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Standard Interpretation

Standard: 2003 NELAC
Section: Appendix D.1.6 (a)
Link to relevant standard


Not sure if this is the applicable section for this question. This question has to do with method 524.2 section 11.2.1 which talks about desorb time of about 4 minutes. If DOC and MDL studies show that a 2 minutes desorb time achieves equal or greater method performance as the 4 minute desorb time, will this method modification meet NELAC requirements for drinking water volatile analysis.


(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.

The following is an excerpt of an email regarding the allowable changes to purge time for EPA Method 524.2, Rev. 4.1, received in 11/07 by one State program from EPA Cincinnati:

The statement in the method of "about 4 minutes" was to avoid issues with people demanding that desorb time be exactly 4.00000 minutes. It should be interpreted as times that could be rounded to 4, such as 3.5 to 4.4. It was not meant to permit people to have drastically shorter times.

Modification to methods should be confirmed with the applicable EPA ATP program and Accreditation Program. DOC and MDL studies alone do not necessarily meet the requirements of an allowable method modification. For further consideration please refer to the 40 CFR, Part 141, Expedited Approval of Alternative Test Procedures for the Analysis of Contaminants Under the Safe Drinking Water Act; Analysis and Sampling Procedures, Federal Register / Vol. 73, No. 107 / Tuesday, June 3, 2008 / Rules and Regulations.

During the TNI Laboratory Forum Conference in Miami, scheduled for January 2009, the Assessment Forum (1/13/09) will include topics on What is a Non-Standard Method? When do Standard Methods become non-standard modified methods?