TNI Logo The NELAC Institute

Standard Interpretation

Standard: 2003 NELAC
Section: (d)
Link to relevant standard


"For corrective action supplemental studies, the assigned values for all analytes requested by the laboratory must not be equal to zero with the exception of the qualitative PCB group and qualitative microbiology."

For years we have been ordering corrective action supplemental studies for PCB's by asking for specific arochlors (that were missed in the original PT sample) and have been allowed to do so. Recently our provider could not fill an order and I went to a different provider. They told me that I could not specify an arochlor for a supplemental study. When I inquired about why I could not do so they told me that I should talk to someone at the LDEQ and they would explain. Before I called them I thought that there must be something in the standard that I was over looking and I found the above citation. I talked to several people at the LDEQ, they were not aware of this citation and they seemed to be easy persuaded either way.

My interpretation of the standard is that we should have never been allowed to specify arochlors for supplemental studies. If this is true then I seem like a big dilemma, because I have not been able to find a single person who already knew about this and I have talked to a lot of people.

We are trying to do the right thing, but we are getting mixed signals and no one seem to be on the same page. There is a specific exception for PCB's, but it is vague and no one is interpreting it the same way. What are we suppose to do?


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

The PCB group is the exception-a laboratory does not need to specify the specific Arochlor and should not specify a specific Arochlor because a component of challenge of the PCB Group is both qualitative and quantitative detection. In other words, the lab must report the correct quantitative value for a specific Arochlor but also be able to report non- detects for the other Arochlors.