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Standard Interpretation

Standard: 2009 TNI
Section: V1M4, Section 1.5.4


Since PTs are supposed to be treated like "real environmental samples",<sup>1</sup> must laboratories perform second column confirmation for "hits" in PT samples analyzed by GC methods? Or, would a PT sample be considered "a positive result detected on a sample from a location that has been <sup>3</sup> and therefore 2nd column confirmation is not required?


(Quality Systems Expert Committee and NELAP AC, 2-24-14)

The 2003 NELAC Standard (Chapter 5, Appendix D.1.5) and the 2009 TNI Standard (V1M4 1.5.4) require the laboratory to perform confirmations according to the method. The approved methods in Standard Methods for the Examination of Water and Wastewater and the applicable U.S. EPA methods require confirmation on "unfamiliar samples." A PT sample (by design, a sample with unknown composition) is a sample that is "unfamiliar" to the laboratory and therefore requires confirmation per method requirements.