Standard: 2003 NELAC
Section: Appendix.C.3.1 and C.3.2
The Standard states you must use the "established test method acceptance criteria" or "client data quality objectives for accuracy" when confirming the LOQ. First of all, our clients virtually never set 'data quality objectives for accuracy', they rely on the lab to set that for the methods. Second, only new methods set acceptance criteria at the LOQ. What criteria should be used, for instance, for EPA 8000-series tests, which only designate an 85-115% CCV criteria at mid-level for most methods, but usually mandate no specific criteria for LCSs? While using our lab-generated LCS criteria may work, those numbers are usually developed using mid-level spiking levels.
Many new methods state CCVs must be within 60-140% at the LOQ, while LCSs may be within 50-150% of expected values. Mid-level criteria are usually tighter.
Last, there's a problem with respect to the statement in TNI Standard (section 188.8.131.52), "The annual LOQ verification is not required if the LOD was determined or verified annually on that instrument." I have seen several LOD/MDL studies that have good precision (produces a relatively low LOD), but the accuracy is terrible (average of 250% recovery). In my opinion, being able to physically see something at extreme low levels doesn't mean you can accurately determine the concentrations at low-levels. Some range should be set like 50-150% at the LOQ for confirmation.
TNI FINAL RESPONSE:
(Quality System Expert Committee/NELAP Accreditation Council, 9-20-14)
It is up to the laboratory to determine these criteria if they are not specified in the method or by other rule or regulation. Webcast training on LOD and LOQ is now available on the TNI website under the Educational Delivery System tab.