Passive samplers extraction sampler

Various types of detector tubes have been devised. The NIOSH standard number S-311 employs a tube filled with 420—840 p.m (20/40 mesh) activated charcoal. A known volume of air is passed through the tube by either a handheld or vacuum pump. Carbon disulfide is used as the desorbing solvent and the solution is then analyzed by gc using a flame-ionization detector (88). Other adsorbents such as siUca gel and desorbents such as acetone have been employed. Passive (diffuse samplers) have also been developed. Passive samplers are useful for determining the time-weighted average (TWA) concentration of benzene vapor (89). Passive dosimeters allow permeation or diffusion-controlled mass transport across a membrane or adsorbent bed, ie, activated charcoal. The activated charcoal is removed, extracted with solvent, and analyzed by gc. Passive dosimeters with instant readout capabiUty have also been devised (85). 

The primary role of SPMDs and other passive samplers is to provide convenient, powerful analytical tools for determining dissolved and vapor phase HOC concentrations in environmental systems. This chapter has shown that they are also useful as biomimetic screening tools for estimating exposure of organisms to bioconcentratable compounds and for deriving BCFs based on EP theory. Even for those chemicals that are present at vanishingly small amounts in the dissolved phase and are primarily accumulated via the dietary uptake, SPMDs generally extract sufficient amounts of residues for analysis. 

Finally, passive samplers have also been developed for ozone, primarily for use in epidemiological studies. For example, Brauer and Brook (1995) describe the application of a passive sampler in which air containing ozone diffuses through a Teflon membrane and reacts with nitrite. The sampler is then extracted and the nitrate product measured using ion chromatography. 

Passive samplers are used for specific applications such as for indoor air environments or as passive dosimeters. In this approach, the air containing the organic diffuses to and adsorbs on a solid sorbent without active pumping. The organics are subsequently thermally desorbed or extracted from the sorbent using a solvent (e.g., see Shields and Weschler, 1987). 

Analytes may accumulate in the sorption phase either by adsorption onto the surface of solid sorbent materials or by absorption in absorbent liquids or polymers that behave like subcooled liquids.The advantage of solid adsorbents is the potential to select materials with a high affinity and selectivity for target analytes. However, the sorption capacity of adsorbents is usually limited, and the description of adsorption/desorption kinetics of analytes to adsorbents is complex. Typically, the adsorbent materials used in passive samplers are similar to those used in solid-phase extraction techniques. 

Hyne, R.V., F. Pablo, M. Aistrope, A.W. Leonard, and N. Ahmad. 2004. Comparison of time-integrated pesticide concentrations determined from field-deployed passive samplers with daily river-water extractions. Environ. Toxicol. Chem. 23 2090-2098. 

Passive samplers place an adsorptive surface (frequently charcoal-based) a fixed distance from a windshield or semipermeable membrane in an enclosure in which the windshield or membrane is exposed to the air being sampled. These devices generally require that a minimum air movement across the windshield or membrane occurs in order to ensure that the device is sampHng properly. The concentration of the contaminants of interest will determine the minimum exposure time of the passive sampler. The major advantages of this type of sampler are that the collection devices are small, require no electrical power and are very easy to use. After exposure, which can, for some devices, extend to periods as long as 6 months or more, the adsorbent is removed and extracted. The extract may have to be reduced in volume prior to analysis. As with other non-specific adsorbents, the passive sampler adsorptive surface will trap a wide variety of compounds. Oxidation of the adsorbed compounds may be a problem if the passive sampler is left for a long period in a gas that contains oxidants. 

Method b in situ extraction with passive samplers filled with hexane. 

Solid-phase microextraction (SPME) devices can be employed with solid samples as passive samplers, but this approach must be conducted in headspace mode and so it is limited to the more volatile PAHs [269], Furthermore, it appears that SPME is a better approach to extract primarily PAHs present in sediment porewater rather than in the colloidal phase [270], EPA method 8272 describes the determination of parent and alkyl polycyclic aromatics in sediment pore water by SPME-GC-MS. In a similar way, SPMDs have been mainly used for the determination of PAHs contained in sediment porewater [271],... 

Diffusive samplers have also been developed to determine SVOCs but there have been relatively few studies to date. An example is the passive flux sampler developed by Fujii et al. (2003) to determine the rate of emission of phthalate esters from materials. The sampler consisted of a circular metal disc containing activated carbon particles held within an inert matrix of PTFE. The sampler was placed on the material under test giving a diffusion length of 0.5 or 2 mm depending upon the design and adsorbed phthalate esters were extracted from the sampler with toluene and determined by GC-MS. 

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