An Overview of Basic Principles of Analytical Methods - Field Sampling: Principles and Practices in Environmental Analysis - page 253

One of the most important factors to be considered and maintained in the field
sampling process is cleanliness. This factor, along with sample integrity and
documentation, is critical to the valid and accurate sampling process. All the sampling
equipment used must be thoroughly cleaned (and sterilized if necessary) and stored in
such a way as to ensure cleanliness upon initial use in the field. Also, all equipment must
be thoroughly cleaned and rinsed between each sampling event if the equipment is reused
in the field. It is imperative that sample integrity be maintained both in terms of
cleanliness and correctness in composition from site to site. It is very easy to contaminate
a whole sampling event with one poor equipment cleaning or by failure to change gloves
between sampling a badly contaminated field, a field with low levels of contaminant, or a
field that is clean.
Maintaining sample integrity requires that care be taken at all steps of the sampling
event to ensure a representative sample is obtained and sent to the laboratory to be
analyzed. For water or liquid samples, this may simply require checking for immiscible
layers or fractions in the liquid sample. For soil it may require subsampling from various
places and thoroughly mixing the subsamples before the final analytical sample is taken.
Unless great care