Mitex filters

The Mitex filters are also made of Teflon, but have no backing material. A 5 ym pore size Mitex filter was used because it is the smallest pore size available. Each of these is available in 37mm diameter disks and can be used in convenient, 3-piece polystyrene filter holders (Millipore Aerosol Monitors). Extracts of samples collected on these filters were tested for stability by conducting the following experiments. 

As shown above extracts of organoarsenicals obtained from cellulose ester filters and analyzed by the developed method suffer severely from lack of stability. To evaluate conclusively and also to find an appropriate filtering medium, experiments were performed to simultaneously test the stability of organoarsenicals on cellulose ester, Fluoropore, and Mitex filters. The experimental design is outlined in Figure 1. 

Figure 1. Experimental design used to test and compare the stability of organoarsenicals on cellulose ester, Fluoropore, and Mitex filters. Triplicate spiked filters were used for each experiment.

On the basis of these results, it is clear that a more inert filter material, Mitex or Fluoropore, should be used. As will be discussed below, the collection efficiency of the Fluoropore filters is better than that of the Mitex filters, and for this reason it was finally decided to use Fluoropore filters for the combined sampling and analytical procedure. 

Table VI. Collection efficiency of Fluoropore and Mitex filters for...

Use a solvent resistant filter disc made from such materials as Millipore LSWP 04700, (Mitex-Teflon), Millipore URWP 04700, (Solvinert), or Gelman VF-6, (Fluoride-Metricel), plain, white, 1 Ot3 microns, 47mm diameter instead of the filter specified in Method 2276-65T... 

Three commercially available filtering media were evaluated for the collection of airborne particulates of the organoarsenical compounds. These were cellulose ester, Fluoropore, and Mitex membrane filters. The evaluation was based on the following requirements l) the collection medium must quantitatively collect the particulates 2) the collection medium must be capable of. retaining the compounds without loss or chemical change before analysis 3) the collected species must be extracted quantitatively from the collection medium for analysis and b) the method must be efficient at temperatures up to 50°C and a relative humidity of... 

Three filtering media commercially available from Millipore Corporation were evaluated for the collection of airborne particulates of the organoarsenical compounds. These were (l) cellulose ester membranes (2) Fluoropore and (3) Mitex. The cellulose ester membrane filters (0.8 ym pore size) are the standard Millipore filters used for aerosol sampling and consist of a mixture of cellulose nitrate and cellulose acetate. The Fluoropore filters are made of Teflon (PTFE) and are bonded to a polyethylene net. Fluoropore filters with a pore size of 1.0 ym were selected for this study. 

The collection efficiency of the Mitex and Fluoropore filters was tested by generating and collecting mixed aerosols containing MMA, DMA and p-APA under controlled conditions and analyzing the resulting filter extracts by the developed analytical technique. 

Organoarsenical Species Filter Stage Fluoropore 1.0 ym Mitex 5.0 ym... 

The GPC instrumentation and GPC procedures used here are the same as described earlier (I) but with slight alterations. The Kroeger HAK-1 pads furnished with the pressure filter were replaced by Millipore 5-/x Mitex membranes to reduce changes in solution concentrations arising from adsorption of the solute on the fibrous material of the pad. When retention of eluted fractions was desired, two shallow aluminum pans filled with tetrahydrofuran (THF) were placed in the syphon box, and then the door was closed and latched. The saturation of the enclosed air space by THF vapor minimized evaporation of the solution during drop formation, drop fall, and retention of fraction in the syphon. The possibility of diluting the sample solution when charging the sample loop was... 

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