Presampling - Field Sampling: Principles and Practices in Environmental Analysis - page 68

variation on this sampler is a special type in which the soil core is contained in a sleeve or
liner that fits inside the sampler and can be removed with the sample inside. This type of
sampler is particularly good for samples in which contamination or loss of a constituent is
of concern. More sophisticated core samplers remove cores under even more controlled
conditions (e.g., some will even remove a continuous core over the depth of drilling).
Such cores can be important in reducing contamination and maintaining the physical and
chemical integrity of the sample.
All three types of samplers can be power-driven, which allows deeper sampling.
Powered samplers are frequently mounted on vehicles of various types (e.g., on a pickup
truck or a special four-wheel-drive vehicle) and can sample several meters deep. (An
example of this setup is shown in Chapter 5.) For very deep sampling a drill similar to or
the same as the ones used to drill wells may be needed. Deciding on the type of sampler
needed and obtaining the use of the proper sampler is essential in the presampling stage.
Often knowing the depth at which a sample is obtained will be important. For this
situation a core sampler is best. Although this type of sampler will compress the sample it
is still possible to determine the depth from which the sample came. With auger-type
samplers soil from the sides of the hole will invariably be scraped off and included in the
sample. For this reason these types of samplers are not preferred for situations in which
the depth of the sample is important or in which a clear distinction between contaminated
and uncontaminated sample is difficult to determine.
Samplers should be chosen for the type of soil or other material that is to be sampled
and should be easy to use. Many samplers are easy to understand and use, while others
are not, and sampling personnel must be taught how to use them (e.g., well-drilling rigs
will require experienced drill rig crews to operate them). Studies have shown no
difference, however, in analytical results that can be traced back to the type of sampler
used (common soil samplers are shown in Figure 3.6) [6].
3.7.2. Powder and Granular Material Samplers
There is another type of sampler designed for dry powders and granular material. This
instrument looks like a soil core sampler except that it has a solid point on the end and
three compartments along the shaft. There is a sleeve on the outside so that it can be
rotated to cover the compartments. The sleeve is rotated to cover the compartments and
the sampler is inserted into the material to be sampled. Once inserted to the desired depth
the sleeve is rotated so that the powder or granular material can flow into the
compartments. The sleeve is once again rotated to cover the compartments and the
sampler is withdrawn. This type of sampler is most often used to obtain samples in grain
bins.
Using this type of sampler three samples are obtained at the same time, and usually
several additional places in a grain truck or bin are sampled. Only dry powder and
granular material can be sampled effectively using this sampler. Granules larger than a
typical corn seed or moist, fine, wet, and very coarse materials are not effectively
sampled. It could be used to sample coarse, dry sands under the proper conditions,
however. A typical use of this type of sampler would be to obtain corn seed samples to
check for foreign seeds or other contamination and moisture levels.