Standard Interpretation

Standard: 2003 NELAC
Section: 5.5.4.4; 5.5.4.5; Appendix C3.3 (b)
Link to relevant standard

REQUEST:

This has been passed around previously, but wasn't officially put out for interpretation, and would be good for open discussion/the forum.

non-standard methods/modification of methods

2 questions concerning mercury:

1) EPA 245.1 vs SW846 7470: SWrequires heating the standards, the EPA method doesn't. Is it acceptable to do the same for both (i.e., batch them together), and still be accredited for both methods in non-potable water? The Standard says validation is to be as extensive as necessary and C3.3b) only applies if the method was not in use prior to 7/03. If there are 20 years of at least 4 PT standards per year without a failure, the method should be sufficiently validated. This can't be left to individual state interpretation since one lab could be required to do two digestions/calibrations and other labs not, depending on where they're located. What if a lab is bidding on work in a state that allows the modification, but the home state doesn't? The real question is: Who decides if the modification is acceptable, if it has been sufficiently validated, and whether a lab can be accredited for "the method"? (especially when something is common practice)

2) Same issue with using HCL instead of H2SO4 to make the stannous chloride solution (the instrument manufacturer recommends HCl although the method says H2SO4).

TNI FINAL RESPONSE:

(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 response was obtained by the TNI Technical Assistance Committee TAC from EHSG MICE.

First off, we would like to clarify a common misnomer pertaining to SW-846 methods that is alluded to in question one. Please stress to this member that Methods 245.1 and 7470 are in fact both EPA publications. The former from the Office of Water while the latter is published by the Office of Solid Waste.

Now to answer the questions, it is recognized that historically the most common practice was to digest the calibration standards in the same manner as the samples. However, with the newer instrumentation direct calibration using an aqueous standard is now possible, so the digestion steps are no longer necessary. So, in this particular case it depends more on the instrumentation and the manufacturer's calibration requirements rather than what is specified in the method. In addition, using EPA OSW's PBMS approach any calibration format is considered acceptable as long as adequate performance data are generated. If the desired sensitivity is attainable and QC data meet the project requirements, the practice of not digesting standards should be considered acceptable. The direct calibration option we alluded to will be included in the revised mercury Methods 7470A and 7471B that are due to be published with the SW-846 Fourth Edition update, hopefully late next year.

Using this same logic, if the instrument manufacturer recommends HCl to prepare the stannous chloride solution this again would be a perfectly acceptable modification under the OSW's PBMS policy. After all the instrument manufacturer should know best what operating conditions for their equipment will generate the most reliable data.

The following response was obtained by the TNI Technical Assistance Committee TAC from EPA OSTCWA Methods.

1) SW requires heating the standards, while the EPA method doesn't. Is it acceptable to do the same for both (i.e., batch them together)? Either digesting all of the standards and QC samples for 245.1 along with 7470, or not digesting the standards and analytical QC (preparation QC like MB, LCS, MS, etc. would still be required) If there are 20 years of at least 4 PT standards per year without a failure, doesn't that show that the modification is sufficiently validated? We know of regulatory authorities that do not view this modification consistently.

* For CWA compliance monitoring - we agree that the modification has been sufficiently validated, provided validation (including QC) requirements in the method and in 40 CFR 136.6 have been met.

2) Same issue with using HCL instead of H2SO4 to make the stannous chloride solution (the instrument manufacturer recommends HCl although the method says H2SO4). In this particular case can either acid be used regardless of what the method states? Is there any indication that the change in acid would compromise the recovery of the mercury?

*Same answer for CWA; i.e., if QC requirements in the method and in part 136.6 have been met.

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These modifications were made long before 136.6 appeared in the CFR and, therefore, the modifications should be allowed because of their history of use. If the labs have been doing the QCS, MS, MDL, LRB, LCS, and recovery tests required by Section 9 of 245.1, and other QC tests required by the method, and have met the QC acceptance criteria, they've already met the requirements of 136.6. In that case, the modifications should be allowed and grandfathered.