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Procedures for Detection and Quantitation
Federal Advisory Committee on Detection and Quantitation for Uses in Clean Water Act Programs
Meeting #10
Matrix Effects
Definition:
Matrix Effects: Matrix effects are effects associated with a unique matrix which adversely impact the performance of an analytical process. The impacts may include increased false positive or false negative rates, low or high bias or poorer precision.
Draft Recommendations:
(note: Recommendations are in bold font. Explanatory discussion is in normal font.)
The FACDQ recommends that EPA publish new guidance on matrix effects. At a minimum, the guidance should outline the appropriate level of matrix effects validation necessary for method promulgation for analytical methods to be considered for 40 CFR Part 136. The FACDQ recommends that EPA adhere to this guidance in methods it develops and validates for promulgation in 40 CFR Part 136. This guidance should also address the following:
- Determining the appropriate number of matrices to take into account.
- The level of validation required verses the proposed scope of use for the analytical method.
- Matrix effects validation in the ATP program.
- Impacts for consensus standards methods considered for part 136.
Such guidance could be used by EPA during method validation to evaluate the ruggedness of the performance of an analytical method on different types of sample matrices. Furthermore, interested stakeholders could also implement the guidance and submit the data for consideration during rulemaking thus expanding the understanding of the methods performance while minimizing the cost to EPA.
The FACDQ recommends that EPA develop a consistent protocol on how to demonstrate matrix effects. The FACDQ believes such a protocol should be sensitive to cost and required level of effort to ensure that it is applied consistently.
Questions to be addressed by the protocol:
- What level of effort is necessary to determine if the matrix effects can be resolved by modifications of the analytical method that are within the flexibility allowed within the method?
- What set of experiments and data interpretation framework would suffice to demonstrate a matrix effect if performed properly?
- Who should be responsible for implementing a procedure to determine a matrix specific QL?
- How broadly applicable shall a matrix effect be considered? What level of demonstration should be considered adequate for a single facility? What level of demonstration should be undertaken to extend the matrix specific QL to other like wastewaters?
The protocol could also be used by permitees petitioning for consideration of matrix effects during the permitting process. Having one set of guidance applied across the nation would facilitate comparability and consistency and could result in cost savings and efficiency. This procedure could also be applied by stakeholders to proposed Part 136 methods to provide information on the performance of the method to be considered during promulgation.
The FACDQ recommends that EPA develop a procedure for determining matrix-specific detection or quantitation limits for use where appropriate. Again, such a protocol should be sensitive to cost and required level of effort.
Questions that should be addressed include:
- Who should be responsible for implementing a procedure to determine a matrix specific QL?
- How broadly applicable shall a matrix effect be considered?
- What level of demonstration should be considered adequate for a single facility?
- What level of demonstration should be undertaken to extend the matrix specific QL to other like wastewaters?
Once a matrix effect has been established, EPA should provide a well-defined protocol for developing a matrix specific detection or quantitation limit. Such a protocol would make clear what actions are needed and would facilitate comparability and consistency and could result in cost savings and efficiency.
When considering future updates of QLnat, the FACDQ recommends that EPA take into consideration any experience with the performance in different matrices when considering a revision of the QLnat.
EPA should establish the level of concern that triggers the need to take these effects into account. For example, should problems with matrix effects in one industry dictate a new, and likely higher quantitation level for all other matrices.
Because of the nature of the future update process recommended by the FACDQ, there will be considerably more experience on how well the method performs on real world samples than was available during the new method promulgation process. This experience, and the insights into method performance (or limitations) it provides, should be taken into account when considering updating or revising a QLnat.