Presampling - Field Sampling: Principles and Practices in Environmental Analysis - page 72

by Teflon.
Bottles and vials with lined crimp-on caps are also common. Crimped tops require a
crimping tool and a separate top and liner. A sample is placed in the container. A liner is
added and then crimped in place. Such tops are not easily removed, so tampering is not
possible and accidental loosening and spillage is prevented. Special crimped top removal
tools are also readily available.
Both bottles and vials may have caps, either crimped or screw-on, with a hole in the
center so that samples can be taken directly from the bottle using a syringe. Direct
removal of a sample from the bottle without opening it prevents unintentional
contamination. When applicable, these can be timesaving, as the bottles can be purchased
to fit an automatic sampler.
Glass bottles have several drawbacks. First, they can be broken (although most small
vials are quite robust). Second, if clear bottles are used sunlight can affect the sample
contents, sometimes even changing the concentration of the component of interest. If
samples are always protected from direct sunlight this is not a problem. If protection
cannot be provided, however, brown bottles are preferred.
Other sample containers are made of cloth, paper, and plastic. All three of these can be
quite porous. Cloth is the most porous of the containers and does not make good storage
containers unless drying of the sample is particularly advantageous. Paper bags with or
without plastic or plastic-coated liners are commonly used for soil samples. These bags
are quite handy for many types of samples. Depending on their construction, drying of
the sample may or may not take place.
Of the three common sample container materials, plastic is the least porous to water,
but it can be very porous to organic vapors. In addition, plastics can react to or even be
dissolved by organic compounds. Specialty plastic containers are available. The
specifications of these containers must be investigated before their use, however. As with
glass, clear plastics will allow light to interact with the sample if precautions are not
taken to store them is a dark place. Most plastics can be punctured easily, and so must be
handled carefully. Figure 3.7 shows some common types of sample containers. A
summation of sample containers and their characteristics is given in Table 3.3.

TABLE 3.3 Characteristics of Sample Containers

Material Characteristics Good points Deficiencies

Cloth Strong, unaffected by water Easy to handle

and mark, strong

Contents dry, soil can sift out of
bag

Paper Inexpensive, adversely

affected by water, may react
with contaminants

Easy to handle,
and write on

Soil will dry even in closed bag;
no sifting; writing can smear

Plastic bags Inexpensive, hard to write

on, marking rubs off

Easy to handle,
moisture
retained

Porous to very porous for volatile
organics and gases, subject to
puncture, may react with
contaminant