Large-volume sampling

Shoeib and Harner (2002) and Wania et al. (2003) separately developed large capacity passive samplers for integrafively monitoring the atmospheric transport of HOCs. The sorbents used in these devices act as an infinite sink for HOC vapors, and have been used earlier to actively sample large volumes of air and... 

The independence from a power supply makes PASs popular options for measurements of POCs in the remote alpine atmosphere, but they also limit the temporal resolution that can be achieved. Trying to combine the advantages of both PAS and active samplers, a flow-through sampler (FTS) was recently designed, which requires no external power source, but can sample large volumes of air in fairly short periods of time [18, 19] by rotating into the wind and have it blow through a series of PUF disks. The volume of air sampled can be estimated from wind speed records. The FTS will trap particles, but they cannot be analyzed separately from the gas phase POCs. 

FIGURE 16.12 Schematic representation of the LC LCD procedure (adsorption retention mechanism with a narrow barrier of adsorli injected in front of sample). Large volume of sample is depicted. The sample contains two polymers exhibiting different adsorptivities. The fast (SEC-like) elution of adsorbing polymer is hindered by the barrier of adsorli while the non-adsorbing species are freely eluted in the exclusion mode. Four stages of the process are shown. The peak focusing is demonstrated. 

For individual unit samples large-volume injections), average the counts obtained for the two or more 5-ml aliquot portions taken from the solution unit. Calculate the number of particles in each milliliter taken by the formula... 

Radionuclide stations sample large volumes of air to detect radioactive particles and noble gases released from atmospheric nuclear explosions and radioactive gases vented from underground and underwater nuclear explosions. These radionuclides can be carried great distances by winds. The presence and ratios of specific radionuclides provide evidence of a nuclear explosion. 

In this separation, a 10-mL sample (large volume) containing a solution in tert-butyl methyl ether (tBME) of the pyrolysate of 1 mg cellulose obtained at 600° C was injected (off-line pyrolysis). The PTV injector was programmed at 20° C initial temperature for 2 min. and ramped with 10° C/min at 250° C and kept at this temperature for 1 min. Then the injector was further heated at 300° C. The split vent purge time was 2.5 min. The oven temperature for the first dimension separation was kept at 35° C for 2.5 min. then heated with 30° C/min. at 55° C and further heated with 3° C/min. to 240° C. The detector used in the first dimension was an MS system, which allowed the identification of a series of compounds from this chromatogram. The peak identification is given in Table 5.2.2. 

Sample collection and preparation have advanced but are also important areas for improvement. The challenge is to adequately sample large volumes of air, water, solids, or surfaces for contamination in a time frame and with equipment that is operationally effective. Concentrating the target molecules into a much smaller volume without adversely affecting detection and identification is also difficult. 

The reason why Kr has not been applied as widely as H, H- He, or CFCs lies in the technical difficulties of detecting its minute concentrations in natural waters. Sampling large volumes of water is time-consuming and not always feasible. Laser-based resonance ionization mass spectrometry for Kr analysis is currently being developed (Thonnard et al. 1997),... 

Differential scanning calorimetry (DSC) was performed by using a Mettler DSC 30 at a rate of 10 K/min with a nitrogen purge, the flow rate of which was adjusted to 50 mL/min. For wet samples, large-volume stainless steel pans that sealed with an o-ring (Perkin-Elmer) were used to prevent evaporation. 

Because of the relatively large amount of dust necessary for substance-specific analysis, stationary samplers capable of sampling large volumes of air have to be used to collect sufficient material for an accurate analysis. The already mentioned Gravikon VC 25, furnished with a fine-particle sampling head, is an example of a sampler for this task [6-109]. Like other fine dust samplers, this stationary device meets the requirements of the "Convention of Johannesburg (see Section 2.10). 

The volume of the sample that can be applied to the centrifuge tube depends upon the cross sectional area of the gradient exposed to the sample. Thus centrifuge tubes of limer diameter of 2.5 cm will accommodate only about upto 1 cm while tubes with diameter of 1.6 cm will accommodate only about 0.5 cm of sample. Large volume of sample, if added, will result in loss of proper resolution through broadening of the separated zones. Lesser volumes of sample will not affect resolution but might be difficult to detect after separation. 

Water for the analysis of suspended particles may be collected with any clean water sampler used for oceanographic work, e.g., Niskin bottles, Go-Flo bottles, Nansen bottles. Hydrobios water samplers (see also Chapter 1). The sample volume will depend on the expected concentration of POM. In nearshore and/or biologically productive water, 0.5-2 L usually is an adequate sample volume. Ten litres may be required in particle-poor open ocean waters such as the Sargasso Sea. For sampling large volumes of water, 30 L Niskin bottles are recommended. Even larger volumes may be sampled with in situ pumps. (See Chapters 1,2 and 13). 

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