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Standard Interpretation

Standard: 2003 NELAC
Section: Appendix D.1.1.1 (c)


The composition of a method blank shall consist of a quality system matrix that is similar to the associated samples and known to be free of analytes of interest.
No reference could be found in SW-846 Methods 5035, 8000, and/or 8260 that require a VOA method blank to contain a solid matrix. In fact, in method 5035 section 8.2 it is stated before processing samples to analyze an organic-free water method blank.... Nothing about adding a solid matrix is mentioned.
Adding a solid matrix to a VOA method blank would only potentially add contamination and not be reflective of the cleanliness of the analytical system. Also if one adds a solid matrix (even if it does not contain analytes of interest) to a VOA method blank, should not the same solid matrix be added to all the samples as well?
Basically, is it necessary to add a solid matrix to a VOA method blank when analyzing low level soil samples?
Is it the intent of NELAC's definition of a method blank to override what is presented in the method?
Thank you for your response.


A blank is required to be free of the analytes of interest. Therefore, an appropriate blank for a solid matrix should not contribute contamination.

5.9.3 c) provides the following statements concerning the difference between 5035 and TNI: "The laboratory shall ensure that the essential standards outlined in Technical Modules or mandated methods or regulations (whichever are more stringent) are incorporated into their method manuals. When it is not apparent which is more stringent, the QC in the mandated method or regulations is to be followed."