Separation airborne sampling

Cascade impactors are instruments which have been extensively used for sampling and separating airborne particles to determine the aerodynamic size classification of aerosol particles. There are three kinds of cascade impactors inertial impactors, virtual impactors and particle trap impactors. 

Because a filter sample includes particles both larger and smaller than those retained in the human respiratory system (see Chapter 7, Section III), other types of samplers are used which allow measurement of the size ranges of particles retained in the respiratory system. Some of these are called dichotomous samplers because they allow separate measurement of the respirable and nonrespirable fractions of the total. Size-selective samplers rely on impactors, miniature cyclones, and other means. The United States has selected the size fraction below an aerodynamic diameter of 10 /xm (PMiq) for compliance with the air quality standard for airborne particulate matter. 

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. 

Cascade impactors. Cascade impactors provide information on particle or droplet size spectra within airborne sprays. The air is drawn through a series of chambers that allow sequential separation of different particle sizes based on their different velocities and masses. This type of collector is not as widely used as the sampling devices discussed previously because they are relatively difficult to operate and are expensive. Further information on this and other types of sampler for spray research can be found in the literature. ... 

Packed column technology has been used in airborne gas chromatographs for the separation and quantitation of sulfur species (46, 47) and peroxyacetic nitric anhydride (48). The combination of sample preconcentration and sensitive detectors has yielded detection limits that are superior to corresponding continuous sensors. For S02, a detection limit of 25 pptrv was claimed, and for peroxyacetic nitric anhydride the detection limit was roughly 60 pptrv for an 50-cm3 air sample. Analysis times for samples were on the order of 10 min. 

An operational definition is considerably more practical. Operationally determined species are defined by the methods used to separate them from other forms of the same element that may be present. The physical or chemical procedure that isolates the particular set of metal species is used to define the set. Metals extracted from soil with an acetate buffer is an operational definition of a certain class. Lead present in airborne particles of less than 10 pm is another. In water analyses, simply filtering the sample before acidification can speciate the analytes into dissolved and insoluble fractions. These procedures are sometimes referred to as fractionation, which is probably a more properly descriptive term than speciation, as speciation might imply that a particular chemical species or compound is being determined. When such operational speciation is done, careful documentation of the protocol is required, since small changes in procedure can lead to substantial changes in the results. Standardized methods are recommended, as results cannot be compared from one laboratory to another unless a standard protocol is followed [124], Improvements in methodology must be documented and compared with the currently used standard methods to produce useful, readily interpretable information. 

Airborne Radon Progeny. Scheme 1. Count the sample immediately on the germanium detector, recording the time interval from separation to filtration Record in Data Table 8.5 Then count again in one week, followed by a third... 

In addition to the need to monitor known problematic compounds, newer compounds are being identified as potential threats to humans and as such need to be monitored in the atmosphere. For example, researchers reported (10) that several chemical and instrumental analyses of HPLC fractions provided evidence for the presence of /V-nitroso compounds in extracts of airborne particles in New York City. The levels of these compounds were found to be approximately equivalent to the total concentrations of polycyclic aromatic hydrocarbons in the air. Since 90% of the N-nitroso compounds that have been tested are carcinogens (10), the newly discovered but untested materials may represent a significant environmental hazard. The procedure involved collecting samples of breathable, particulate matter from the air in New York City. -These samples were extracted with dichloro-methane. Potential interferences were-removed by sequential extractions with 0.2 N NaOH (removal of acids, phenols, nitrates, and nitrites) and 0.2 N H2S04 (removal of amines and bases). The samples were then subjected to a fractional distillation and other treatments. Readers interested in the total details should consult the original article (10). Both thin-layer chromatography (TLC) and HPLC were used to separate the compounds present in the methanolic extract. 

Before the 1960 s, the analysis of toxic elements in airborne materials employed separations and colorimetric determination for single-element problems, or spectrographic methods for multielement, multisample studies. Variable matrices in most aerosols sampled had prevented sensitive, but interference-prone, flame-emission methods from attaining much usage. The increased concern over the environmental effects of toxic elements in the late 1960 s resulted in a need for greater sensitivity and ease of operation in measurements of these elements. The many laboratories with increased responsibilities found AAS most useful because of its accuracy, sensitivity, and relative lack of matrix effects, plus the low cost of the equipment. 

Samples were run on a Supelco LC-18-DB HPLC column, 2.1 mm X 25 cm. The buffers were A= 0.1% TFA in Milli-Q water, B= 0.09% TFA in 70% acetonitrile and the gradient was 0% B, 5min. 0 - 10% B, lOmin. 10 -50% B, 60 min. 50 - 100% B, 25 min. 100% B, lOmin. Fractions were collected in 1.5 nd polypropylene tubes, which were precleaned with 0.1% TFA in 50% acetonitrile, using an Isco Foxy fraction collector with peak separator. The fraction collector was enclosed in a Plexiglas chamber which was under positive nitrogen pressure to minimize airborne contamination of fractions. Fractions were capped and stored at -20 C. Immediately before loading on the sequencer, TFA (ABI) was added to fractions (25% final) to minimize peptide losses due to adsorption to the tube or pipet tip (18). 

Smaller acidic sulphate particles may lose chloride and nitrate ions in the form of gaseous hydrochloric and nitric acid. Thus, the chloride in airborne sea salt may be driven off as hydrochloric acid, which may be subsequently absorbed by larger, less acidic particles. Similar chemical reactions can also take place in samples of particles collected on filters, particularly if the coarse and fine particles are not separated. The pressure drop across the filter may also cause evaporation of the more volatile components. The chemical analysis of the collected particles may then give a distorted picture of the true airborne composition of the aerosol. 

Hayakawa and co-workers have intensively developed HPLC techniques with on-line reduction of NPAC to aminoPAC (APAC) and chemiluminescence detection of APAC for trace analysis of NPAC, particularly of nitropyrenes. In this study, we examined the HPLC method for the analysis of novel NPAC, 3-NBA and 2-NTP in airborne particles including the interference of coexisting NPAC in the sample in separation and the efficiency of the on-line reduction to selective conversion of 3-nitrobenzanthrone, which has one carbonyl group, to detectable 3-aminobenzanthrone in the HPLC system. 

The biosensor and response system used a tiered approach. Samples of airborne biological material were taken continuously by the Joint Biological Point Detection System (JBPDS) equipment, which was not commercially available. Operation of these systems was monitored continuously at a separate control facility. Initial detection by the JBPDS equipment was followed by a second-tier assay analysis that, if positive, would result in physical collection of sampled material for additional analysis off-site. The confirmed second-tier analysis would result in notification of JBPDS leadership and shipment of a sample to the Utah Department of Health for further laboratory analysis. Because the confirmatory test would take 12-24 hours to complete, the primary function of the higher-tiered detection was to define treatment and decontamination responses (LP-3 options). Change in building or HVAC operation on the fifth and sixth floors would not be initiated until the Utah Department of Health analysis confirmed detection of a biological threat agent. 

An overview of capillary gas chromatography is presented. Selected environmental applications, such as PCB s in water, PAH s in airborne particulate matter, and TCDD s at the part-per-trillion level illustrate the separation and analysis of complex mixtures. The chromatographic performance, characteristics, and trade-offs of packed and capillary columns are described in terms of permeability and efficiency, sample capacity, choice of stationary phase, high temperature capabilities, quantitative accuracy, and the development of GC separation methods. 

Figure 3. Capillary GC separation of the total PAH fraction of an airborne particulate sample. Column was 11 m X 0.26 mm SE-52, and temperature programmed from 70° to 240°C at 2°jmin (4).

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