Filters nylon

A variety of formats for protein arrays are possible. For example, a set of antibodies can be gridded on a filter or slide and used to detect protein expression levels (Pandey and Mann, 2000). Another type of array consists of proteins from an organism arrayed directly on to a glass slide, nylon filter or in microtiter wells (MacBeath and Schreiber, 2000). This format could be used to map protein-protein interactions or to associate a catalytic function with a protein. 

Paper filters are available to filter LC mobile phases, but nylon filters are used more often. Why is that ... 

The immobilized lipase (0.1 g) in pH 7 phosphate buffer (25 mL) was added to 25 mL (20 mM) of ester stock solution in a 250 mL Erlenmeyer flask (reaction flask). The reaction flask was incubated in an incubator shaker at 40 °C with the agitation speed set to 200 rpm. Samples from the organic phase and aqueous phase were withdrawn at 24 h intervals over a 5-day reaction period. The samples collected were filtered using 0.45 pm nylon filter and injected into the HPLC system to determine the rate of resolution by monitoring both substrate ((/ ,5)-2-ethoxyethyl ibuprofen ester) and product (5-ibuprofen acid concentration). 

The biotransformation was monitored by analysing samples taken periodically by HPLC. Samples (450 pL) were withdrawn from the biotransformation medium, acidified with 1 M HCL (50 pi) to stop the reaction and stored on ice for 30 min. All samples were centrifuged at 23 000g for 10 min at 4 °C to remove the cell debris and the supernatant filtered into HPLC vials using nylon filters (0.2 pm). 

Figure 8 shows a typical F4PLC chromatogram of the tablet extract illustrating the complexity of the sample, which contains numerous natural components, excipients and additives. During the SP method development, it was found that extraction with a neutral aqueous buffer was problematic due the loss of one of the active ingredients by hydrolysis. The use of the PTFE filter was also important because this hydrolysis product, which is highly hydrophobic, was absorbed by nylon filters under the filtration conditions. 

FIGURE 8 HPLC chromatogram of a tablet extract of an OTC product from natural material showing many natural components including active ingredient (peaks labeled A ), preservatives P and degradants D . Note that Peak A2 was found to hydrolyzed into D under neutral extraction conditions and component D was found to be retained by Nylon filters. 

As discussed below with respect to measurement techniques for individual compounds, the filter material is optimized for the compound of interest. For example, nylon has been found to be effective for the adsorption of gaseous HNO-, (Spicer, 1977). However, care must be taken that the filter does not also remove other gases simultaneously that are measured downstream of the filter. For example, SOz has been shown to be taken up by nylon filters, forming sulfate, with the extent of conversion being quite variable (e.g., Chan et... 

Denuders have been used in several different ways. One is to extract the walls of the denuder and measure the adsorbed gas directly by ion chromatography. Denuders have also been used as difference denuders. For example, in nitric acid measurements, the combination of gas-phase HNO-, and particle nitrate has been measured using a nylon filter or Teflon-nylon filter combination in one sampling train. In a parallel sampling train, particulate nitrate alone is measured by first passing the airstream through a denuder to re-... 

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... 

An informal intercomparison of these two CIMS methods with a filter pack method shows generally excellent agreement between the mass spectrometric approaches and often, but not uniformly, good agreement with the filter pack method (Fehsenfeld et al., 1998). The latter was often high, which was attributed to interference from decomposition of ammonium nitrate to HNO-, + NH3 on the Teflon particle prefilter, followed by absorption of the HNO-, by the nylon filter. 

A brief informal intercomparison study of the mass spectrometry methods with a nylon filter pack method near Boulder, Colorado, gave average levels of 0.38-1.6 ppb when the wind carried air from the direction of the greater metropolitan Denver urban area and 0.14-0.56 ppb when the wind was downslope and westerly, where there are fewer emissions sources previous filter pack... 

Formation of Nitrate on Nylon Filters. Introduction. Since first proposed by Spicer (17), nylon filters have played a prominent role in measuring atmospheric PN and HNQ3. Their prominence may be ascribed to a... 

The nylon filter currently sold as l- xm pore size Nylasorb (Gelman Sciences), probably the most widely used filter for HN03 sampling in the United States, was initially marketed by Ghia Corporation. Until 1985, these filters were fabricated from nylon 6, a polyamide formed from the homopolymerization of e-caprolactam. More recently, Gelman, Sartorius, and other vendors have supplied filters fabricated from nylon 6,6, made by polymerization of adipic acid and hexamethylenediamine. 

Potential interferents collected by nylon filters include organic nitrates (e.g., PAN), N02, and HONO. Each can yield N02, which can be oxidized to N03" by 03 or other oxidants. Although not related directly to nitrate sampling, S02 retention in varying degrees was also of concern. 

The degree of retention of SO on these nylon filters was also assessed 0.14 ppm S02 was sampled at 20 °C, 80% RH, and 20 L/min (total dosages for each filter, 2600 xg of SO (19). At saturation, the artifact SO values with the S S filter, 56 1 xg, was lower than that for the Sartorius and Gelman nylon 6 filters, which ranged from 65 to 70 xg. 

Other Interferent Studies with Nylon Filters. Retention of HONO on Gelman Nylasorb (nylon 6) filters was tested 0.3 to 1 xg/m3 HONO was sampled in air (—50% RH) at 20 L/min with 47-mm filters for 16-23 h. At saturation, the filters contained 1.8 xg/cm2 N02 this result indicates less than 50% efficiency for HONO retention (19). Sampling 440 xg/m3 HONO at 20 L/min with 47-mm Gelman Nylasorb filters (nylon type unstated), Sickles and Hodson reported about 25% retention efficiency, with a similar saturation value, and noted that such retention was reversible. Substantial oxidation of HONO to N03 on the filter surface by 03 was demonstrated in laboratory and atmospheric trials (21). Perrino et al. (20) observed with 47-mm Gelman Nylasorb (nylon type unstated) filters an efficiency for HONO that increased from about 25 to about 90% as the flow rate decreased from 12 to 2 L/min, with saturation at —50 xg/filter. Nitrite to nitrate conversion on the nylon filter surface increased from 13% at 45 ppb 03 to 93% at 200 ppb 03. 

PAN is a potential interferent with daytime concentration maxima that can coincide with the HN03 maxima. However, early work by Joseph and Spicer (23) and later work by Fahey et al. (24) indicated that PAN is not a significant interferent in HN03 measurements relying on nylon-filter collection. The change in nylon-filter composition introduces a small degree of uncertainty to this conclusion. 

Talbot et al. reported that 03 can react with unwashed nylon filters to produce increased extractable N03 (25). The artifact HN03 was equivalent to about 0.1 ppb (0.25 xg/m3) under the conditions used this result suggests that the artifact would only be significant at background locations. 

Retention, on nylon filters as well as on the denuder, of atmospheric species other than HN03 that form N03. ... 

Poor precision at low concentration because the DDM is a difference method. The limit of detection is, therefore, relatively high. For example, with Nylasorb nylon filters exhib-... 

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