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

Section: 1.7.2

Question:  With regards to the requirement of spiking all targeted components over a 2-year period, is this an overall requirement per ANALYTE or per METHOD?  As an example, we analyze pesticides by EPA 525.2 and EPA 8270C.  Can we spike all target analytes for one method and cover the other?  Or must we spike all for both methods?

TNI Response:  The standard for multi-analytes tests requires that all targeted components be included in a spike mixture for evaluation during a 2-year period and includes any reported analyte (whether detected or not).The committee noted that the preparation for 525.2 and 8270C are different, and spike results could differ. Therefore, each method requires a separate spiking schedule. Methods 624 and 8260, which use the same preparation procedure, could use the same spiking study.


Question:  Under Matrix Duplicates it states that the precision may be expressed as RPD or another statistical treatment. We do not do matrix duplicates, we perform sample duplicates only and use percent recovery. Are we required to run matrix duplicates, or are we okay running sample duplicates only? If we are allowed to run sample duplicates only, do we have to express precision as RPD, or can we stick to percent recovery? If we need to switch to matrix duplicates do we need to use RPD or can we use percent recovery?

TNI Response:  Any laboratory-duplicated sample (however named, such as matrix duplicates, sample duplicates, or matrix spike duplicates) must be evaluated for precision. A percent recovery evaluates accuracy, but not precision. Precision must be evaluated by a statistical technique such as RPD, absolute difference or Percent relative standard deviation (% RSD).