Water: CWA Methods
Matrix effects that are consistently present in a sample may lead to increased false positive or false negative rates, low or high bias or poorer precision. Additional clean-up steps or other method modifications may mitigate matrix effects.
EPA has provided two tools to help users address their matrix problems:
- A recent regulatory amendment (40 CFR Part 136.6) describes the conditions under which users may modify approve methods without EPA review.
- EPA has updated the 1993 "Pumpkin Book" which describes specific steps users may consider in dealing with matrix effects.
Chapter 4, 5 and 6 of the Pumpkin Book (PDF) (53 pp, 204K) cover "How to Document a Matrix Interference", "Reports of Matrix Interferences," and "Solutions to Matrix Inteferences," respectively. Chapter 8 is titled, "When a Matrix Interference is Demonstrated" and tells what a discharger or laboratory is to do when a matrix interference is encountered.