Section: V1M4, Section 18.104.22.168.2
40 CFR 136 Appendix B (3) (a) "During any quarter in which samples are being analyzed, prepare and analyze a minimum of two spiked samples on each instrument, in separate batches, using the same spiking concentration used in Section 2." If the variation in the spiking concentration is used to calculate the MDL (MDLS = t(n -1, 1-α = 0.99)Ss), and the lab uses the MDL to calculate a LOQ (maintaining that the LOQ ≥ the lowest calibration concentration), this may not be "a spike at or below the LOQ" as prescribed in TNI V1M4-2016 §22.214.171.124.2 because the concentration value does not play a role in calculating the MDL (DL). It seems the TNI ongoing verification definition differs from 40 CFR. If the lab were to use a concentration at or below the LOQ, this would not always satisfy 40 CFR 136 Appendix B (4) (b) "Include data generated within the last twenty four months, but only data with the same spiking level." The lab seeks clarification on when to verify at or below the LOQ and when to use the same spiking concentration as in the original study. Thank you.
TNI FINAL RESPONSE:
The TNI requirement does differ from the EPA MDL procedure in that it requires that the spikes used for the ongoing verification of the MDL be "at or below the LOQ." The EPA MDL procedure has no limitations for the spike concentration used in the initial determination and ongoing verification, other than they be at the same concentration. In order to comply, the LOQ would therefore be set at the concentration at or above the lowest calibration standard or the concentration of the spiked samples used to determine the MDL, whichever is greater. This will ensure that the spike concentration is at or below the LOQ and that the ongoing verification can be carried out using spikes of the same concentration as the initial determination, as is required by the TNI standard. Performing the EPA MDL procedure alone is not adequate to meet the requirements set forth in the TNI MDL standard. However, if you are required by the method to use the 40 CFR 136(b), then the EPA method must be used, per the first sentence of V1M4 §126.96.36.199.