Trapped air samples

The first quantitative experiments on gases were performed by an Irish chemist, Robert Boyle (1627-1691). Using a J-shaped tube closed at one end (Fig. 5.3), which he reportedly set up in the multistory entryway of his house, Boyle studied the relationship between the pressure of the trapped gas and its volume. Representative values from Boyle s experiments are given in Table 5.1. These data show that the product of the pressure and volume for the trapped air sample is constant within the accuracies of Boyle s measurements (note the third column in Table 5.1). This behavior can be represented by the equation... 

What would have happened if Boyle had allowed the temperature of the trapped air sample to change as he added mercury to the tube ... 

The most common methods for trapping pesticide vapors from air use adsorbents. Common air sampling adsorbents include charcoal (derived from petroleum or coconut) and synthetic polymeric materials, such as cross-linked polystyrene and open-cell polyurethane foam. Charcoal has been used for the cumulative sampling of volatile... 

The adsorbent also needs to be spiked directly with the chemical to determine the recovery from the adsorbent, and this recovery value can be used to adjust the recovery from the adsorbent after air sampling. For compounds with extremely low volatilities, the chemical deposit can be heated to promote volatilization and to minimize the time required for the trapping experiments. 

For the charcoal, XAD, and PUF adsorbents discussed above, solvent extraction techniques have been developed for the removal and concentration of trapped analytes. Although thermal desorption has been used with Tenax-GC in some specialized air sampling situations [primarily with sampling volatile organic compounds (EPA, Method TO-17 )], this approach is not a viable alternative to solvent extraction for the charcoal, XAD, and PUF adsorbents. The polystyrene and PUF adsorbents are thermally unstable and the charcoal chemisorption bonding is more easily broken by... 

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). 

In polar ice sheets air gets continuously trapped, and ice cores obtained by drilling through the ice caps therefore constitute a continuous set of ancient air samples. 39Ar/Ar and 81Kr/Kr measurements on these samples primarily reflect the production rates of these radioisotopes averaged over a few half-lives. 

There are several combinations of Couette available. The simple bob shown in Figure 3.4 has a concave base, which is designed to trap air in order to reduce the drag contribution from the base. This geometry usually has a larger area and delivers a larger torque for a given sample... 

Chai M, Pawliszyn J. 1995. Analysis of environmental air samples by solid-phase microextraction and gas chromatography/ion trap mass spectrometry. Environ Sci Technol 29 693-701. 

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