Specific samplers

A large range of home-made equipment is used to sample at interfaces to the sediment and the atmosphere or across internal density discontinuity layers or redox (chemo-)clines e.g.. Bale and Barrett, 1995 Eversberg, 1990 Hallberg et al, 1977 Schwedhelm et al, 1988  

Sternberg et ai, 1991). For different vertical resolutions, the water is collected in multi-chamber samplers. The transport is performed across filter and dialysis membranes, either actively by suction via pumps and vacuums or passively driven by concentration gradients and diffusion. 

Sampling techniques for subsequent analysis of radioactive tracers in seawater are described in detail in Chapter 13. 

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Volume of water or air cleared ( v) by a specific sampler configuration at equilibrium. We use PCB congener 52 in diis example. 

Permeation systems can be calibrated in the laboratory and then used in the field for sample collection for a fixed period of time, e.g., 8 hr or 7 days. The sampler is returned to the laboratory for analysis. These systems can be made for specific compounds by selecting the appropriate collection medium and the polymer membrane (Table 13-2). 

Direct reading samplers include simple devices such as colorimetric indicating tubes in which a color change indicates the presence of the contaminant in air passed through the tube, or instruments which are more or less specific for a particular substance. In the latter category are carbon monoxide indicators, combustible gas indicators (explosimeters) and mercury vapor meters, as well as a number of other instruments. 

For HPLC, the injector is a valve. In the charge position, a 50- jL syringe is used to fill the sample loop that holds a specific volume of sample solution. The valve is switched to the run position, and the eluent carries the sample out of the sample loop and into the column (auto samplers are also available for HPLC). A recording of the detector output is automatically started at the time of injection and produces a chromatogram of the separated components. 

In an effort to optimize the solvent-containing passive sampler design, Zabik (1988) and Huckins (1988) evaluated the organic contaminant permeability and solvent compatibility of several candidate nonporous polymeric membranes (Huckins et al., 2002a). The membranes included LDPE, polypropylene (PP), polyvinyl chloride, polyacetate, and silicone, specifically medical grade silicone (silastic). Solvents used were hexane, ethyl acetate, dichloromethane, isooctane, etc. With the exception of silastic, membranes were <120- um thick. Because silicone has the greatest free volume of all the nonporous polymers, thicker membranes were used. Although there are a number of definitions of polymer free volume based on various mathematical treatments of the diffusion process, free volume can be viewed as the free space within the polymer matrix available for solute diffusion. 

Similar to the previous section, we discuss only selected works to highlight the development of SPMDs. Also, we include some discussion of several unpublished pilot smdies (Huckins, 1989) that influenced our early development of SPMDs. These pilot studies were directed solely toward sampling the aqueous phase. The flrst application of SPMDs for sampling organic vapors did not occur until several years later (Petty et al., 1993). To our knowledge, only SPMDs, PESs and SPMEs are being applied in both air and water, because the use of many passive samplers is limited to a specific medium and exposure scenario. 

This configuration has still another potential bonus. For the upstream sampler, especially in the loop configuration, it is not advantageous to employ large-diameter piping. Indeed it is optimal to specifically use a narrow diameter. 

In 1995 Hewlett Packard introduced the HP 6890 series of instruments which are designed to fulfil a broad range of analytical requirements. TTiis series includes a specific automatic fiquid sampler for increased throughput and automation, a series of options for data-handhng/control for the gas chromatograph and samples, as well as an integrator that supports the fuU range of features provided. 

A promising development is that reported by Rheingrover and Gordon (30). Using ambient samplers located in "maximum effect" areas for specific sources and wind flow patterns, they have distinguished the composition of a single point source a a receptor. They then use these source characteristics to represent that source in areas less affected by that source, where its contribution is not so obvious. 

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). 

A universal sampler applicable to the majority of pesticides would be an ideal sampling device. In this study, personal sampling and analytical methods were developed and validated in the laboratory for determining workplace exposure to several pesticides. The major objectives of the study were to standardize on specific sampling media and to develop and validate methods using filter/ sorbent sampling trains. 

Another sensor system that further expands the capabilities of the Chronotox is the Personal Tape Sampler (PTS). The PTS (Figure 5) is a miniaturized gas monitor designed primarily to be worn by a worker during his entire workshift. It operates on the principle of specific chemical colorimetric reactions occurring on a dry chemically impregnated paper tape and gives... 

The PTS uses the principle of a specific colorimetric reaction, each toxic substance being detected by a reaction system specific to that gas. This principle provides the capability for extreme sensitivity down to less than one part per billion (10 ) while maintaining excellent specificity. Reactive chemicals are impregnated onto a continuous paper tape by a special process producing a dry reaction system. The tape is put into cassettes for convenient use and replacement in the Personal Tape Sampler (PTS). 

A colorimeter (Figure 4) has been designed specifically for analyzing >2/ ) passive samplers. It is lightweight, portable and simple to use. Features incorporated into the unit include a ten-minute timer with audible alarm to ensure complete color development of the samples before analysis, a cuvette slot which... 

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