Aerosol filters

Si(Li) spectroscopy, with the capability of simultaneous quantitative analysis of 72 elements ranging from sodium through to uranium in solid, liquid, thin film and aerosol filter samples. The penetrating power of protons allows sampling of depths of several tens of microns, and the beam itself may be focussed, rastered or varied in energy. The use of a proton beam as an excitation source offers several advantages over other X-ray techniques, for example there is a higher rate of data accumulation across the entire spectrum which allows for faster analysis. 

As PCR is a powerful method used to obtain millions of copies for each template molecule, there is a considerable contamination risk. Small amounts of PCR products from previous experiments as well as DNA molecules from other sources can cause spurious results and false interpretations. It is therefore strongly recommended to wear gloves and to pipette with tips containing aerosol filters. Moreover, PCR products should not be handled in the same room where the PCR reagents are being used. 

For studies of element 108 (Hs) and element 112 the new device named In-situ Volatilization and On-line detection (IVO) was developed [124], By adding 02 to the He carrier gas, volatile tetroxides of group-8 elements were formed in-situ in the recoil chamber. A quartz column containing a quartz wool plug heated to 600°C was mounted as close as possible to the recoil chamber. The hot quartz wool served as an aerosol filter and provided a surface to complete the oxidation reaction. For future studies with element 112 pure He or even a reducing He/H2 mixture can be employed. 

For automated routine measurements usually the y activity is determined by means of Geiger-Muller or scintillation counters. Additional measurements are made by filtering off aerosols from the air and by taking samples of water, soil or plants. The samples may be dried or processed by chemical methods for more detailed investigations. The a, or y activities on the aerosol filters and in the processed samples are measured by means of proportional counters or a and y spectrometers, by which the radionuchdes can be identified. 

Contamination is a major problem in quantitative PCR methods. The most common type of contamination is with PCR product from previous reactions, which may be aerosolized during preparation for gel analysis. PCR product contamination can be found on the benchtop, on pipetmen, and on the thermal cycler itself. The use of dedicated sets of PCR pipetmen (one pre-PCR, and one post-PCR), and pipette tips with aerosol filters helps prevent this problem. We monitor for contamination by amplifying a water-alone sample for 10 cycles more than the PCR reaction being performed. When contamination is detected, new PCR buffers are generated and reactions are run again. 

This protocol must be performed by authorized personnel and according to the rules and regulations for work with radioactive substances. Use pipette tips provided with an aerosol filter to avoid radioactive contamination of the pipette. This procedure can be accomplished in 2 h. 

The limit to the effectiveness of a gas cleaning device is its efficiency ip the removal of aerosols. Neither electrical nor thermal precipitation has proven practical for the rapid removal of aerosols, and filtration seems to be the best method of removal. Aerosol filters consist of loosely aggregated fibers, and in order to avoid excessive resistance to flow of gas, the mesh of the fiber must be larger than the size of the particle to be removed. There is therefore no screening action the removal of the particle depends entirely upon a chance collision of the particle with a fiber of the filter. Once having collided, the particle adheres by adsorptive forces. 

Some instrumental methods (INAA, XRFA) analyse directly the aerosol filter or portions of filters. Recently such approach is intensively tested for other methods especially ETAAS. For the majority of instrumental methods however treatment of the filter is required leading to a liquid extract. Wet ashing with different acidic mixtures is very popular though dry ashing in a furnace, followed by acid dissolution is also used. The choice of the method depends not only on the measurement technique and the range of substances to be analyzed but also on the chemical form of the element (Kneip and Kleinman, 1982). For example high temperature secondary aerosols may contain refractory oxides or silicates and the treatment requires fusion or hydrofluoric acid dissolution. 

Between five and 15 elements can be determined in aerosol filters, including some rare earth elements and Zr in concentrations down to 0.17 ng/g (Cresser et al., 1988, 1992 Ebdon et al., 1987). 

ETAAS is used to determine about 15-20 elements in aerosol filters, usually after acid extraction. Preconcentration adds about five to six more elements. In soils and plants the method permits the direct determination of about ten to 15 elements after dissolution of the samples. 

An excellent review on the use of INAA in the analysis of aerosols can be found in (Allan and Sansoni, 1985, 1990). Over 25 elements are easily and reliably determined in different aerosol filters. The use of epithermal and thermal irradiations increases the analytical parameters of the analysis for some of the elements (Allan et al., 1984, 1985). Forty-one elements have been successfully determined in combustion effluents from power plants (James and Acevedo, 1993). 

These compounds are nearly always disseminated as aerosols. As such they do not interfere with the activated carbon, but are retained by the aerosol filter. It is possible that, due to reactions such as hydrolysis, or as part of the spraying system, organic vapours are released by the aerosol particles. If this is the case, these vapours will be retained by die activated carbon on die basis of pure physisorption. 

For the sampling of aerosols, filters are the most commonly used collection substrates, but a variety of films and foils have been used with impactors to collect size-resolved samples. Sampling times vary with ambient loadings, sampling rates, substrate blanks, and analytical sensitivities but typically vary from several hours in urban areas to a day or more under clean background conditions. 

Totally, 48 aerosol filter samples were used for the analysis of water-soluble diacids and related compounds using the method described in Kawamura and Ikushima (1993) and Kawamura (1993) with some modification. Briefly, aliquots of the filters were extracted with pure water (5 ml X 3), followed by the extraction with ethyl acetate (5 ml X 3). The latter solvent was used to extract fatty acids and other lipids. The extracts were combined and concentrated using a rotary evaporator under vacuum and then dried using a nitrogen blow-down... 

If inspired particles were carried only convectively with the bulk of airflow, losses of these particles in the respiratory tract would be negligible. However, all inspired particles experience a nonzero chance of being lost. This is due to particle transport toward airway and airspace surfaces as a result of mechanical and electrical forces acting upon the particles. Upon contact with these surfaces, the particles are deposited. The human respiratory tract can therefore be considered as an aerosol filter, removing particles from the inspired air. The effectiveness of this filter depends on... 

The first version of such system is presented in Fig. 2. The air samples from the exhaust ventilation pipeline are pumped through a special aerosol filter where sodium aerosols are accumulated. The radiometer measures the filter radioactivity and generates a signal at an excess of some specified level. This system showed very high operating characteristics. 

More recently, a composite aerosol filter media has been prepared by depositing polyvinyl alcohol (PVA) nanofibres with mean diameters of about lOOnm on nonwoven fabric substrates by using needleless electrospinning technique. The filtration performance of the composite filter was evaluated by measuring the filtration of sodium chloride nanoparticles (75 20nm). The results showed that the filtration efficiency of the composite filter media for nanoparticles was increased with the increase in thickness of the nanofibre mats, which was controlled by the deposition time of the electrospinning process. 

In the last few years, new procedures were developed for PAH analysis using MS-based detection methods. GC-IT-MS and a laser desorption-IT-MS screening method were applied to the analysis of airborne particulate-associated PAHs. Direct screening of aerosol filter samples were carried out using laser desorption TOF-MS. Isotope dilution techniques using GC-MS were also developed for some PAHs, such as benzo[a]pyrene. 

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