Section: V1M6, Section 188.8.131.52 (b)
Section 184.108.40.206b in TNI Standard V1M6 is not clear in regard to whether samples with levels of activity (below three (3) times the MDA) are appropriate for use as MD as a measure of precision when the target analyte is not present.
According to Section 220.127.116.11b(i), "Duplicate analyses provide a measure of precision when the target analyte is present in the sample chosen for duplication." 18.104.22.168b(iv) states that "When samples have low levels of activity (less than approximately three (3) times the MDA) the laboratory, at its discretion, may analyze MS/MSD to determine reproducibility within a Preparation Batch in place of a MD."
The matrix of our Isotopic Gamma samples is NPW. We currently perform one MD per batch comparing activities for Ru-106, Cs-137 and Zn-65. Ru-106, Cs-137 and Zn-65 are typically undetected in our routine environmental samples. We don’t know whether Ru-106, Cs-137 and Zn-65 are absent or present at a low level.
1. Is it acceptable to use the MD as a measure of precision when the analyte is not known to be present?
TNI FINAL RESPONSE:
Yes, it is acceptable to use the MD as a measure of precision when the analyte is not known to be present, as long as acceptance criteria has been established and documented by the laboratory.