The use of blanks is an important quality control measure when collecting water samples in the field. Field, laboratory and trip blanks are used to determine the integrity of collected samples.
A field blank is a container of water, quality assured to be free of any of the substances – organic, inorganic or both – that are to be tested for in the real samples. The container is taken into the field and exposed to the atmosphere of the site for a period of time.
A trip blank is a container of laboratory reagent water that is shipped, unopened, to and from the field, with empty and full sample containers. Its purpose is to identify contaminants introduced into samples during transit to and from the laboratory.
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There is still the possibility that contamination can be introduced in the laboratory, so the trip blank is compared with a laboratory blank. Contaminants found in the trip blank, but not in the laboratory, blank may indicate a problem with transportation, storage or container preparation among others.