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Standard Interpretation

Standard: 2003 NELAC
Section: Appendix C.1 (e)
Link to relevant standard


We seem to have a difference of opinion in our lab.
We have a manager that feels that the Table 2 of the EPA Method 548.1 give the criteria to be used for %Recovery for DOCs
They are stating that the Concentration used 100 shows a 95% recovery - they are trying to change their acceptance to 95% +/- 20%
Section 9.3 of the method states to use the R value from this table 2. Aren't these only suggestions of R values? At the moment it is +/- 20% of the mean recovery


(Technical Assistance Committee / NELAP Board, 2/19/09)

Note: Laboratories should attempt to reconcile all differences in the interpretation of the NELAC 2003 standards and/or analytical methods with the applicable EPA Program, Regional Office and/or NELAC accreditation body. The following is an opinion of the current TNI Technical Assistance Committee and NELAP Board.

In reviewing EPA Method 548.1, Revision 1.0, section 9.3 it is our interpretation, which concurred with one of EPA’s Cincinnati’s Chemist, that the laboratory’s mean recovery +/-20% with an RSD of 30% is acceptable for the IDOC, then the laboratory may use the same values or tighter for DOCs in accordance with Chapter V, Appendix C, 1.e.

Table 2 of the method was developed only using 7 replicates, therefore it would be best for a laboratory to adhere to limits for accuracy and precision developed using their own mean recovery.