lyophilized in a Virtus Unitrap II. The dried residue was then divided into equal weights and packed into two columns (25 X 1.5 cm) with a sintered glass filter. The organic material was eluted consecutively with acetone, ether, and DMSO. The ether in the ether eluate was removed by rotary evaporation, and the dried residue was dissolved in DMSO. The DMSO concentrates were sterilized by filtration over a 0.2-/xm Teflon filter (Millipore). The acetone and DMSO concentrates were tested in the Ames test. 

Derivatization. Residue portions equal to 23> of each total sample volume were treated with equal volumes of 0.1 M AgNC>3 in CH3CN. These mixtures were heated 10 min on a steam bath and cooled. Any precipitates were removed by filtration on Teflon filters excess silver ion was removed by reverse-phase HPLC. 

To provide a stock solution for flameless atomic absorption, add 25 ml of HC1 (cone.) and make the volume to approximately 50 ml with water. Add 5 ml 0.125% arsenic solution (5.0 mg) and heat to boiling. Add 8 ml of hypophorous acid (50% ) and boil for 5 min. Cool and filter through two 5fi Teflon millipore filters. Wash with HC1 (1 1) and finally with water. Place millipore funnel and Teflon filters in a 50 ml beaker. Add two 1 ml portions of HN03 down the sides of the millipore funnel. Then heat to complete the dissolution of selenium and arsenic. Rinse off the funnel and millipore filters. Transfer to a 25 ml volumetric flask and add 10 mg. of nickel as Ni(N03)2. Make to volume with water. 

DLS- 700S light scattering photometer at 633nm, calibrated with benzene. The optical clarification was performed with teflon filters. The specific refractive index increment (dn/dc) was obtained with Chromatix KMX-16 reffactometer at the same wavelength, calibrated with NaCl solution. 

Methodology. Teflon filters exhibit the lowest HN03 retention of those in common use (12). Fluoropore (Millipore Corporation) and Zefluor PTFE filters (Gelman Sciences) of 0.5- to 2- xm pore size, are frequently used as prefilters in the filter pack method (FPM). With 47-mm-diameter filters, flow rates with the FPM from 10 to 20 L/min are typical. The 2- xm pore size Zefluor filter exhibited 97% efficiency for 0.035- xm particles at a face velocity of 33 cm/s, with a pressure drop of 1.0 cm Hg (1.3 kPa) (33). 

Spare parts that are needed are compression fittings and ferrules, plunger and injector rotor seals, an extra plunger and seals, column filters, and injector needle port seals. If you do not use pacification, you might want to keep a set of check valves on hand. I always have one coil each of 0.01- and 0.02-in tubing in addition to my column blank. A replacement solvent inlet line with a porous stone is useful in case of corrosion. If you filter solvents, you need cellulose, nylon, and Teflon filters. You also need a back-up lamp for your detector. 

---