Sampling - Field Sampling: Principles and Practices in Environmental Analysis - page 133

sampling concepts are applicable to all sampling, as are using GPS and GIS. In a detailed
analysis of air, water, and soil, inorganic and organic gases, liquids, and solids, will be
determined. These analyses frequently require a sophisticated laboratory and
instrumentation that is expensive and time-consuming to operate, even when the
contaminant is known [19].
Often environmental sampling benefits from time-weighted average sampling.
Typically, placing an absorbent or cation or anion exchange polymer in contact with the
media, soil, water, or air to be sampled accomplishes this type of sampling. The polymer
is left in contact with the media for some time. It is then removed and the adsorbed
material extracted from it and analyzed. The absorbent can be extracted with a solvent, or
it may be heated to drive off the absorbed material. In the case of cation or anion
exchange resins, the extracting solution must contain a cation or anion that will replace
all cations or anions on the exchange resin.
The assumption is that the material adsorbed on the media is irreversibly attracted to
the absorbent under the conditions in the field. It is also assumed that the absorbent does
not become saturated during the
FIGURE 5.14 Rock showing various layers or horizons.
sampling time. If both these conditions are met, the amount of material on the sorbent
divided by the time it is in contact with the media will give the average concentration of
the contaminant in the media.
A word of caution is that there is another condition affecting the effectiveness of this
method; there must be continuous, intimate contact between the media and the sorbent