TNI Logo The NELAC Institute

Combined Interpretations of the 2003, 2009, and 2016 Standards that apply to Volume 1 of the 2016 TNI Standard

Section: Module 4 - 1.5.4

Question:  Since PTs are supposed to be treated like "real environmental samples", 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 previously tested by the laboratory" and therefore 2nd column confirmation is not required?

TNI Response:  The 2003 NELAC Standard (Chapter 5, Appendix D.1.5) and the 2009/2016 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.