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Standard Interpretation

Standard: 2003 NELAC
Section: 2


We are currently accredited for method SW 846 8151, but we want to add Pentachlorophenol by 8151 to our scope. Pentachlorophenol is not listed as requiring PT with the other Herbicides that are analyzed by 8151 that are listed. Therefore, I interpret that as Pentachlorophenol by method 8151 does not require PT.

Our Accrediting Body says otherwise. They contend that because Pentachlorophenol is listed under the Acid Extractables (Method 625 or 8270) that require PT, it also requires PT if we want to add it to our 8151 scope.

Please advise. Thank you.


The ABs are correct in requesting the analysis of PTs where available by analyte/matrix. While the 2003 NELAC Standard defined an FoPT as having all three elements of matrix, method/technology, and analyte/analyte groups, PT data was not available to establish separate FoPTs according to method/technology. The 2003 Standard also specified that sufficient PT data had to be available, specified as at least 10 valid PT studies with at least 20 participant laboratories in each study, in order to establish concentration ranges and acceptance limits for FoPTs.

When this SIR was initially submitted for consideration, the TNI PT Program worked to establish additional FoPTs for so-called "dual-purpose" and "overlapping" analytes. The SCM FoPT Table that went into effect on 1/3/2012 added an additional listing for Pentachlorophenol in the grouping with other Herbicides analytes for possible use with methods such as EPA 8151. At that time, insufficient PT data was available to support the addition of Pentachlorophenol to the NPW FoPT Table.

The TNI PT Program has no control over the business practices of PT Providers on how they package, market, and distribute their PT samples. Therefore, the only recourse within the auspices of TNI are to petition the PTPEC to add the analyte in question as a separate entry with separate concentration range and acceptance limits. This could be done by submitting an Analyte Request Application to the PTPEC, with a TNI NELAP AB sponsor and supporting PT data justifying the addition of the requested analyte.