Air Sampling for Industrial Hygiene is one of a few analytical methodologies where blank use is not only recommended but often prescribed. Many consultants do not see why they need to pay for analysis of the blank samples if the results often come “non-detected”.
There are three reasons why.
Legal: To comply with the law, you need to follow the standard method. If the method says to use 2 blanks, you must use 2 blanks. If you followed the method, then nobody can question your sampling procedure.
Quality of the Results. Sometimes the sample gets contaminated after sampling is complete, often during shipping or storage. Let’s say you collected a sample of formaldehyde and shipped them to my lab in London, Ontario, Canada. We tested them and reported you results of 0.2 ug/sample. Then we tested a field blank sample (that you send us) and found that it also has 0.2 ug of formaldehyde per sample. So the true amount of formaldehyde collected at the client’s location is 0.2-0.2=0 (not detectable), and all formaldehyde that we detected is background contamination absorbed on the sampling media during shipping or storage.
Analytical Requirements. Some tests cannot be performed without the blanks, because the lab result will be biased. Those are the tests where the client expects extreme sensitivity comparable with the method sensitivity.
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