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Standard Interpretation

SIR #: 10000
Standard: 2003 NELAC
Section: Appendix D.3.1
Link to relevant standard


In Standard Methods [SM9020] there is a requirement to do at least one positive sample verification monthly, in some cases 10% etc. Question: What if you do not have any positive samples, should you do a positive verification anyway? I see that for DW (source) even if you do not have any positive samples, a positive verification check is to be done quarterly. How about the other type of waters? For example to check any false negatives? Frequency?


(Quality Systems Expert Committee/ NELAP Board, 10-11-09)

Questions involving specific methods should be directed to the writer of the method. For information about the requirements in the NELAC Standard, see D.3.1 b. The requirement for positive controls exists so that the lab can demonstrate that IT isn't the reason there are no positives, i.e., it isn’t doing something that causes no growth.